CA2065405A1 - Measuring device and process for determining the level in fluid containers, preferably for tank installations, and use of a sound waveguide - Google Patents
Measuring device and process for determining the level in fluid containers, preferably for tank installations, and use of a sound waveguideInfo
- Publication number
- CA2065405A1 CA2065405A1 CA 2065405 CA2065405A CA2065405A1 CA 2065405 A1 CA2065405 A1 CA 2065405A1 CA 2065405 CA2065405 CA 2065405 CA 2065405 A CA2065405 A CA 2065405A CA 2065405 A1 CA2065405 A1 CA 2065405A1
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- Prior art keywords
- sound
- fill level
- temperature
- fluid
- fluid volume
- Prior art date
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- 238000002604 ultrasonography Methods 0.000 claims abstract description 34
- 238000012937 correction Methods 0.000 claims abstract description 14
- 238000009826 distribution Methods 0.000 claims abstract description 12
- 238000012935 Averaging Methods 0.000 claims description 11
- 238000012360 testing method Methods 0.000 claims description 6
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- 230000001419 dependent effect Effects 0.000 abstract description 2
- 230000000875 corresponding effect Effects 0.000 description 8
- 238000011156 evaluation Methods 0.000 description 8
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- 238000009529 body temperature measurement Methods 0.000 description 3
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- ZMJBYMUCKBYSCP-UHFFFAOYSA-N Hydroxycitric acid Chemical compound OC(=O)C(O)C(O)(C(O)=O)CC(O)=O ZMJBYMUCKBYSCP-UHFFFAOYSA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 230000002301 combined effect Effects 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
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- 239000007788 liquid Substances 0.000 description 1
- 239000002480 mineral oil Substances 0.000 description 1
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- 239000010959 steel Substances 0.000 description 1
- 235000012222 talc Nutrition 0.000 description 1
- 230000001702 transmitter Effects 0.000 description 1
Landscapes
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
Abstract
Abstract In a level measuring device for containers (20) filled with fluid (10), preferably tanks in tank installations, the fill level height h is determined from the transit time of ultrasound pulses which are emitted by first sound pulse transmitters (S1) along a main measuring path (8) extending from the bottom region of the tank (20) to the fluid surface (9, 9') and reflected from the fluid surface (9, 9') to first sound pulse receivers (S1). Means are provided in the form of temperature sensors (1, 15, 16) for finding the temperature distribution throughout the fill level height h.
Processing the measurements provides a mean temperature TM
in the fluid volume. In addition to the main measuring path (8) there is a reference path (11) in the fluid volume, with second sound pulse transmitters and receivers (S2) and a reference temperature sensor (14) to measure a reference temperature TRef. The reference path makes it possible to find the sound velocity v*(TRef) in the fluid volume at the reference temperature TRef from the measured difference in transit time, so that a temperature-corrected sound velocity v(T) in the fluid volume: v(T) = v*(TRef)[1+Kk?.DELTA.T), and thus a temperature-corrected fill level height h(T) = v(T)?tH, are found, in which .DELTA.T = TM-TRef , and Kk is a medium dependent correction factor. The subject of the invention also includes a process for determining the fill level and an advantageous use of a measuring tube (24) comprising a first and a second sound waveguide (4,5).
Processing the measurements provides a mean temperature TM
in the fluid volume. In addition to the main measuring path (8) there is a reference path (11) in the fluid volume, with second sound pulse transmitters and receivers (S2) and a reference temperature sensor (14) to measure a reference temperature TRef. The reference path makes it possible to find the sound velocity v*(TRef) in the fluid volume at the reference temperature TRef from the measured difference in transit time, so that a temperature-corrected sound velocity v(T) in the fluid volume: v(T) = v*(TRef)[1+Kk?.DELTA.T), and thus a temperature-corrected fill level height h(T) = v(T)?tH, are found, in which .DELTA.T = TM-TRef , and Kk is a medium dependent correction factor. The subject of the invention also includes a process for determining the fill level and an advantageous use of a measuring tube (24) comprising a first and a second sound waveguide (4,5).
Description
MEASURING DEVICE AND PROCESS FOR DETERMINING THE
FILL LEVEL IN FLUID CONTAINERS, PREFERABLY FOR
TANK INSTALLATIONS, AND USE OF A SOUND WAVEGUIDE
The invention relates to a fill level measuring device for containers that are filled with fluid, preferably for tanks of tank installations, where the fill level height is determined from the sound transit time of ultrasound pulses, which are emitted along a main measuring path extending from the bottom region of the container up to the surface of the fluid by first sound pulse transmitters and are reflected from the surface of the fluid to first sound pulse receiv-ers.
A fill level measuring device of this kind is known from European Patent Document A3 0 106 677. It operates by the principle of echo depth sounding systems. Path lengths are derived from the transit time of sound pulses. This transit time or transit time difference is obtained in each case from the measured time difference elapsing between the transmission of an ultrasound pulse until the reception of the ultrasound pulse reflected by the surface of the fluid.
The sound pulse transmitters and sound pulsQ receivers are preferably embodied as transmit-receive test heads, which are suitable for both transmitting and receiving ultrasound pulses. The sound velocity in a fluid volume is dependent :
:
s on the density. To obtain an average, density-corrected sound velocity in the fluid volume, reference reflectors distributed over th~ fill level height at a defined spacing from one another and from the sound pulse transmitters and receivers are provided in the known fill level measuring device. The ultrasound pulses reflected at the reference reflectors produce transit time differences, which together with the associated known sound travel distances are used to ascertain an average sound velocity that takes the density in the fluid volume into account. Additionally, a tempera-ture sensor is disposed in the lower region of the contain-er, and with it, the temperature of the fluid at some point can be ascertained. The calculation of an average tempera-ture of thP fluid volume is also provided. The average temperature is needed in order to be capable of calculating the density and thus the container contents once the fill level height is ascertained. To calculate the average temperature, known linear characteristic curves ~ v/ T are the point of departure; they indicate the variation in the sound velocity as a function of the variation in tempera-ture. This known quotient can be macle equivalent to a quotient ascertained by measurement, in which the difference VL VRef is located in the numerator and the difference, TAV - TRef, is located in the d2nominatsr; vL stands for an average sound velocity, VRef stands for a reference sound ; ., .
. . .
,, : ~ - :
, ~ .
, , ~
velocity, TAV stands for the average temperature, and TRef stands for a reference temperature. The expense and compli-cation in terms of apparatus and electronics relative to the accuracy is relatively high in this known fill level measur-ing device. Moreover, a number of control measurements must be carried out, because as a result of the relatively high number of reference reflectors that are distributed over the fill level height, scattered beams occur which have to be eliminated in the measurements.
The object of the invention is to create a fill level measuring device of the above generic type that makes do without reference reflectors and thus avoids scattered beams, and with which nevertheless high accuracy and reli-able operation can be attained. An accuracy of at most + 1 mm measuring tolerance, but preferably even less, in the fill level indication should be attained. The expenditure for measurement pickups and the associated expenditure for electronic processing of measured values should be kept within limits.
To attain this object, the fill level measuring device of the type defined at the outset above is characterized in accordance with the invention in that ', :. . , ! :
': ~
- in the fluid volume, in addition to the main measuring path, a reference path is provided, including at least one second sound pulse transmitter and one second sound pulse receiver at the beginning and end of the reference path, respectively, wherein at least one reference temperature sensor is provided for measuring a reference temperature TRef f the partial fluid volume of the reference path, and by means of the reference path, the sound velocity v ~TRef) in the fluid volume at the reference temperature TRef can be ascertained on the basis of a given measured transit time difference At - so that a temperature-corrected sound velocity v(T) in the fluid volume:
v (T) = V (TRef ) [ 1 + Kk ~T
and thus a temperature-corrected fill level height h (T) = V (T) tH
result, in which ~T = TM - T
Kk = 1 v(Tl) - v(To) ~T ( 0 ) T T1 To and Tl, To are two different temperatures of the fluid, measured on the reference path with a reference temperature sensor and v(T1), v(To) are the associated sound velocities measured with the reference path, and Kk is a correction - - : .:
, ~
, ::
::
FILL LEVEL IN FLUID CONTAINERS, PREFERABLY FOR
TANK INSTALLATIONS, AND USE OF A SOUND WAVEGUIDE
The invention relates to a fill level measuring device for containers that are filled with fluid, preferably for tanks of tank installations, where the fill level height is determined from the sound transit time of ultrasound pulses, which are emitted along a main measuring path extending from the bottom region of the container up to the surface of the fluid by first sound pulse transmitters and are reflected from the surface of the fluid to first sound pulse receiv-ers.
A fill level measuring device of this kind is known from European Patent Document A3 0 106 677. It operates by the principle of echo depth sounding systems. Path lengths are derived from the transit time of sound pulses. This transit time or transit time difference is obtained in each case from the measured time difference elapsing between the transmission of an ultrasound pulse until the reception of the ultrasound pulse reflected by the surface of the fluid.
The sound pulse transmitters and sound pulsQ receivers are preferably embodied as transmit-receive test heads, which are suitable for both transmitting and receiving ultrasound pulses. The sound velocity in a fluid volume is dependent :
:
s on the density. To obtain an average, density-corrected sound velocity in the fluid volume, reference reflectors distributed over th~ fill level height at a defined spacing from one another and from the sound pulse transmitters and receivers are provided in the known fill level measuring device. The ultrasound pulses reflected at the reference reflectors produce transit time differences, which together with the associated known sound travel distances are used to ascertain an average sound velocity that takes the density in the fluid volume into account. Additionally, a tempera-ture sensor is disposed in the lower region of the contain-er, and with it, the temperature of the fluid at some point can be ascertained. The calculation of an average tempera-ture of thP fluid volume is also provided. The average temperature is needed in order to be capable of calculating the density and thus the container contents once the fill level height is ascertained. To calculate the average temperature, known linear characteristic curves ~ v/ T are the point of departure; they indicate the variation in the sound velocity as a function of the variation in tempera-ture. This known quotient can be macle equivalent to a quotient ascertained by measurement, in which the difference VL VRef is located in the numerator and the difference, TAV - TRef, is located in the d2nominatsr; vL stands for an average sound velocity, VRef stands for a reference sound ; ., .
. . .
,, : ~ - :
, ~ .
