WO2016202533A1

WO2016202533A1 - Method and device for determining the filling level of a filling material in a container

Info

Publication number: WO2016202533A1
Application number: PCT/EP2016/061584
Authority: WO
Inventors: Christian Seiler; Jörg Füglistaller
Original assignee: Endress+Hauser Gmbh+Co. Kg
Priority date: 2015-06-15
Filing date: 2016-05-23
Publication date: 2016-12-22
Also published as: DE102015109480B3

Abstract

The invention relates to a method for determining the filling level (L) of a filling material (2) in a container (1) by measuring the propagation time (t) of microwave signals, and to a device suitable for carrying out this method. The method is distinguished by the fact that the transmission signal pulse (s) or the reception signal (e) is modulated, preferably by means of signal amplification or pulse width modulation. In this case, the modulation is dependent on the time difference (Δ_T) between the triggering of the transmission signal pulse (s) and the triggering of a reference signal pulse (s'). The modulation according to the invention causes the resulting signal (ZF) for determining the filling level to have an approximately constant amplitude even in the case of filling levels (L) which differ greatly from one another. This makes it possible to evaluate the resulting signal and to carry out the associated determination of the filling level (L) with a considerably reduced amount of outlay in terms of circuitry. This saves costs when producing the device.

Description

Method and device for determining the level of one in one

Container located filling

The invention relates to a method for determining the filling level of a filling material located in a container by measuring the transit time of microwave signals, as well as a device suitable for carrying out the method.

In automation technology, in particular in process automation technology, field devices are often used which serve to detect and / or influence process variables. For the detection of process variables, sensors are used, for example, in level gauges, flowmeters, pressure and pressure gauges

Temperature measuring devices, pH redox potential measuring devices, conductivity meters, etc. are integrated, which record the corresponding process variables level, flow, pressure, temperature, pH, redox potential or conductivity. to

Actuators, such as valves or valves, are used to influence process variables

Pumps through which the flow of a liquid in a pipe section or the level in a container can be changed. In principle, field devices are all devices that are used close to the process and that supply or process process-relevant information. In the context of the invention, field devices therefore also include remote I / Os, radio adapters or generally electronic ones

Understood components that are arranged at the field level. A variety of such field devices is manufactured and sold by the company Endress + Hauser.

Non-contact measuring methods have been established for measuring the filling level, since they are robust and require little maintenance. Another advantage is the ability to measure steplessly. Especially radar-based measuring methods, which are based on the transit time principle, have prevailed here. In these measuring methods, also known as pulse radar, short microwave pulses are periodically applied at a predetermined repetition rate, e.g. in the order of 1 to 2 MHz with natural frequencies in the gigahertz range in the direction of the medium. With pulse radar-based level measuring devices, such as the FMR20 series, this is done with a repetition frequency of approx. 7 MHz. Their in the direction of sending and

Receiving device back reflected signal components are then received after a dependent of the distance covered in the container travel time. In this case, an auxiliary signal is derived on the basis of the received signal regularly, that in the

Reception signal contained amplitude and phase information of the received signal as a function of the associated running time. The resulting signal, which is often referred to as an intermediate frequency signal, is generated on account of the high signal frequencies and, as a rule, very short propagation times or transit time differences to be resolved. It is a time-stretched image of the received signal. A corresponding method is described, for example, in EP 1 324 067 A2. As also described there, the resulting signal is conventionally subsequently rectified and fed via a low-pass filter and an analog-to-digital converter to an evaluation unit. Here, the duration of the microwave pulses is determined on the basis of the resulting signal. Since the amplitude of the received signals decreases with the square of the traveled distance, the received signal can have very different amplitudes. In order to be able to measure the measurement signal in spite of the strong level fluctuations, the resulting signal generally has to be standardized by a logarithmic unit.

The circuit complexity in the evaluation of the resulting signal is thereby significant. Especially the logarithmization is associated with high circuit complexity. This requires a comparatively complex circuit architecture of the evaluation circuit. Especially from a cost point of view, it is therefore desirable to be able to dispense with such a complex circuit architecture without sacrificing reliability or measuring accuracy.