, , ~
velocity, TAV stands for the average temperature, and TRef stands for a reference temperature. The expense and compli-cation in terms of apparatus and electronics relative to the accuracy is relatively high in this known fill level measur-ing device. Moreover, a number of control measurements must be carried out, because as a result of the relatively high number of reference reflectors that are distributed over the fill level height, scattered beams occur which have to be eliminated in the measurements.
The object of the invention is to create a fill level measuring device of the above generic type that makes do without reference reflectors and thus avoids scattered beams, and with which nevertheless high accuracy and reli-able operation can be attained. An accuracy of at most + 1 mm measuring tolerance, but preferably even less, in the fill level indication should be attained. The expenditure for measurement pickups and the associated expenditure for electronic processing of measured values should be kept within limits.
To attain this object, the fill level measuring device of the type defined at the outset above is characterized in accordance with the invention in that ', :. . , ! :
': ~
- in the fluid volume, in addition to the main measuring path, a reference path is provided, including at least one second sound pulse transmitter and one second sound pulse receiver at the beginning and end of the reference path, respectively, wherein at least one reference temperature sensor is provided for measuring a reference temperature TRef f the partial fluid volume of the reference path, and by means of the reference path, the sound velocity v ~TRef) in the fluid volume at the reference temperature TRef can be ascertained on the basis of a given measured transit time difference At - so that a temperature-corrected sound velocity v(T) in the fluid volume:
v (T) = V (TRef ) [ 1 + Kk ~T
and thus a temperature-corrected fill level height h (T) = V (T) tH
result, in which ~T = TM - T
Kk = 1 v(Tl) - v(To) ~T ( 0 ) T T1 To and Tl, To are two different temperatures of the fluid, measured on the reference path with a reference temperature sensor and v(T1), v(To) are the associated sound velocities measured with the reference path, and Kk is a correction - - : .:
, ~
, ::
::
2~
factor that on the basis of the measurements of T1, To~
v(Tl~ ~ v(To) indicates the standardized variation in the sound velocity per deyree of temperature variation of the fluid volume, and wherein further tH is the portion of the transit time difference ~t1 corresponding to the fill level height, which difference is measured with each of the first sound pulse transmitters and receivers (S1).
Advantageous features of the fill level measuring device are disclosed in claims 2-15.
The advantages attainable with the invention are above all that no reference reflectors are disposed in the way of the main measuring path; consequently the ultrasound signal transmitted to the surface of the fluid and sent back by it reaches the sound pulse receiver practically unhindered.
The means for temperature distribution over the fill level ~-height need not be located in the cone formed by the beams of the main measuring path, but can instead be located laterally thereof.
The means for detecting the temperature distribution, according to claim 2, preferably includes temperature sensors, which are disposed in a plurality of measuring points distributed over the fill level height, and from the :, , ., ~ , . . .
' ~r~ s temperature measurement values of which the mean temperature TM of the fluid volume can be derived by averaging. It was already possible to attain very good measuring results with a fill level measuring device according to claim 3, in which the means for detecting the temperature distribution include at least one temperature sensor, disposed in the vicinity of the bottom, and at approximately one-third and approximately two-thirds of the maximum fill level of the container.
The temperature sensors are preferably secured to the outer circumference of a sound waveguide, which is described in detail in claims 4-11. For the main measuring path, accord-ing to claim 4, a vertically aligned sound waveguide is provided that extends from the bottom region of the contain-er up to a height that is located above the maximum fill level. The interior of this first sound waveguide communi-cates via openings with the remaining fluid volume. On its lower end, there is a sound pulse transmitter for transmit-ting an ultrasound beam in the direction of the surface of the fluid volume, and a first sound pulse receiver for receiving the ultrasound beam reflected from the surface.
The temperature sensor~ are preferably secur~d to the outside of this first sound wavPguide, as mentioned.
According to claim 6, the reference path is assigned its own second sound waveguide, to which the ~ound pulse transmitter .: ~
- ' '```' and receiver and the at least one reference temperature sensor are secured, and the interior of which communicates with the remaining fluid volume via at least one opening.
It is favorable if the second sound waveguide for the reference path is embodied as a transverse tube disposed near the bottom of the container (claim 7). A compact measurement array that is easy to mount is attained by means of a combined sound waveguide in accordance with claim 8, in which the first sound waveguide for the main measuring path is structurally united on its lower end with the transverse tube for the reference path, to make a T-shaped, continuous-ly hollow measurement tube.
Other advantageous features of the combined sound waveguide, in particular relating to the disposition of the first sound pulse transmitter and receiver and further, third sound pulse transmitters and receivers, for ascertaining the sump level, are disclosed in claims 9-11.
An advantageous fastening of the first sound waveguide or of the combined sound waveguide to a fill tube passed through the container dome lid, and the laying of the measuring and current supply lines and their ducting through the dome lid are recited in claim 12.
.
~ ~ , Piezoceramic sensors are preferably used as the sound pulse transmitters and receivers for the fill level measuring device; suitably, their sound transit times are each mea-sured from the moment the sensor short circuits until the first amplitude of an echo arrives (claim 13). Good mea-surement accuracy with measured value tolerances of less than 1 mm are obtained if counting pulses specified in a fixed rhythm are used to detect the sound transit times of a transit time counter oscillator, and if the frequency of the transmitted ultrasound pulses are in a ratio of 1:3 to 1:6 with the frequency of the transit time counter oscillator (claim 14). According to claim 15, it is especially favor-able if the frequency of the transmitted ultrasound pulses is 2 MHz and that of the transit time counter oscillator is 8 MHz.
The subject of the invention is also a method for determin-ing the fill level in containers filied with fluid, pre~era-bly in tanks of tank installations, with determination of the fill level from the sound transit time of ultrasound pulses, which are emitted along a main measuring path, extendlng from the bottom region of the container to the surface of the fluid, by first sound pulse transmitters and are reflected from the surface of the fluid to first sound pulse receivers.
, ~
:, , ,' ;:,,' . '~. :
'~
This generic method, which is likewise known from the European Patent Document A3 0 106 677 mentioned at the outset, is intended to be embodied, analogously to the fill level measuring device according to the invention, in which a wa~ that it is unnecessary to work with a multiplicity of reference measuring beams that are transmitted by a sound pulse transmitter and after being reflected from the refer-ence reflectors are received by a sound pulse receivers and carried further for further processing. Instead, the method according to the invention should enable ascertaining the fill level at least equally accurately, if not even more accurately, in proportion to the electrical, mechanical and electronic expenditure, without using reference reflectors.
To attain this object, the method according to the invention is characterized in that a temperature-corrected sound velocity vtT) in the fluid volume is ascertained in accor-dance with the following equation:
v(T) = v (TRef) [1 + Kk ]
and from that a temperature-corrected fill level h(T) = v(T) tH
is ascertained, in which the correction factor Kk is defined by the following equation:
Kk = 1 v(Tl) - v(To) ~TV (T o ) , ,. ,~ , . - . - :
, : . . . ` ` ~:: `
:~ ` , ': , ;
2~ s wherein ~T = Tl - To ~ T = T - T
and in which the following symbols have the following meanings:
TM, the mean temperature of the fluid volume derived by measuring the temperature at a plurality of measurement points distributed over the fill level height;
v , the sound velocity, ascertained at the reference temper-ature TRef along a reference path of known length located in the fluid volume, this velocity being derived from the transit time differences of the ultrasound pulses that ensue between a second sound pulse transmitter and a second sound pulse receiver at the beginning and end of the reference path, respectively;
TRef, the reference temperature at the reference path at the time of the particular transit time measurement;
T1, To~ the different temperatures of the fluid, measured at the reference path;
v(Tl) ~ v(To) ~ the associated sound velocities ascertained with the reference path;
Kk, a medium-specific correction factor, which indicates the standardized variation in the sound velocity per degree of temperature variation of the fluid volume; and tH~ the portion of the transit time difference ~t 1 ~ corre-sponding to the fill level, that is measured with the first sound pulse transmitters and receivers (S1), respectively.
Advantageous further features of this method are disclosed in claims 17-21.
The advantages attainable with this method are considered above all to be that for every fill level measurement, a current correction factor is determined, even whenever there is no linear relationship between the variation in sound velocity as a function of the temperature variation of the fluid volume. This advantage also applies to the fill level measuring device of the invention. The mean temperature TM
can be determined very accurately, as will be explained in further detail hereinafter, by measuring the temperature at a plurality of measuring points distributed over the fill level height.
- , . . . . . ~
.
! ;, i. .
z~
For the practical application of the method, it is es~ecial-ly advantageous if according to claim 16, in the ascertain-ment Gf the fill level height h(T), the sump height b in the container is also taken into account, and that the fill level height h (T) taking the sump height into account is ascertained in accordance with the following equation:
h (T) = tH v(T) + ts v(T) - a + b, wherein the following symbols have the following meanings:
tS, the portion of the transit time difference ~t S corre-sponding to the sump height, which is measured with a third sound pulse transmitter and receiver (S3), which is disposed in the region near the bottom of the fluid volume;
a, the distance, measured vertically between the flrst and third sound pulse transmitters and receivers (S1-S3), and b, the sump height measured by the third sound pulse trans-mitters and receivers (S3).
It is favorable to amplify the sound pulses, received by the sound pulse receivers, as a function of the sound transit time, in order to keep relatively constant for both short and longer transit times of the first amplitude.
. ; . , : ; .
.
.
x~
In combinatio~ with the main measuring path extending inside a sound waveguide, it is especially advantageous that feedback from surface motion of the fluid upon the fill level is minimized by the sound waveguide itself and by multiple measurements. Since the first second sound waveguides, or the measuring tube formed by the combination of the two, communicates with the fluid volume via openings, provision is made on the one hand for a temperature balance within the main measuring path and the reference measuring path and the remaining fluid volume; on the other hand, this avoids so-called sound drifts, because the main and refer-ence paths are largely decoupled from fluid motions of the remaining fluid volume. The pulse duration of the sound pulses is selected suitably to be less when the fili levels are less than when the fill levels are near a maximum allowable fill level. This is done by reducing the trans-mission voltage for the piezoceramic of the ultrasound test heads or sound pulse transmitters and receivers. ~t low charge voltages of the piezoceramic, the settling time and thus the time not available for echo detection is substan-tially shorter.
In a further feature of the invention, the fluid volume is determined either from the fill level h(T) or h (T), by multiplication by a factor taken for this purpose from a - : i- . . . : :: .