The publication DE 10 2007 058 287 A1 describes a time-equivalent scanning radar whose transmission power is controlled as a function of a sampling time in order to equalize the intensity of the time-extended received signal.

Publication JP 002010281643 A shows a pulse-radar system in which the pulse width of the transmission signal is controlled as a function of the distance in order to adjust the amplification of the received signal.

A distance-dependent control of the pulse width of the transmission signal in a pulse radar-based level gauge is described in the document WO 002015000068 A1. In the publication US 020090033543 A1 is a pulse radar-based

Level gauge shown in which the pulse width of the transmission signal is set depending on a variety of parameters, such as the type and surface of the contents, tank height and other tank-specific properties. A pulse radar-based level gauge, in which the received signal in

Pending the level value is enhanced, is disclosed in the application US 020120036927 A1. The invention is therefore based on the object to propose a radar-based method for level measurement, through which a low circuit complexity of the evaluation circuit is achieved, and a suitable for this purpose

To provide device. The invention solves this problem by a method for determining the level of a filling material located in a container by measuring the duration of

Microwave signals, the method comprising the following steps:

An electrical transmission signal pulse is triggered at a first repetition frequency, the transmission signal pulse having a natural frequency suitable for generating a microwave signal,

with a second repetition frequency, an electrical reference signal pulse is triggered,

the time difference between the triggering of the transmit signal pulse and the triggering of the reference signal pulse is determined,

- The transmit signal pulse is modulated, the modulation depending on the

Time difference is,

by means of the modulated transmit signal pulse, the microwave signal is generated, an echo signal, which by reflection of the microwave signal at the

Surface of the filling material is generated, is received,

the echo signal is converted into an electrical received signal,

the received signal is sampled by the reference signal pulse such that a resulting signal is formed,

the runtime is determined by means of the resulting signal,

Based on the running time, the level is determined.

As a result of this method according to the invention, which is based on the pulse radar method according to the prior art, it is achieved that the amplitude of the resulting signal changes only to a small extent, even with strongly differing fill levels, and therefore has a smaller or shallower dynamic , This is achieved by modulation of the transmit signal pulse and allows a simplified design of the evaluation circuit, since compared to the prior art, for example, the logarithm to adapt the amplitude to the dynamic range of the other transmitter is not required. Logarithmers also have the disadvantage that noise increases significantly at very small signal amplitudes of the received signal Thus, a narrow-band pre-filtering of the signal is necessary there, which must be tuned costly in the production of each device.

In an advantageous form of the method, the received signal is additionally modulated, wherein the modulation is dependent on the time difference between the triggering of the transmission signal pulse and the triggering of the reference signal pulse. As a result, an even more precise adaptation of the amplitude can take place than if only the transmission signal pulse is modulated.

The object is further achieved by a method for determining the level of a filling material located in a container by measuring the duration of

Microwave signals, comprising the following steps:

a time difference between the triggering of the transmission signal pulse and the triggering of the reference signal pulse is determined,

by means of the transmit signal pulse, a microwave signal is generated,

an echo signal, which is generated by reflection of the microwave signal on the surface of the filling material, is received,

the echo signal is converted into an electrical received signal, the received signal is modulated, the modulation being dependent on the time difference,

the received electrical signal is sampled by the reference signal pulse such that a resulting signal is formed,

the runtime is determined by means of the resulting signal,

Based on the running time, the level is determined.

In contrast to the two aforementioned variants of the method, no modulation of the transmit signal pulse is provided in this variant.

An advantageous embodiment of all previously described method provides that for the modulation of the transmit signal pulse and / or for the modulation of the

Receiving signal, a signal amplification and / or a pulse width modulation can be used / is. Both types of modulation affect the signal power of either the transmit signal pulse or the receive signal, which can each be used to adjust the amplitude of the resulting signal. It goes without saying even that any other form of modulation can be used that can affect the signal power.