..:;. :
,: , : - ::
s tank characteristic curve, and from that, by multiplication ~y the density derived from the temperature distribution, the fluid quantity is determined.
The subject of the invention is also the use of a sound waveguide, as described in claims 8 and 9 as a T-shaped measuring tube combined from a longitudinal and a transverse tube, for accommodating and retaining not only one or more sound pulse transmitters and receivers but also the refer-ence reflectors or screens of a fill level measuring device, in which the reference reflectors or screens are disposed over the fill level height at a defined spacing from one another and from the sound pulse transmitters and receivers, and the ultrasound pulses reflected from the reference reflectors or screens produce transit time differences, which together with the associated known sound travel lengths are used to ascertain an average sound velocity in the fluid volume that takes the density in the fluid volume into account, wherein the fill level is ascertained from the average sound velocity and from the transit time differenc-es, referred to the surface of the fluid, of the ultrasound measurin~ beams.
For further explanation of the fill lsvel measuring device and of the associated method for determining the fill level .
, ,-~. . . .
according to the invention, several exemplary embodiments will be described below in conjunction with the drawing.
The drawing, in sometimes simplified, schematic form, shows the following:
Fig. 1, the tank of a tank installation, in frag~entary form and partially in section, which is provided with a fill level measuring device according to the invention;
Fig. 2, an outline of the tank installation of a service station, showing a somewhat modified tank that has a fill level measuring device of Fig. 1;
Fig. 3, a diagram for ascertaining the mean temperature TM
with three temperature sensors distributed over the fill level height;
Fig. ~, a diagram corresponding to Fig. 3, in which only two temperature sensors are used to ascertain the mean tempera-ture TM, because the fill level has dropped;
Fig. 5, a corresponding diagram, in which only the lowermost temperature sensor is used to determine TM, because of the low fill level;
:
Fig. 6, a block circuit diagram of the measured value transducers and evaluation electronics connected to them for a fill level measuring device according to the invention;
and Fig. 7, a modified fill level measuring device to illustrate the advantageous use of a T-shaped measurement tube, com-bined from a longitudinal and a transverse tube, in fill level measuring devices that work with reference reflectors or screens.
Fig. 1 shows a tank 20 having a cylindrical middle part 1 and slightly bulging, rounded end walls 2; only the end having the dome 3 is shown. The tank 20, as shown in further detail in Fig. 2, is buried in the ground, so that its top is for instance located 1 meter below the surface of the ground. The tank 20 is used for instance for temporary storage of mineral oil-based liquid fuels at service sta-tions. The dome 3 forms an access pipe and has a lid flange 21 with a dome lid 22. A fill tube 23 for the fluid 10 is ducted through the dome lid 2Z, and retained there, protrud-ing into the container interior. The tube 23 can also serve as an extraction tube. A first sound waveguide 4 extending over virtually the entire height of the tank iB introduced into the tank 20 through the dome 3. On its lower end, it -~6-- ; ~ ~ , `:,` -2~ 5 has a transverse tube 5 disposed approximately parallel to the tank bottom; this forms a second sound waveguide for a reference measuring path 11~ For a tank diameter D of approximately 3 m, both the first sound waveguide 4 and the second sound waveguide 5 (transverse tube) have an inside diameter of approximately 50 mm. The first sound waveguide 4 has openings 6 in its lower region, through which openings the interior of the tubes 4 and 5 communicates with the fluid 10 in the tank 20, so that by the principle of commu-nicating tubes, the same level 9' as the level or surface 9 of the remaining volume of fluid 10 is established in the first sound waveguide 4. The second sound waveguide 5 will henceforth be called the transverse tube, for simplicity.
It is provided with a sound hole 7 in the vicinity of one end, on the side toward the tank bottom.
The T-shaped unit of a measuring tube 24, comprising the vertical (first) sound waveguide 4 and the horizontal transverse tube 5, has three sound pulse transmitters and receivers S1, S2, S3.
The first sound pulse transmitter and receiver S1 is secured in the transverse tube 5 opposite the mouth of the first sound waveguide 4. In the direction of a double arrow 8 corresponding to a main measuring path, it sends and ,, , ~
2~ 5 receives sound pulses that are reflected from the surfac~ 9 of the fluid 10. The opening 6 in the first sound waveguide 4 assurPs that the level 9' of the fluid 10 inside the sound waveguide 4 will precisely match the level 9 of the fluid outside the sound waveguide 4, as already indicated.
Moreover, the considerable size of the sound waveguide 4 cross section assures that any departure in surface shape from the horizontal, due to sur~ace tension of the fluid 10, will be negligi~ly slight.
The second sound pulse transmitter and receivers S2 is supported by one end wall of the transverse tube 5. It sends and receives sound pulses in the direction of a double arrow 11 that are reflected by the opposite end wall of the transverse tube 5. Since the length of the transverse tube 5, as a reference path, is known with precision, the sound velocity inside the reference path 11, and with certain limitations the type of fluid 10, can be derived from the transit time of the sound pulses transmitted and received by the sound pulse transmitter and receiver S2.
The third sound pulse transmitter and receiver S3 is mounted opposite the sound hole 7 in the transverse tube 5. It transmits and receives in the direction of a vertical double arrow 12. As the first echo in each case, from every pulse `' `'''~' :
., .
transmitted, it receives the echo of a level 13, which is the boundary layer between the fluid lO and contaminants, such as water and dirt, that have settled to the bottom of the tank 20 because of their greater density.
In the fill level measuring device of Fig. 1, there are also temperature sensors 14, 15, 16, by way of which the fluid temperature is detected at the level of the transverse tube 5, and at the heights of one-third and two-thirds of the maximum allowable fill height of the tank 20. The tempera-ture sensor 14 is the reference temperature sensor for the reference path, represented by the double arrow 11. With it, a reference temperature TRef of the partial fluid volume of the reference path 11 can be measured. By means of the second sound pulse transmitter and receiver S2, the sound velocity v (TRef) for the fluid volume at the reference temperature (TRef) is also ascertained, on the basis of an applicable measured transit time difference ~t. For the known length of the reference path 11 and at the measured reference temperature TRef, the result is the sound velocity v (TRef). The reference path 11 is also used to ascertain a correction factor Kk, which is used to calculate an average or temperature-corrected sound velocity from the reference sound velocity v . This correction factor is defined as follows:
~.,, ' :
., ,, , , ~ , 1 v(Tl) - v(To) k ~T v(To) In this e~uation, ~T is defined by the difference T 1 -To ;
Tl, To are two different temperatures of the fluid 10, measured at the reference path 11 with the reference temper-ature sensor 14, and v(T1), v (To) are the associated sound velocities measured using the reference path. The correc-tion factor, or more generally the correction function Xk, on the basis of the measurements o~ Tl, Tol v(T1), v(To)/
indicates the stan~ardized variation of the sound velocity per degree of temperature variation of the fluid volume 10.
The temperature-corrected fill level is ascertained in accordance with the equation h (T) = v (T) tH~ in which tH
is the portion of the transit time difference ~t 1 corre-sponding to the fill level, that is measured with the first sound pu~se transmitter and receiver S1. If the measurement beam makes only one round trip, as shown, then tH = ~ /2.
To ascertain the temperature-corrected sound velocity v(T) for the entire fluid volume, the following basic equation is used:
v(T) = v (TRef) ~ Kk ~T].
-2~-, . :
z~
In this equation, all the variables are known, except for ~T
= TM - TRef, where TM is the mean temperature TM in the fluid volume; means are provided or determining this temper-ature, in the form of the temperature sensors 14, 15 and 16 already mentioned, for detecting the temperature distribu-tion over the fill level height h. With these temperature sensors, of which the reference temperature sensor 14 is used not only to ascertain the re~erence temperature TRef but also - along with the other two temperature sensors -for measuring the temperature distribution over the fill level height, the mean temperature TM of the fluid volume can be ascertained relatively accurately, as will be de-scribed below in conjunction with Figs. 3-5.
In Fig. 3, the fill height h (on the ordinate) is plotted over the temperature axis T (on the abscissa). HU is the height or vertical position of the lower temperature sensor 14, which measures the temperature TSU. HM is the height of the mean temperature sensor 15, which is capab~e of measur-ing the temperature TSM; TSM is greater than TSU. HO is the height of the upper temperature sensor 1~, which is capable of measuring the temperature T50; TSO is greater than TSM.
Figs. 3-5 are based on a graduated averaging process. On the basis of the disposition of three temperature sensors, : . -.......... . :, . , . - ; :
:- : ., . ~: ;:
.
distributed over the fill height, three possible cases ~or the fluid level (gasoline level) in the tank 20 should be taken into account; an installation tolerance for the particular temperature sensor has been added to the height indications H0, HM, HU, in order to assure that any sensor that is not immersed in the fluid will not be used for the temperature averaging. The three possible cases are as follows:
1. The fill height h = H1; that is, it is higher or sub-stantially higher than 1, or in other words is higher or substantially higher than the installed height H0 of the temperature sensor 16; see Fig. 3.
2. The fill height h = H2; that is, it is located between HM tmiddle height of the sensor 15) and ~0 (installation height of the upper temperature sensor); see Fig. 4 in combination with Fig. 3.
factor that on the basis of the measurements of T1, To~
v(Tl~ ~ v(To) indicates the standardized variation in the sound velocity per deyree of temperature variation of the fluid volume, and wherein further tH is the portion of the transit time difference ~t1 corresponding to the fill level height, which difference is measured with each of the first sound pulse transmitters and receivers (S1).
Advantageous features of the fill level measuring device are disclosed in claims 2-15.
The advantages attainable with the invention are above all that no reference reflectors are disposed in the way of the main measuring path; consequently the ultrasound signal transmitted to the surface of the fluid and sent back by it reaches the sound pulse receiver practically unhindered.
The means for temperature distribution over the fill level ~-height need not be located in the cone formed by the beams of the main measuring path, but can instead be located laterally thereof.
The means for detecting the temperature distribution, according to claim 2, preferably includes temperature sensors, which are disposed in a plurality of measuring points distributed over the fill level height, and from the :, , ., ~ , . . .
' ~r~ s temperature measurement values of which the mean temperature TM of the fluid volume can be derived by averaging. It was already possible to attain very good measuring results with a fill level measuring device according to claim 3, in which the means for detecting the temperature distribution include at least one temperature sensor, disposed in the vicinity of the bottom, and at approximately one-third and approximately two-thirds of the maximum fill level of the container.
The temperature sensors are preferably secured to the outer circumference of a sound waveguide, which is described in detail in claims 4-11. For the main measuring path, accord-ing to claim 4, a vertically aligned sound waveguide is provided that extends from the bottom region of the contain-er up to a height that is located above the maximum fill level. The interior of this first sound waveguide communi-cates via openings with the remaining fluid volume. On its lower end, there is a sound pulse transmitter for transmit-ting an ultrasound beam in the direction of the surface of the fluid volume, and a first sound pulse receiver for receiving the ultrasound beam reflected from the surface.
The temperature sensor~ are preferably secur~d to the outside of this first sound wavPguide, as mentioned.
According to claim 6, the reference path is assigned its own second sound waveguide, to which the ~ound pulse transmitter .: ~
- ' '```' and receiver and the at least one reference temperature sensor are secured, and the interior of which communicates with the remaining fluid volume via at least one opening.
It is favorable if the second sound waveguide for the reference path is embodied as a transverse tube disposed near the bottom of the container (claim 7). A compact measurement array that is easy to mount is attained by means of a combined sound waveguide in accordance with claim 8, in which the first sound waveguide for the main measuring path is structurally united on its lower end with the transverse tube for the reference path, to make a T-shaped, continuous-ly hollow measurement tube.
Other advantageous features of the combined sound waveguide, in particular relating to the disposition of the first sound pulse transmitter and receiver and further, third sound pulse transmitters and receivers, for ascertaining the sump level, are disclosed in claims 9-11.
An advantageous fastening of the first sound waveguide or of the combined sound waveguide to a fill tube passed through the container dome lid, and the laying of the measuring and current supply lines and their ducting through the dome lid are recited in claim 12.
.
~ ~ , Piezoceramic sensors are preferably used as the sound pulse transmitters and receivers for the fill level measuring device; suitably, their sound transit times are each mea-sured from the moment the sensor short circuits until the first amplitude of an echo arrives (claim 13). Good mea-surement accuracy with measured value tolerances of less than 1 mm are obtained if counting pulses specified in a fixed rhythm are used to detect the sound transit times of a transit time counter oscillator, and if the frequency of the transmitted ultrasound pulses are in a ratio of 1:3 to 1:6 with the frequency of the transit time counter oscillator (claim 14). According to claim 15, it is especially favor-able if the frequency of the transmitted ultrasound pulses is 2 MHz and that of the transit time counter oscillator is 8 MHz.
The subject of the invention is also a method for determin-ing the fill level in containers filied with fluid, pre~era-bly in tanks of tank installations, with determination of the fill level from the sound transit time of ultrasound pulses, which are emitted along a main measuring path, extendlng from the bottom region of the container to the surface of the fluid, by first sound pulse transmitters and are reflected from the surface of the fluid to first sound pulse receivers.
, ~
:, , ,' ;:,,' . '~. :
'~
This generic method, which is likewise known from the European Patent Document A3 0 106 677 mentioned at the outset, is intended to be embodied, analogously to the fill level measuring device according to the invention, in which a wa~ that it is unnecessary to work with a multiplicity of reference measuring beams that are transmitted by a sound pulse transmitter and after being reflected from the refer-ence reflectors are received by a sound pulse receivers and carried further for further processing. Instead, the method according to the invention should enable ascertaining the fill level at least equally accurately, if not even more accurately, in proportion to the electrical, mechanical and electronic expenditure, without using reference reflectors.
To attain this object, the method according to the invention is characterized in that a temperature-corrected sound velocity vtT) in the fluid volume is ascertained in accor-dance with the following equation:
v(T) = v (TRef) [1 + Kk ]
and from that a temperature-corrected fill level h(T) = v(T) tH
is ascertained, in which the correction factor Kk is defined by the following equation:
Kk = 1 v(Tl) - v(To) ~TV (T o ) , ,. ,~ , . - . - :
, : . . . ` ` ~:: `
:~ ` , ': , ;
2~ s wherein ~T = Tl - To ~ T = T - T
and in which the following symbols have the following meanings:
TM, the mean temperature of the fluid volume derived by measuring the temperature at a plurality of measurement points distributed over the fill level height;
v , the sound velocity, ascertained at the reference temper-ature TRef along a reference path of known length located in the fluid volume, this velocity being derived from the transit time differences of the ultrasound pulses that ensue between a second sound pulse transmitter and a second sound pulse receiver at the beginning and end of the reference path, respectively;
TRef, the reference temperature at the reference path at the time of the particular transit time measurement;
T1, To~ the different temperatures of the fluid, measured at the reference path;
v(Tl) ~ v(To) ~ the associated sound velocities ascertained with the reference path;
Kk, a medium-specific correction factor, which indicates the standardized variation in the sound velocity per degree of temperature variation of the fluid volume; and tH~ the portion of the transit time difference ~t 1 ~ corre-sponding to the fill level, that is measured with the first sound pulse transmitters and receivers (S1), respectively.
Advantageous further features of this method are disclosed in claims 17-21.
The advantages attainable with this method are considered above all to be that for every fill level measurement, a current correction factor is determined, even whenever there is no linear relationship between the variation in sound velocity as a function of the temperature variation of the fluid volume. This advantage also applies to the fill level measuring device of the invention. The mean temperature TM
can be determined very accurately, as will be explained in further detail hereinafter, by measuring the temperature at a plurality of measuring points distributed over the fill level height.
- , . . . . . ~
.
! ;, i. .
z~
For the practical application of the method, it is es~ecial-ly advantageous if according to claim 16, in the ascertain-ment Gf the fill level height h(T), the sump height b in the container is also taken into account, and that the fill level height h (T) taking the sump height into account is ascertained in accordance with the following equation:
h (T) = tH v(T) + ts v(T) - a + b, wherein the following symbols have the following meanings:
tS, the portion of the transit time difference ~t S corre-sponding to the sump height, which is measured with a third sound pulse transmitter and receiver (S3), which is disposed in the region near the bottom of the fluid volume;
a, the distance, measured vertically between the flrst and third sound pulse transmitters and receivers (S1-S3), and b, the sump height measured by the third sound pulse trans-mitters and receivers (S3).
It is favorable to amplify the sound pulses, received by the sound pulse receivers, as a function of the sound transit time, in order to keep relatively constant for both short and longer transit times of the first amplitude.
. ; . , : ; .
.
.
x~
In combinatio~ with the main measuring path extending inside a sound waveguide, it is especially advantageous that feedback from surface motion of the fluid upon the fill level is minimized by the sound waveguide itself and by multiple measurements. Since the first second sound waveguides, or the measuring tube formed by the combination of the two, communicates with the fluid volume via openings, provision is made on the one hand for a temperature balance within the main measuring path and the reference measuring path and the remaining fluid volume; on the other hand, this avoids so-called sound drifts, because the main and refer-ence paths are largely decoupled from fluid motions of the remaining fluid volume. The pulse duration of the sound pulses is selected suitably to be less when the fili levels are less than when the fill levels are near a maximum allowable fill level. This is done by reducing the trans-mission voltage for the piezoceramic of the ultrasound test heads or sound pulse transmitters and receivers. ~t low charge voltages of the piezoceramic, the settling time and thus the time not available for echo detection is substan-tially shorter.
In a further feature of the invention, the fluid volume is determined either from the fill level h(T) or h (T), by multiplication by a factor taken for this purpose from a - : i- . . . : :: .
..:;. :
,: , : - ::
s tank characteristic curve, and from that, by multiplication ~y the density derived from the temperature distribution, the fluid quantity is determined.
The subject of the invention is also the use of a sound waveguide, as described in claims 8 and 9 as a T-shaped measuring tube combined from a longitudinal and a transverse tube, for accommodating and retaining not only one or more sound pulse transmitters and receivers but also the refer-ence reflectors or screens of a fill level measuring device, in which the reference reflectors or screens are disposed over the fill level height at a defined spacing from one another and from the sound pulse transmitters and receivers, and the ultrasound pulses reflected from the reference reflectors or screens produce transit time differences, which together with the associated known sound travel lengths are used to ascertain an average sound velocity in the fluid volume that takes the density in the fluid volume into account, wherein the fill level is ascertained from the average sound velocity and from the transit time differenc-es, referred to the surface of the fluid, of the ultrasound measurin~ beams.
For further explanation of the fill lsvel measuring device and of the associated method for determining the fill level .
, ,-~. . . .
according to the invention, several exemplary embodiments will be described below in conjunction with the drawing.
The drawing, in sometimes simplified, schematic form, shows the following:
Fig. 1, the tank of a tank installation, in frag~entary form and partially in section, which is provided with a fill level measuring device according to the invention;
Fig. 2, an outline of the tank installation of a service station, showing a somewhat modified tank that has a fill level measuring device of Fig. 1;
Fig. 3, a diagram for ascertaining the mean temperature TM
with three temperature sensors distributed over the fill level height;
Fig. ~, a diagram corresponding to Fig. 3, in which only two temperature sensors are used to ascertain the mean tempera-ture TM, because the fill level has dropped;
Fig. 5, a corresponding diagram, in which only the lowermost temperature sensor is used to determine TM, because of the low fill level;
:
Fig. 6, a block circuit diagram of the measured value transducers and evaluation electronics connected to them for a fill level measuring device according to the invention;
and Fig. 7, a modified fill level measuring device to illustrate the advantageous use of a T-shaped measurement tube, com-bined from a longitudinal and a transverse tube, in fill level measuring devices that work with reference reflectors or screens.
Fig. 1 shows a tank 20 having a cylindrical middle part 1 and slightly bulging, rounded end walls 2; only the end having the dome 3 is shown. The tank 20, as shown in further detail in Fig. 2, is buried in the ground, so that its top is for instance located 1 meter below the surface of the ground. The tank 20 is used for instance for temporary storage of mineral oil-based liquid fuels at service sta-tions. The dome 3 forms an access pipe and has a lid flange 21 with a dome lid 22. A fill tube 23 for the fluid 10 is ducted through the dome lid 2Z, and retained there, protrud-ing into the container interior. The tube 23 can also serve as an extraction tube. A first sound waveguide 4 extending over virtually the entire height of the tank iB introduced into the tank 20 through the dome 3. On its lower end, it -~6-- ; ~ ~ , `:,` -2~ 5 has a transverse tube 5 disposed approximately parallel to the tank bottom; this forms a second sound waveguide for a reference measuring path 11~ For a tank diameter D of approximately 3 m, both the first sound waveguide 4 and the second sound waveguide 5 (transverse tube) have an inside diameter of approximately 50 mm. The first sound waveguide 4 has openings 6 in its lower region, through which openings the interior of the tubes 4 and 5 communicates with the fluid 10 in the tank 20, so that by the principle of commu-nicating tubes, the same level 9' as the level or surface 9 of the remaining volume of fluid 10 is established in the first sound waveguide 4. The second sound waveguide 5 will henceforth be called the transverse tube, for simplicity.