In a further development of the method described above, in the event that the modulation of the transmission signal pulse and / or of the received signal is a signal amplification, the amplification factor increases with increasing

Time difference increased. This type of control causes those received signals, which are caused by lower levels and thus have a weaker amplitude, to be amplified higher.

Alternatively, in the event that the modulation of the signal pulse and / or the received signal is a pulse width modulation, the pulse width is increased with increasing time difference. Also, this type of control has the same effect, namely a higher gain of those received signals, which have a weaker amplitude due to low levels.

According to a preferred embodiment of the method, the sampling of the

Received signal by cross-correlation performed by the reference signal pulse, wherein the reference signal pulse has the natural frequency of the transmit signal pulse.

Furthermore, the object of the invention is achieved by a device for determining the filling level of a filling material in a container, wherein the device uses at least one of the methods described above. For this purpose, the device comprises:

A signal generating unit for generating the electrical transmission

Signal pulse,

a reference signal generation unit for generating a reference electrical signal pulse,

a transmitting / receiving unit for emitting a generated by the transmission signal pulse microwave signal in the direction of the contents and

for generating an electrical reception signal caused by the receipt of an echo signal,

at least one modulation unit for modulating the electrical signal pulse and / or the received signal,

an intelligent unit for determining the time difference between trips of the

Transmit signal pulse and trigger the reference signal pulse and

for controlling the at least one modulation unit,

A sampling unit for sampling the received signal by means of the reference signal pulse, a control / evaluation unit for determining a duration based on the

Sampling resulting signal, and

for determining the fill level by means of the runtime. With this device, the invention described above

Procedures are performed. It is achieved by the device that the resulting signal has an approximately constant amplitude even at very far apart levels. As a result, in the evaluation circuit of the

Device are dispensed with a separate adjustment of the amplitude, thereby reducing the complexity of the evaluation circuit. In addition to the technical aspect, this also plays an important role from a cost engineering point of view, since in particular circuit modules for logarithmization are cost-intensive components. Thus, the inventive idea also contributes to the fact that the manufacturing costs of the device for level measurement can be reduced.

In a development of the device, the intelligent unit and the control / evaluation unit are an integral part of a common circuit unit. As a result, the space required and the energy consumption of the device are reduced with appropriate design.

It is also advantageous if the modulation unit of the device is an amplifier circuit and / or a pulse width modulator. Both types of modulation affect the signal power of the transmit signal pulse or the

Reception signal. In this way, the amplitude of the resulting signal can be adjusted so that it is approximately constant even with highly fluctuating levels.

Moreover, it is premature if the sampling unit of the device is a mixer which performs a cross-correlation of the received signal by means of the reference signal pulse.

The invention will be explained below with reference to FIG. 1. It shows:

Fig. 1: Device for determining the level of a filling material located in a container.

In Fig. 1, a device for determining the level L of a filling 1 located in a container 2 is shown. The device is based on measuring the transit time t between emitting a microwave signal S and receiving a through the Surface of the medium 2 generated echo signal E. The microwave signal S is generated by a signal generating unit 3, in which with a repetition frequency f _c, an electrical transmission signal pulse s is generated. For this purpose, the signal generating unit 3 comprises a pulse generator for generating the electrical transmission signal pulses s, which have a periodicity corresponding to f _c . By the pulse generator, a high-frequency oscillator is controlled, which has a natural frequency f _H F. As a result, the periodically high-frequency electrical transmission signal pulses s are generated, wherein the length of the respective pulse is predetermined by the pulse generator. The transmission signal pulse s is fed to a transmission / reception unit 5. This is constructed in two parts in the illustrated embodiment and consists of a

Directional coupler and an antenna. The antenna is designed as a horn antenna and generates accordingly a freely radiating microwave signal S. According to the invention, however, it can just as well be a guided radar. In the illustrated embodiment, the horn antenna also receives the echo signal E and converts it into an electrical reception signal e. Alternatively, this can also be done by a separate receiving antenna.