It is provided with a sound hole 7 in the vicinity of one end, on the side toward the tank bottom.
The T-shaped unit of a measuring tube 24, comprising the vertical (first) sound waveguide 4 and the horizontal transverse tube 5, has three sound pulse transmitters and receivers S1, S2, S3.
The first sound pulse transmitter and receiver S1 is secured in the transverse tube 5 opposite the mouth of the first sound waveguide 4. In the direction of a double arrow 8 corresponding to a main measuring path, it sends and ,, , ~
2~ 5 receives sound pulses that are reflected from the surfac~ 9 of the fluid 10. The opening 6 in the first sound waveguide 4 assurPs that the level 9' of the fluid 10 inside the sound waveguide 4 will precisely match the level 9 of the fluid outside the sound waveguide 4, as already indicated.
Moreover, the considerable size of the sound waveguide 4 cross section assures that any departure in surface shape from the horizontal, due to sur~ace tension of the fluid 10, will be negligi~ly slight.
The second sound pulse transmitter and receivers S2 is supported by one end wall of the transverse tube 5. It sends and receives sound pulses in the direction of a double arrow 11 that are reflected by the opposite end wall of the transverse tube 5. Since the length of the transverse tube 5, as a reference path, is known with precision, the sound velocity inside the reference path 11, and with certain limitations the type of fluid 10, can be derived from the transit time of the sound pulses transmitted and received by the sound pulse transmitter and receiver S2.
The third sound pulse transmitter and receiver S3 is mounted opposite the sound hole 7 in the transverse tube 5. It transmits and receives in the direction of a vertical double arrow 12. As the first echo in each case, from every pulse `' `'''~' :
., .
transmitted, it receives the echo of a level 13, which is the boundary layer between the fluid lO and contaminants, such as water and dirt, that have settled to the bottom of the tank 20 because of their greater density.
In the fill level measuring device of Fig. 1, there are also temperature sensors 14, 15, 16, by way of which the fluid temperature is detected at the level of the transverse tube 5, and at the heights of one-third and two-thirds of the maximum allowable fill height of the tank 20. The tempera-ture sensor 14 is the reference temperature sensor for the reference path, represented by the double arrow 11. With it, a reference temperature TRef of the partial fluid volume of the reference path 11 can be measured. By means of the second sound pulse transmitter and receiver S2, the sound velocity v (TRef) for the fluid volume at the reference temperature (TRef) is also ascertained, on the basis of an applicable measured transit time difference ~t. For the known length of the reference path 11 and at the measured reference temperature TRef, the result is the sound velocity v (TRef). The reference path 11 is also used to ascertain a correction factor Kk, which is used to calculate an average or temperature-corrected sound velocity from the reference sound velocity v . This correction factor is defined as follows:
~.,, ' :
., ,, , , ~ , 1 v(Tl) - v(To) k ~T v(To) In this e~uation, ~T is defined by the difference T 1 -To ;
Tl, To are two different temperatures of the fluid 10, measured at the reference path 11 with the reference temper-ature sensor 14, and v(T1), v (To) are the associated sound velocities measured using the reference path. The correc-tion factor, or more generally the correction function Xk, on the basis of the measurements o~ Tl, Tol v(T1), v(To)/
indicates the stan~ardized variation of the sound velocity per degree of temperature variation of the fluid volume 10.
The temperature-corrected fill level is ascertained in accordance with the equation h (T) = v (T) tH~ in which tH
is the portion of the transit time difference ~t 1 corre-sponding to the fill level, that is measured with the first sound pu~se transmitter and receiver S1. If the measurement beam makes only one round trip, as shown, then tH = ~ /2.
To ascertain the temperature-corrected sound velocity v(T) for the entire fluid volume, the following basic equation is used:
v(T) = v (TRef) ~ Kk ~T].
-2~-, . :
z~
In this equation, all the variables are known, except for ~T
= TM - TRef, where TM is the mean temperature TM in the fluid volume; means are provided or determining this temper-ature, in the form of the temperature sensors 14, 15 and 16 already mentioned, for detecting the temperature distribu-tion over the fill level height h. With these temperature sensors, of which the reference temperature sensor 14 is used not only to ascertain the re~erence temperature TRef but also - along with the other two temperature sensors -for measuring the temperature distribution over the fill level height, the mean temperature TM of the fluid volume can be ascertained relatively accurately, as will be de-scribed below in conjunction with Figs. 3-5.
In Fig. 3, the fill height h (on the ordinate) is plotted over the temperature axis T (on the abscissa). HU is the height or vertical position of the lower temperature sensor 14, which measures the temperature TSU. HM is the height of the mean temperature sensor 15, which is capab~e of measur-ing the temperature TSM; TSM is greater than TSU. HO is the height of the upper temperature sensor 1~, which is capable of measuring the temperature T50; TSO is greater than TSM.
Figs. 3-5 are based on a graduated averaging process. On the basis of the disposition of three temperature sensors, : . -.......... . :, . , . - ; :
:- : ., . ~: ;:
.
distributed over the fill height, three possible cases ~or the fluid level (gasoline level) in the tank 20 should be taken into account; an installation tolerance for the particular temperature sensor has been added to the height indications H0, HM, HU, in order to assure that any sensor that is not immersed in the fluid will not be used for the temperature averaging. The three possible cases are as follows:
1. The fill height h = H1; that is, it is higher or sub-stantially higher than 1, or in other words is higher or substantially higher than the installed height H0 of the temperature sensor 16; see Fig. 3.
2. The fill height h = H2; that is, it is located between HM tmiddle height of the sensor 15) and ~0 (installation height of the upper temperature sensor); see Fig. 4 in combination with Fig. 3.
3. The fill height h = H3; that is, it is located below the installed height HM of the middle temperature sensor 15, so that only the lower temperature sensor 14 is used for measurement (see Fig. 5 in combination with Fig. 3)~
The formula "TM 1" pertains for case (1):
~ ' , ' ' ~
, ~1, ' ' . ~ - .
2~ 5 TM = 1 [I ~ + (~-HU) TSM + ~ ], ) I
area A s C
the formula "TM 2" applies to case t2):
TM = 1 r (H2 ~ HM+HU) TSM + (HM+HU~ TSU 1, area A' B' and the formula TM 3 applies for the simplest case (3):
TM = TSU.
Briefly, in case (1), the areas A (diagonal shading from bottom left to top right), B (diagonal shading from top left to bottom right) and C (crosshatching) are added together and then divided by the entire fill level height of the applicable case, in this case H1, the result then being the mean temperature TM (formula TM 1). Case (2) is somewhat simpler, because only the areas A' and B' need to be added, the resulting area (A' ~ B') is then divided by the applica-ble fill lev~l height H2, in order to obtain TM. Case (3) is the simplest, because at this fill level height ~3, the temperature TSU measured by the bottom temperature sensor 1 then simultaneously represents the mean temperature TM.
The graduated averaging described above is relatively simple and produces relatively accurate results. The accuracy can .. . . .. .. ..
: .
; . .:
~r~ s be further increased if needed by installing additional -temperature sensors, for instance an additional fourth and perhaps fifth temperature sensor. TM could also be ascer-tained by linear averaging, rather than a graduated averag-ing process. In that process, a straight line would be drawn connecting the points 14 and 15 in Fig. 3, and another straight line would be drawn connecting point 15 and point 16. A calculation of the portion of the area for the areas formed between the straight lines and the ordinate axis would then be made, and the resulting area would be divided by the entire fill level height. However, in terms of its formula, this process is not as simple as the graduated averaging explained above. Graduated averaging is also superior to so-called curved averaging, in which the points 14, 15 and 16 are connected by a parabola.
To return to Fig. 1: It can be seen that the temperature sensors 15 and 16 are secured to the outside of the first sound waveguide 4. As a result, the source of sound for the main measuring path 8 is not affected or impaired. The measuring tube 24 and the first sound waveguide ~ are retained on the fill tube 23, axially parallPl to its longitudinal axis. The measurement and current supply lines 25 of the temperature sensors 14, 15, 16 and sound pulse transmitters and receivers S1, S2, S3 are laid on the ~ . , , :: , . . .
, . :
, ' ~s~
outside of the first sound waveguide, as the drawing shows, and are ducted to the outside through a gas-tight line duct 26 in the dome lid 22. The measurement and current supply lines 25 are shown merely schematically or in dashed lines in the lower region of the measuring tube 24. In the form of a bundle of lines, they are retained on the first sound waveguide 4 by means of cable clamps 27. The sound waveguide is secured to the fill tube 23 in a vertically aligned position by means of adjustable double clamps 28, as shown. Fig. 1 also schematically shows an evaluation uni~
29, which is connected via measurement amplifiers, not shown in Fig. 1, to the measurement and current supply lines 25 and which has a display field 30 that indicates a fill level of 1710 mm, for instance, and an average temperature TM of 49C.
Fig. 2 shows a complete tank installation 31 with a dome shaft 32 that is embodied by masonry 33 and is covered toward the outside in a functionally secure manner by a hatch 34 in the form of a steel plate or the like. The dome 3 of the tank 20 i5 accessible via the dome shaft 32. The tank is embodied substantially like the tank 20 of Fig. 1 and also has a corresponding fill level measuring device. A
control panel 35 for an electronic measurement unit to which the measurement and current supply lines 25 are laid is ,;
, :
disposed on the inside circumference of the dome sha~t 32.
The control panel 35 suitably includes measurement amplifi-ers and a lightning protection unit. In this context it should be mentioned that the cable duct 26 is embodied as flashback-proof. A connecting cable 36 is laid from the control box for the measuring electronic unit through the ground at a depth of approximately 1 m (so that it is protected against frost), in a cable conduit 37, as far as a control unit 39 disposed in the building 38. A maximum of eight connecting lines 40, by way of example, lead from this control unit 3g to other tanks (not shown), and a data line 41 also leads to a computer that is used for measurement data processing. The foundation of the tank installation, on which the gas pumps 42 and the building 38 are located, is identified by reference numeral 43; the connecting cable 36 to the control unit 39 in the building 38 is ducted through this foundation, or pavement. 44 schematically indicates the ground in which the tank 20 is located.
The block cir~uit diagram of Fig. 6 shows the electronic components of a fill level measuring device according to the invention. The box 45 encloses the two component units 46 of the so-called level sensors, that is, the sound pulse transmitters and receivers S1, S2, S3, and the component unit 47 comprising the temperature sensors 14, 15, 16. The , - ~ : -:
.
- . ,~
:
, i : :
2C?~5~
component units 46, 47, via signal and current supply lines shown schematically at 25, communicate with an ultrasound control and supply unit 48, on the one hand, and a tempera-ture measurement signal evaluation unit 49, on the other.
The unit 48 includes the "sensor triggering and echo signal reception" subunit 50, "sensor signal amplifier" 51, and "sensor signal digitizing" subunit 52. A computer and voltage regulator unit 53 is also provided, including the "microprocessor control" subunit 54, "microprocessor evalua-tion" 55, "measurement data output" 56, and "voltage regula-tor" 57. 58 indicates a power supply unit, which is elec-trically connected to the voltage regulator 57 via a multi-ple-conductor current supply and signal cable 59. Addition-al measurement and control lines lead in the form o~ a line 60 from the microprocessor control 54 to the component unit 5Q, and from that a line 61 leads to the component unit 51, -from which a line 62 leads to the computer unit 52, from which again a line 63 leads to the microprocessor evaluation component 55. This last unit 55 is connected for dialog, via the lines 64a, 64b, to the measurement data output 5~, -and tha microprocessor control 54 is connected with the microprocessor evaluation unit 55 via a data line 65. From the voltage regulator 57, a supply line 6Ç leads to the "m~asurement data output" unit 56, and from that unit an electrical signal line 67 i~ fed back to the input of the 2~ 5 voltage regulator 57 or to the connecting line 59. Via the signal line 68, the processed temperature measurement signals TM, ~T , ~T reach the "measurement data output"
unit 56. With the component unit 47, the measured values To~ T1, TSU, TSM, TSO that are needed to calculate the mean temperature TM can be ascertained.
Piezoceramic sensors are preferably used as the sound pulse transmitters and sound pulse receivers S1, S2, S3; the sound transit times in each case are measured from the instant of sensor short circuit until the arrival of the first ampli-tude of an echo. A piezoceramic wafer that is glued into a housiny, preferably of stainless steel or plastic, in such a way that the housing thickness of the side of the sensor toward the filling medium is adapted to the wavelength of ultrasound (multiples of ~/4, preferably ~/2) is used as the basic component of such sensors. The component unit 50 contains transit time counter oscillators, which to detect the sound transit times produce predetermined counting pulses at a fixed rhythm; the frequency of the ultrasound pulses transmitted by the sound pulse transmitters S1-S3 is preferably in a ratio of 1:3 to 1:6 to the frequency of the transit time counter oscillator. For the sake of high basic measurement accuracy, the resonant and operating ~requency is set to 2 MHz, which in water is equivalent to a s wavelength of 0.75 mm. The transit time counter oscillator preferably has an operating frequancy of 8 MHz.
For the temperature sensors 14-16, a differential measure-ment accuracy of approximately one-tenth of a degree is provided, so that even relatively small temperature gradi-ents within the tank 20 can be detected.
A method for determining the fill level in containers filled with fluid, preferably in tanks of tank installations, is achieved with the fill level measuring device explained above in conjunction with Figs. 1-6. In this method, the fill level height is from the sound transit time of ultrasound pulses that are projected along a main measuring path 8, extending from the bottom region of the container 20 up to the surface 9 of the fluid, by first sound pulse ``transmitters Sl and reflected from the surface g of the fluid to first sound pulse receivers (likewise S1, because transmit-receive test heads are used).
A temperature-corrected sound velocity v(T) - see component 55 of Fig. 6 - in the fluid volume is ascertained in accor-dance with the following equation:
v(T) = V (TRef) [1 ~ k ]
. .
~, :
, ..
;
~: .
2~ s From this, a temperature-corrected fill level height h~T) =
v(T) t~ is ascertained, in which the correction factor Kk is defined as described above. To ascertain the correction factor Kk, the reference path 11, with which the values vtTl) ~ v(To), Tl, To and the reference temperature TRef are measured, is used, as also already explained. From the mean temperature TM found by averaging, ~T = TM - T Ref can then be ascertained, and the temperature difference ~T can be ascertained from the difference Tl - To~ The components 49 and 55 are used to ascertain the derived variables.
In ascertaining the fill level height h(T), the sump height b in the container or tank 20 is preferably used as well.
The fill level height h (T) that takes the sump height b into account is ascertained by the following squation:
h (T) - tH v(T) + ts v(T) - a + b.
This equation and the variables it contains have already been explained previously above.
When the method is carried out, the sound pulses picked up by the sound pulse receivers Sl, S2, S3 are suitably ampli-fied as a function of the sound transit time. This opera-tion is performed in the component 51 (Fig. 6). The ultrasound reception signals are then digitized in the next stage 52, before they are carried to the evaluation , ~ -30-.
component 55 of the microprocessor. In this evaluation unit 55, the fluid volume can also be determined, on the basis of the ascertained fill level height h(T), or preferably h (T), by multiplication by a factor taken from a tank characteris-tic curve (not shown), and from that, by multiplication with the density derived from the temperature distribution, the fluid quantity can be determined. The pulse duration of the sound pulses is selected suitably to be less at low fill heights than at fill heights near a maximum allowable fill height, as already explained. When the method is carried out, the measuring tube 24 has an advantageous effect in the sense that feedback from surface motions of the fluid 10 on the fill level in the first sound waveguide 4 can be mini-mized by this waveguide itself and by multiple measurements.
Fiy. 7 also serves to illustrate an advantageous use. In this drawing, which is simplified compared with Fig. 1, measuring screens or reference reflectors 17, 18, distribut-ed over the fill level height, are installed on the inside circumference of the first sound waveguide 4. The measuring tube shown here, and identified as a whole by reference numeral 24, and which is again a combination of the ~irst and second sound waveguides, serves to accommodate and retain one or more sound pulse transmitters and receivers Sl, S2, S3 and the reference reflectors 17 and 18 of a fill level measuring device, in which the reference reflectors are disposed over the fill level height at a defined spacing from one another and from the sound pulse transmitters and receivers S1; the ultrasound pulses reflected by the refer-ence reflectors 17, 18 produce transit time differences, which together with the associated, known sound travel distances, enable the ascertainment of an average sound velocity that talces the density in the fluid volume 10 into account. From the average sound velocity and from the transit time difference, referred to the fluid surface, of the applicable ultrasound measurement beams, the fill level height can be ascertained.
,
The formula "TM 1" pertains for case (1):
~ ' , ' ' ~
, ~1, ' ' . ~ - .
2~ 5 TM = 1 [I ~ + (~-HU) TSM + ~ ], ) I
area A s C
the formula "TM 2" applies to case t2):
TM = 1 r (H2 ~ HM+HU) TSM + (HM+HU~ TSU 1, area A' B' and the formula TM 3 applies for the simplest case (3):
TM = TSU.
Briefly, in case (1), the areas A (diagonal shading from bottom left to top right), B (diagonal shading from top left to bottom right) and C (crosshatching) are added together and then divided by the entire fill level height of the applicable case, in this case H1, the result then being the mean temperature TM (formula TM 1). Case (2) is somewhat simpler, because only the areas A' and B' need to be added, the resulting area (A' ~ B') is then divided by the applica-ble fill lev~l height H2, in order to obtain TM. Case (3) is the simplest, because at this fill level height ~3, the temperature TSU measured by the bottom temperature sensor 1 then simultaneously represents the mean temperature TM.
The graduated averaging described above is relatively simple and produces relatively accurate results. The accuracy can .. . . .. .. ..
: .
; . .:
~r~ s be further increased if needed by installing additional -temperature sensors, for instance an additional fourth and perhaps fifth temperature sensor. TM could also be ascer-tained by linear averaging, rather than a graduated averag-ing process. In that process, a straight line would be drawn connecting the points 14 and 15 in Fig. 3, and another straight line would be drawn connecting point 15 and point 16. A calculation of the portion of the area for the areas formed between the straight lines and the ordinate axis would then be made, and the resulting area would be divided by the entire fill level height. However, in terms of its formula, this process is not as simple as the graduated averaging explained above. Graduated averaging is also superior to so-called curved averaging, in which the points 14, 15 and 16 are connected by a parabola.
To return to Fig. 1: It can be seen that the temperature sensors 15 and 16 are secured to the outside of the first sound waveguide 4. As a result, the source of sound for the main measuring path 8 is not affected or impaired. The measuring tube 24 and the first sound waveguide ~ are retained on the fill tube 23, axially parallPl to its longitudinal axis. The measurement and current supply lines 25 of the temperature sensors 14, 15, 16 and sound pulse transmitters and receivers S1, S2, S3 are laid on the ~ . , , :: , . . .
, . :
, ' ~s~
outside of the first sound waveguide, as the drawing shows, and are ducted to the outside through a gas-tight line duct 26 in the dome lid 22. The measurement and current supply lines 25 are shown merely schematically or in dashed lines in the lower region of the measuring tube 24. In the form of a bundle of lines, they are retained on the first sound waveguide 4 by means of cable clamps 27. The sound waveguide is secured to the fill tube 23 in a vertically aligned position by means of adjustable double clamps 28, as shown. Fig. 1 also schematically shows an evaluation uni~
29, which is connected via measurement amplifiers, not shown in Fig. 1, to the measurement and current supply lines 25 and which has a display field 30 that indicates a fill level of 1710 mm, for instance, and an average temperature TM of 49C.
Fig. 2 shows a complete tank installation 31 with a dome shaft 32 that is embodied by masonry 33 and is covered toward the outside in a functionally secure manner by a hatch 34 in the form of a steel plate or the like. The dome 3 of the tank 20 i5 accessible via the dome shaft 32. The tank is embodied substantially like the tank 20 of Fig. 1 and also has a corresponding fill level measuring device. A
control panel 35 for an electronic measurement unit to which the measurement and current supply lines 25 are laid is ,;
, :
disposed on the inside circumference of the dome sha~t 32.