The core of the invention, as shown in Fig. 1, is that either the transmission signal pulse s or the received signal e, or both are modulated by a respective modulating unit 6. In Fig. 1 it is stated that both the transmit signal pulse s and the received signal e are modulated. In the case of the modulation, the representation shown is a signal amplification with a gain factor a. The magnitude of the amplification factor a is dependent on the time difference Δτ between the triggering of the transmission signal pulse s and the triggering of a reference signal pulse s'. The time difference Δτ is detected by the intelligent unit 7 in the exemplary embodiment shown. The intelligent unit 7 simultaneously controls the amplification factor a. The control is designed such that the amplification factor a of the

Signal gain is increased to greater time differences Δτ out. Because of the

Time difference Δτ is also dependent on which received signals e are further processed by the sampling to form a resulting signal ZF. With very small time differences Δτ, those received signals e are not suppressed by the sampling, which results from near distance, ie high fill levels L. In parallel, those receiving signals e are not suppressed by the sampling at large time differences .DELTA.τ, which are reflected back from further distance, ie low levels L back.

In order to realize this type of sampling, it is necessary to provide a sampling signal s' for sampling the received signal e. The sample signal s' must in this case have a second repetition frequency f _c , slightly from the first

Repeat frequency f _{c of} the transmission signal pulse s and the received signal e deviates. In principle, the signal form of the sampling pulse s' is not predetermined. For example, the scanning signal s may be a Dirac pulse, which is generated at a reference frequency f _c . However, in order to realize a cross-correlation, ie an advantageous form of sampling, the sampling signal s must have the same characteristic as that of the transmission signal pulse s. For this reason, a reference signal generating unit 4 generates a reference signal pulse s' having these characteristics. Therefore, the reference signal generating unit 4, like the signal generating unit 3, has a pulse generator for generating electric power

Pulses of the periodicity f _c and a high-frequency oscillator with a natural frequency of f _HF .

The scanning is, as shown in Fig. 1, performed by a mixer 8, wherein the sampling is carried out by the mixer 8 by means of cross-correlation. By means of the cross-correlation, the resulting signal ZF is formed.

The type of control of the amplification factor a according to the invention has the consequence that those resulting signals ZF, which are generated by low fill levels L, are amplified more strongly than those resulting signals ZF, which arise at high fill levels. As a result, all resulting signals ZF, regardless of whether resulting from low or high levels L, an approximately equal amplitude. It is thus the weaker reflection of the echo signal E at long distances, so low levels L compensated.

Due to the very constant amplitude of the resulting signal ZF it becomes

According to the invention possible to dispense with a complex evaluation circuit. The resulting signal ZF can thereby be evaluated without expensive filtering or logarithmization. On the basis of the resulting signal ZF, which according to the invention has a very homogeneous amplitude, the fill level L is determined. This is done in the representation shown in Fig. 1 by the control / evaluation unit. 9 LIST OF REFERENCE NUMBERS

1 container

2 contents

3 signal generation unit

4 reference signal generation unit

5 transceiver unit

6 modulation unit

7 Smart unit

8 sampling unit

9 control / evaluation unit

a gain factor

E echo signal

e received signal

fc First repetition rate

fc Second repetition frequency

f (HF natural frequency

L level

S microwave signal

s transmit signal pulse

s' reference signal pulse

t term

Δτ time difference

IF Resulting signal

Claims

claims

1. A method for determining the filling level (L) of a filling material (2) located in a container (1) by measuring the transit time (t) of microwave signals, comprising the following method steps:

With an initial repetition frequency (f _c ), an electrical transmission signal pulse (s) is triggered, the transmission signal pulse (s) having a natural frequency (f _HF ) suitable for generating a microwave signal (S),

with a second repetition frequency (f _c ), an electrical reference signal pulse (s) is triggered,

the time difference (Δτ) between triggering the transmit signal pulse (s) and

Triggering of the reference signal pulse (s) is determined

the transmit signal pulse (s) is modulated, the modulation being dependent on the time difference (Δτ),

by means of the modulated transmit signal pulse (s), the microwave signal (S) is generated,

an echo signal (E), which is generated by reflection of the microwave signal (S) on the surface of the filling material (2), is received,

the echo signal (E) is converted into an electrical received signal (e), - the received signal (e) is in such a way by the reference signal pulse (s')

sensed that a resulting signal (IF) is formed,

the transit time (t) is determined by means of the resulting signal (ZF),

Based on the running time (t), the level (L) is determined.