The control panel 35 suitably includes measurement amplifi-ers and a lightning protection unit. In this context it should be mentioned that the cable duct 26 is embodied as flashback-proof. A connecting cable 36 is laid from the control box for the measuring electronic unit through the ground at a depth of approximately 1 m (so that it is protected against frost), in a cable conduit 37, as far as a control unit 39 disposed in the building 38. A maximum of eight connecting lines 40, by way of example, lead from this control unit 3g to other tanks (not shown), and a data line 41 also leads to a computer that is used for measurement data processing. The foundation of the tank installation, on which the gas pumps 42 and the building 38 are located, is identified by reference numeral 43; the connecting cable 36 to the control unit 39 in the building 38 is ducted through this foundation, or pavement. 44 schematically indicates the ground in which the tank 20 is located.
The block cir~uit diagram of Fig. 6 shows the electronic components of a fill level measuring device according to the invention. The box 45 encloses the two component units 46 of the so-called level sensors, that is, the sound pulse transmitters and receivers S1, S2, S3, and the component unit 47 comprising the temperature sensors 14, 15, 16. The , - ~ : -:
.
- . ,~
:
, i : :
2C?~5~
component units 46, 47, via signal and current supply lines shown schematically at 25, communicate with an ultrasound control and supply unit 48, on the one hand, and a tempera-ture measurement signal evaluation unit 49, on the other.
The unit 48 includes the "sensor triggering and echo signal reception" subunit 50, "sensor signal amplifier" 51, and "sensor signal digitizing" subunit 52. A computer and voltage regulator unit 53 is also provided, including the "microprocessor control" subunit 54, "microprocessor evalua-tion" 55, "measurement data output" 56, and "voltage regula-tor" 57. 58 indicates a power supply unit, which is elec-trically connected to the voltage regulator 57 via a multi-ple-conductor current supply and signal cable 59. Addition-al measurement and control lines lead in the form o~ a line 60 from the microprocessor control 54 to the component unit 5Q, and from that a line 61 leads to the component unit 51, -from which a line 62 leads to the computer unit 52, from which again a line 63 leads to the microprocessor evaluation component 55. This last unit 55 is connected for dialog, via the lines 64a, 64b, to the measurement data output 5~, -and tha microprocessor control 54 is connected with the microprocessor evaluation unit 55 via a data line 65. From the voltage regulator 57, a supply line 6Ç leads to the "m~asurement data output" unit 56, and from that unit an electrical signal line 67 i~ fed back to the input of the 2~ 5 voltage regulator 57 or to the connecting line 59. Via the signal line 68, the processed temperature measurement signals TM, ~T , ~T reach the "measurement data output"
unit 56. With the component unit 47, the measured values To~ T1, TSU, TSM, TSO that are needed to calculate the mean temperature TM can be ascertained.
Piezoceramic sensors are preferably used as the sound pulse transmitters and sound pulse receivers S1, S2, S3; the sound transit times in each case are measured from the instant of sensor short circuit until the arrival of the first ampli-tude of an echo. A piezoceramic wafer that is glued into a housiny, preferably of stainless steel or plastic, in such a way that the housing thickness of the side of the sensor toward the filling medium is adapted to the wavelength of ultrasound (multiples of ~/4, preferably ~/2) is used as the basic component of such sensors. The component unit 50 contains transit time counter oscillators, which to detect the sound transit times produce predetermined counting pulses at a fixed rhythm; the frequency of the ultrasound pulses transmitted by the sound pulse transmitters S1-S3 is preferably in a ratio of 1:3 to 1:6 to the frequency of the transit time counter oscillator. For the sake of high basic measurement accuracy, the resonant and operating ~requency is set to 2 MHz, which in water is equivalent to a s wavelength of 0.75 mm. The transit time counter oscillator preferably has an operating frequancy of 8 MHz.
For the temperature sensors 14-16, a differential measure-ment accuracy of approximately one-tenth of a degree is provided, so that even relatively small temperature gradi-ents within the tank 20 can be detected.
A method for determining the fill level in containers filled with fluid, preferably in tanks of tank installations, is achieved with the fill level measuring device explained above in conjunction with Figs. 1-6. In this method, the fill level height is from the sound transit time of ultrasound pulses that are projected along a main measuring path 8, extending from the bottom region of the container 20 up to the surface 9 of the fluid, by first sound pulse ``transmitters Sl and reflected from the surface g of the fluid to first sound pulse receivers (likewise S1, because transmit-receive test heads are used).
A temperature-corrected sound velocity v(T) - see component 55 of Fig. 6 - in the fluid volume is ascertained in accor-dance with the following equation:
v(T) = V (TRef) [1 ~ k ]
. .
~, :
, ..
;
~: .
2~ s From this, a temperature-corrected fill level height h~T) =
v(T) t~ is ascertained, in which the correction factor Kk is defined as described above. To ascertain the correction factor Kk, the reference path 11, with which the values vtTl) ~ v(To), Tl, To and the reference temperature TRef are measured, is used, as also already explained. From the mean temperature TM found by averaging, ~T = TM - T Ref can then be ascertained, and the temperature difference ~T can be ascertained from the difference Tl - To~ The components 49 and 55 are used to ascertain the derived variables.
In ascertaining the fill level height h(T), the sump height b in the container or tank 20 is preferably used as well.
The fill level height h (T) that takes the sump height b into account is ascertained by the following squation:
h (T) - tH v(T) + ts v(T) - a + b.
This equation and the variables it contains have already been explained previously above.
When the method is carried out, the sound pulses picked up by the sound pulse receivers Sl, S2, S3 are suitably ampli-fied as a function of the sound transit time. This opera-tion is performed in the component 51 (Fig. 6). The ultrasound reception signals are then digitized in the next stage 52, before they are carried to the evaluation , ~ -30-.
component 55 of the microprocessor. In this evaluation unit 55, the fluid volume can also be determined, on the basis of the ascertained fill level height h(T), or preferably h (T), by multiplication by a factor taken from a tank characteris-tic curve (not shown), and from that, by multiplication with the density derived from the temperature distribution, the fluid quantity can be determined. The pulse duration of the sound pulses is selected suitably to be less at low fill heights than at fill heights near a maximum allowable fill height, as already explained. When the method is carried out, the measuring tube 24 has an advantageous effect in the sense that feedback from surface motions of the fluid 10 on the fill level in the first sound waveguide 4 can be mini-mized by this waveguide itself and by multiple measurements.
Fiy. 7 also serves to illustrate an advantageous use. In this drawing, which is simplified compared with Fig. 1, measuring screens or reference reflectors 17, 18, distribut-ed over the fill level height, are installed on the inside circumference of the first sound waveguide 4. The measuring tube shown here, and identified as a whole by reference numeral 24, and which is again a combination of the ~irst and second sound waveguides, serves to accommodate and retain one or more sound pulse transmitters and receivers Sl, S2, S3 and the reference reflectors 17 and 18 of a fill level measuring device, in which the reference reflectors are disposed over the fill level height at a defined spacing from one another and from the sound pulse transmitters and receivers S1; the ultrasound pulses reflected by the refer-ence reflectors 17, 18 produce transit time differences, which together with the associated, known sound travel distances, enable the ascertainment of an average sound velocity that talces the density in the fluid volume 10 into account. From the average sound velocity and from the transit time difference, referred to the fluid surface, of the applicable ultrasound measurement beams, the fill level height can be ascertained.
,
Claims (22)
Claims:
1. A fill level measuring device for containers, which are filled with fluid, preferably for tanks of tank installations, with determination of the fill level height from the sound transit time of ultrasound pulses, which are emitted along a main measuring path, extending from the bottom region of the container to the surface of the fluid, by first sound pulse transmitters and are reflected from the surface of the fluid to first sound pulse receivers, having the further characteristics, - that means for detecting the temperature distribution over the fill level height (h) are provided, the output variable of which is a mean temperature (TM) in the fluid volume;
- that in the fluid volume, in addition to the main measuring path, a reference path is provided, including at least one second sound pulse transmitter and one second sound pulse receiver at the beginning and end of the reference path, respectively, wherein at least one reference temperature sensor is provided for measuring a reference temperature TRef the partial fluid volume of the reference path, and by means of the reference path, the sound velocity v*(TRef) in the fluid volume at the reference temperature TRef can be ascertained on the basis of a given measured transit time difference .DELTA. t*;
- so that a temperature-corrected sound velocity v(T) in the fluid volume:
v (T) = v*(TRef) [1+Kk? .DELTA. T1]
and thus a temperature-corrected fill level height h (T) = v (T) ? tH
result, in which .DELTA.T = TM - TRef .DELTA.T* = T1 -T0 and T1, T0 are two different temperatures of the fluid, measured on the reference path with a reference temperature sensor and v(T1), v(T0) are the associated sound velocities measured with the reference path, and Kk is a correction factor that on the basis of the measurements of T1, T0, v(T1), v(T0) indicates the standardized variation in the sound velocity per degree of temperature variation of the fluid volume, and wherein further tH
is the portion of the transit time difference .DELTA. t1 corresponding to the fill level height, which difference is measured with each of the first sound pulse transmitters and receivers (S1).
- that in the fluid volume, in addition to the main measuring path, a reference path is provided, including at least one second sound pulse transmitter and one second sound pulse receiver at the beginning and end of the reference path, respectively, wherein at least one reference temperature sensor is provided for measuring a reference temperature TRef the partial fluid volume of the reference path, and by means of the reference path, the sound velocity v*(TRef) in the fluid volume at the reference temperature TRef can be ascertained on the basis of a given measured transit time difference .DELTA. t*;
- so that a temperature-corrected sound velocity v(T) in the fluid volume:
v (T) = v*(TRef) [1+Kk? .DELTA. T1]
and thus a temperature-corrected fill level height h (T) = v (T) ? tH
result, in which .DELTA.T = TM - TRef .DELTA.T* = T1 -T0 and T1, T0 are two different temperatures of the fluid, measured on the reference path with a reference temperature sensor and v(T1), v(T0) are the associated sound velocities measured with the reference path, and Kk is a correction factor that on the basis of the measurements of T1, T0, v(T1), v(T0) indicates the standardized variation in the sound velocity per degree of temperature variation of the fluid volume, and wherein further tH
is the portion of the transit time difference .DELTA. t1 corresponding to the fill level height, which difference is measured with each of the first sound pulse transmitters and receivers (S1).
2. The fill level measuring device of claim 1, characterized in that the means for detecting the temperature distribution include temperature sensors which are disposed on a plurality of measurement points distributed over the fill level height, and from the temperature measured values of which the mean temperature (TM) of the fluid volume can be derived by averaging.
3. The fill level measuring device of claim 2, characterized in that the means for detecting the temperature distribution include at least one temperature sensor each disposed in the vicinity of the bottom (14), at approximately one-third (15) and at approximately two-thirds (16) of the maximum fill level height of the container.
4. The fill level measuring device of one of claims 1-3, characterized by a vertically aligned first sound waveguide (4) for the main measuring path (8), which extends from the bottom region of the container up to a height that is located above the highest fill heighth; that the interior of the first sound waveguide communicates with the remaining fuel volume of the container via openings (6); and that a first sound pulse transmitter for transmitting an ultrasound beam in the direction of the surface of the fluid volume and a first sound pulse receiver for receiving the ultrasound beam reflected from the surface are disposed on the lower end of the first sound waveguide (4).
5. The fill level measuring device of one of claims 2-4, characterized in that the temperature sensors are secured to the outside of the first sound waveguide.
6. The fill level measuring device of one of claims 1-5, characterized in that the reference path is assigned its own second sound waveguide (5), on which both the second sound pulse transmitter and receiver and the at least one reference temperature sensor are secured, and the interior of which communicates with the remaining fluid volume via at least one opening.
7. The fill level measuring device of claim 6, characterized in that the second sound waveguide for the reference path is embodied as a transverse tube disposed near the bottom of the container.
8. The fill level measuring device of claim 7, characterized in that the first sound waveguide for the main measuring path is structurally united at its lower end with the transverse tube for the reference path to make a T-shaped, continuously hollow measuring tube.
9. The fill level measuring device of claim 8, characterized in that a transmit-receive test head for the first sound pulse transmitter and receiver is secured to the inner circumference of the transverse tube wall in alignment with the longitudinal axis of the main measuring path, the test head transmitting ultrasound beams from bottom to top and receiving the ultrasound beams, oriented from top to bottom, reflected by the surface of the fluid.
10. The fill level measuring device of claim 8 or 9, characterized in that to determine the level (13) of a sump, formed by foreign fluids and contamination, below the fluid (10) in the container, a third sound pulse transmitter and a third sound pulse receiver (S3) are provided, which transmit from top to bottom and measure from bottom to top, respectively.
11. The fill level measuring device of claim 10, characterized in that the transverse tube has a downwardly pointing sound hole on one end, and a transmit-receive test head for the third sound pulse transmitter and receiver is secured to the inside circumference of the transverse tube in alignment with the axis of the sound hole and above the sound hole.
12. The fill level measuring device of one of claims 1-11, having an access pipe or dome with a lid flange and a dome lid, by means of which a fill tube for the fluid, protruding into the container interior, is guided sealingly and retained, characterized in that the measuring tube or the first sound waveguide is retained on the fill tube axially parallel to the longitudinal axis thereof, and that the measurement and current supply lines of the temperature sensors and sound pulse transmitters and receivers are laid on the outside of the first sound waveguide and are ducted to the outside through a gas-tight line duct in the dome lid.
13. The fill level measuring device of one of claims 1-12, characterized in that piezoceramic sensors serve as sound pulse transmitters and as sound pulse receivers (S1, S2, S3), and that the sound transit times are each measured from the moment of the sensor short circuit until the arrival of the first amplitude of an echo.
14. The fill level measuring device of claim 13, characterized in that for detecting the sound transit times, counting pulses specified at a fixed rhythm by a transit time counter oscillator are used, and that the frequency of the transmitted ultrasound pulses is in a ratio of 1:3 to 1:6 to the frequency of the transit time counter oscillator.
15. The fill level measuring device of claim 14, characterized in that the frequency of the transmitted ultrasound pulses is 2 MHz and the frequency of the transit time counter oscillator is 8 MHz.
16. A method for determining the fill level in contains filled with fluid, preferably in tanks of tank installations, with determination of the fill level height from the sound transit time of ultrasound pulses, which are emitted along a main measuring path, extending from the bottom region of the container to the surface of the fluid, by first sound pulse transmitters and are reflected from the surface of the fluid to first sound pulse receivers, having the further characteristics, - that a temperature-corrected sound velocity v(T) in the fluid volume is ascertained in accordance with the following equation:
v(T) = v*(TRef) ? [ 1+Kk ? .DELTA.T]
and from that, a temperature-corrected fill level height h(T) = v(T) ? tH
is ascertained, wherein the correction factor Kk is defined by the following equation:
, wherein .DELTA.T* = T1 - T0 .DELTA. T = TM - TRef and wherein the following symbols have the following meanings:
TM, the mean temperature of the fluid volume derived by measuring the temperature at a plurality of measurement points distributed over the fill level height;
v*, the sound velocity, ascertained at the reference temperature TRef along a reference path of known length located in the fluid volume, this velocity being derived from the transit time differences of the ultrasound pulses that ensue between a second sound pulse transmitter and a second sound pulse receiver at the beginning and end of the reference path, respectively;
TRef, the reference temperature at the reference path at the time of the particular transit time measurement;
T1, T0, the different temperatures of the fluid, measured at the reference path;
v(T1), v(T0), the associated sound velocities ascertained with the reference path;
Kk, a medium-specific correction factor, which indicates the standardized variation in the sound velocity per degree of temperature variation of the fluid volume; and tH, the portion of the transit time difference .DELTA. t1, corresponding to the fill level height, that is measured with the first sound pulse transmitters and receivers (S1), respectively.
v(T) = v*(TRef) ? [ 1+Kk ? .DELTA.T]
and from that, a temperature-corrected fill level height h(T) = v(T) ? tH
is ascertained, wherein the correction factor Kk is defined by the following equation:
, wherein .DELTA.T* = T1 - T0 .DELTA. T = TM - TRef and wherein the following symbols have the following meanings:
TM, the mean temperature of the fluid volume derived by measuring the temperature at a plurality of measurement points distributed over the fill level height;
v*, the sound velocity, ascertained at the reference temperature TRef along a reference path of known length located in the fluid volume, this velocity being derived from the transit time differences of the ultrasound pulses that ensue between a second sound pulse transmitter and a second sound pulse receiver at the beginning and end of the reference path, respectively;
TRef, the reference temperature at the reference path at the time of the particular transit time measurement;
T1, T0, the different temperatures of the fluid, measured at the reference path;
v(T1), v(T0), the associated sound velocities ascertained with the reference path;
Kk, a medium-specific correction factor, which indicates the standardized variation in the sound velocity per degree of temperature variation of the fluid volume; and tH, the portion of the transit time difference .DELTA. t1, corresponding to the fill level height, that is measured with the first sound pulse transmitters and receivers (S1), respectively.
17. The method of claim 16, characterized in that in the ascertainment of the fill level height h(T), the sump height (b) in the container is also taken into account, and that the fill level h*(T) taking the sump height (b) into account is ascertained in accordance with the following equation:
h*(T) = tH ? v(T) + tS ? v(T) - a + b, wherein the following symbols have the following meanings:
ts, the portion of the transit time difference .DELTA. ts corresponding to the sump height, which is measured with a third sound pulse transmitter and receiver (S3), which is disposed in the region near the bottom of the fluid volume;
a, the distance, measured vertically between the first and third sound pulse transmitters and receivers (S1-S3), and b, the sump height measured by the third sound pulse transmitters and receivers (S3).
h*(T) = tH ? v(T) + tS ? v(T) - a + b, wherein the following symbols have the following meanings:
ts, the portion of the transit time difference .DELTA. ts corresponding to the sump height, which is measured with a third sound pulse transmitter and receiver (S3), which is disposed in the region near the bottom of the fluid volume;
a, the distance, measured vertically between the first and third sound pulse transmitters and receivers (S1-S3), and b, the sump height measured by the third sound pulse transmitters and receivers (S3).
18. The method of claim 16 or 17, characterized in that the sound pulses picked up by the sound pulse receivers (S1, S2, S3) are amplified as a function of the sound transit time.
19. The method of one of claims 16-18, characterized in that the fluid volume is determined from the fill height h(T), h*(T), by multiplication by a factor taken for this purpose from a tank characteristic curve, and from that, by multiplication by the density derived from the temperature distribution, the fluid quantity is determined.
20. The method of one of claims 16-19, wherein the main measuring path extends inside a sound waveguide, characterized in that feedback from surface motions in the fluid upon the fill level in the sound waveguide is minimized by this waveguide itself and by means of multiple measurements.
21. The method of one of claims 16-20, characterized in that the pulse duration of the sound pulses is selected to be less at low fill heights than at fill heights near a maximum allowable fill height.
22. The use of a sound waveguide, embodied in accordance with one of claims 8 or 9, for accommodating and retaining not only one or more sound pulse transmitters and receivers but also the reference reflectors or screens of a fill level measuring device, in which the reference reflectors or screens are disposed over the fill level height at a defined spacing from one another and from the sound pulse transmitters and receivers, and the ultrasound pulses reflected from the reference reflectors or screens produce transit time differences, which together with the associated known sound travel lengths are used to ascertain an average sound velocity in the fluid volume that takes the density in the fluid volume into account, wherein the fill level height is ascertained from the average sound velocity and from the transit time differences, referred to the surface of the fluid, of the ultrasound measuring beams.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP89115488.2 | 1989-08-22 | ||
| EP89115488 | 1989-08-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2065405A1 true CA2065405A1 (en) | 1991-02-23 |
Family
ID=8201795
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2065405 Abandoned CA2065405A1 (en) | 1989-08-22 | 1990-08-22 | Measuring device and process for determining the level in fluid containers, preferably for tank installations, and use of a sound waveguide |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2065405A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112577588A (en) * | 2020-12-23 | 2021-03-30 | 中国石油大学(北京) | Sound velocity measuring device |
-
1990
- 1990-08-22 CA CA 2065405 patent/CA2065405A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112577588A (en) * | 2020-12-23 | 2021-03-30 | 中国石油大学(北京) | Sound velocity measuring device |
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