2. The method of claim 1, wherein the received signal (e) is modulated, wherein the modulation is dependent on the time difference (Δτ).

3. Method for determining the fill level (L) of a filling material (2) located in a container (1) by measuring the transit time (t) of microwave signals, comprising the following method steps:

An electrical transmission signal pulse (s) is triggered at a first repetition frequency (f _c ), the transmission signal pulse (s) having a natural frequency (f _H F) suitable for generating a microwave signal (S).

a time difference (Δτ) between triggering the transmit signal pulse (s) and

Triggering of the reference signal pulse (s) is determined

by means of the transmission signal pulse (s), a microwave signal (S) is generated, an echo signal (E), which is generated by reflection of the microwave signal (S) on the surface of the filling material (2), is received,

the echo signal (E) is converted into an electrical received signal (e), the received signal (e) is modulated, the modulation being dependent on the time difference (Δτ),

the electrical received signal (e) is sampled by the reference signal pulse (s') such that a resulting signal (ZF) is formed,

the transit time (t) is determined by means of the resulting signal (ZF),

Based on the running time (t), the level (L) is determined.

4. The method according to at least one of the preceding claims, wherein

for the modulation of the transmission signal pulse (s) and / or for the modulation of the

Received signal (s) a signal amplification and / or a pulse width modulation is used / will.

5. The method according to at least one of the preceding claims, wherein in the event that it is in the modulation of the transmit signal pulse (s) and / or the

Receiving signal (e) is a signal gain, the gain factor (a) with increasing time difference (Δτ) is increased.

6. The method according to at least one of claims 1 to 4, wherein in the event that it is in the modulation of the transmit signal pulse (s) and / or the received signal (e) is a pulse width modulation, the pulse width with increasing time difference (Δτ ) is increased.

7. The method according to at least one of the preceding claims, wherein

the sampling of the received signal (e) is carried out by means of cross-correlation by the reference signal pulse (s'), the reference signal pulse (s) having the natural frequency (f HF).

8. A device for determining the filling level (L) of a in a container (1) located filling (2) by means of a in at least one of the preceding

Claims described methods comprising

A signal generation unit (3) for generating the electrical transmission signal pulse (s),

a reference signal generating unit (4) for generating the reference electrical signal pulse (s'), a transmitting / receiving unit (5) for emitting the generated by the transmission signal pulse (s) microwave signal (S) in the direction of the filling material (2) and

for generating the electrical reception signal (e) caused by the receipt of an echo signal (E),

at least one modulation unit (6) for modulating the transmit signal pulse (s) and / or the received signal (e),

an intelligent unit (7) for determining the time difference (Δτ) between triggering the transmission signal pulse (s) and triggering the reference signal pulse

(s') and

for controlling the at least one modulation unit (6),

A sampling unit (8) for sampling the received signal (e) by means of

Reference signal pulse (s'),

a control / evaluation unit (9) for determining a transit time (t) from the sample resulting from the sampling signal (ZF), and

for determining the filling level (L) by means of the running time (t).

9. Device according to claim 8, wherein the intelligent unit (7) and the control / evaluation unit (9) are an integral part of a common circuit unit.

10. Device according to claim 8 or 9, wherein the modulation unit (6) is an amplifier circuit and / or a pulse width modulator.

A device according to at least one of claims 8 to 10, wherein the scanning unit (8) is a mixer which detects a cross-correlation of

Receiving signal (s) by means of the reference signal pulse (s') performs.