DE2633859A1 - Electronic flowmeter transducer using comparison gas volume - converts pressure into oscillations of wire which are measured and counted - Google Patents

Abstract

The electronic flowmeter transducer operates on the comparison gas principle. Comparison gas volume is closed by a suitable diaphragm (11) and converted through a spring (14) in tension of an oscillating wire (15) stretched in a transversal magnetic field. Period of its transversal mechanical fundamental oscillation is electronically measured. A correspondingly programmed nonlinear frequency digital convertor determines from flowmeter signals the total volume in the form of a bit pattern, and applies it on appearance of a conversion signal showing the conversion end, to an electronic adder (27) and an interconnected standard volume counter (29) for recording the overflows.

Description

Electronic state volume conversion he

according to the reference gas principle is the subject of this patent application a device that measures the volume of real gases in the operating state via the volume of the room a reference gas quantity converted to the standard condition.

A transmitter with a frequency output records the volume of the reference gas volume. A corresponding electronic signal is determined from the period of oscillation of the output signal Arrangement of the state number for the gas to be converted and leads them in each case according to the Registration of an operating volume unit to the standard volume counter.

Consumption measurements are made according to the mass of the gas supplied or billed according to the volume based on the normal state. The gas mass can Determine the standard volume via the volume corrector using the operating density transmitter.

Operating density transmitters are not suitable because the signal is too small for measurements in low pressure networks. These networks form the area of application of the volume corrector, which is the respective volume ratio of the standard state for a certain gas composition for the operating status, determine the status number Z V0. In connection with an operating volume counter The standard volume can thus be measured with the usual design.

Technically, the state number can be determined with the help of a reference gas or using a suitable approximation of the real gas equation with measuring arrangements can be determined for the operating pressure and temperature.

With the reference gas principle, the volume is equal to the one to be converted Gas of the same composition in pressure and temperature equilibrium are defined closed gas quantity is the primary measurand. The reciprocal of this volume, a Measure for the sought condition number, is in reference gas devices with a mechanical Calculating gear formed.

The conversion using the real gas equation takes place according to the relationship Z (p, T) = ########## The analytical representation ties in here the law for ideal gases. The Compressibility factor k (p,), which describes deviations from the behavior of ideal gases, approximately either viewed as constant or through defined non-linearities taken into account when determining the state variables p and T. If you put these sizes with the help of suitable measuring arrangements in mechanical deflections, then can tap their quotient as the output variable of a mechanical calculating gear.

In both conversion processes, the controls exactly or approximately determined state number a continuously adjustable gear, which the revolutions of the operating volume counter is transmitted proportionally to Z to the standard volume counter.

State-of-the-art volume corrector with comparison gases as well as devices for simulating the real gas equation require a high precision engineering effort. The large number of mechanically moving parts are subject to wear and tear, which can result in long-term changes in the measurement properties.

According to the invention in the electronic volume corrector according to the reference gas principle, the volume of the reference gas quantity of a suitable Diaphragm detected and a spring element in the tensile load of an oscillating wire implemented, from its period of oscillation a correspondingly programmed non-linear Frequency-digital converter according to P 24 21 816.4 in time with the flow meter signals the status number is determined digitally in the form of a bit pattern and an electronic one Adding unit with connected roller counter for registering the overflows.

When recording the reference gas volume, a diaphragm can be used with a relatively small stroke.

On the basis of detunable mechanical oscillators working Transmitters are characterized by their simple structure and high long-term stability. The possibility of a direct digital signal processing makes every readjustment of the electronic assemblies superfluous.

In the analytical relationship between period of oscillation and state number is capable of the non-linear frequency-to-digital converter individual Variations in the oscillating wire transmitter must be included. Mechanical Aids and measures to adjust the period of oscillation can therefore omitted.

When using a suitable type of semiconductor in the electronic A battery supply is possible for each module for one measuring period. In order to the corrector can be installed independently of a mains supply.

By choosing suitable switches and an appropriate structure the explosion protection regulations can be taken into account.

Fig. 1 shows an example of the basic arrangement of vibrating wire transmitters and downstream electronics. The thinly framed circuits can be useful be arranged on a common printed circuit board.

The metal bellows fixed in the base (10) and acting as a diaphragm (11) is closed with the freely movable cap (12) and contains the reference gas quantity. It is immersed in the gas to be converted, so that when it is negligible elastic Restoring forces of the diaphragm and spring element in its free interior operating pressure and set the temperature of the gas to be converted. The cylindrical approach of (10) defines the minimum volume, the sleeve (13) the maximum volume of the Reference gas solid. At the same time, (13) provides mechanical protection for the metal bellows guaranteed.

The respective deflection of (12) is determined via the spring element (14) converted into a tensile load on the vibrating wire (15). This wire runs through the perforated stones (16) and (17), which define the vibration nodes, for insulating electrical feedthrough (18).

Transverse mechanical vibrations of (15) in the field of the permanent magnet (19) induce an alternating voltage in the oscillating wire, which makes the electronic measurement the period of oscillation makes possible.

If the vibrating wire is made of a material of density 9 and has the cross section q, then with the node spacing L and a tensile load from the force P, the oscillation period of transverse mechanical fundamental oscillations is The effective cross section of the metal bellows (11) loading the vibrating wire over the spring element (14) is F; if x is the deflection of the cap (12) compared to the cylindrical extension of (10), then the following applies to the reference gas volume V (x) = Vmin + xF Vmin is the minimum volume of the reference gas.

With this deflection, the spring element exerts the tensile load P (x) = D (x - xO) on the vibrating wire. D is the spring constant of (14), xO that position of the cap (12) at which (14) is free of forces. The associated period of oscillation thus results in If the spring constants of the spring element and metal bellows can be neglected, then the following applies to the state number V0 ~~~~~~~ Z (x) = V (x) = VminW + xF If this requirement is not met, the deflection of (12) to be based on the real gas equation (see design example).

Since the vibrating wire moves in the reference gas, it comes across a Entrainment of the gas surrounding the wire for a small effective increase the wire mass per unit length.

This effect is in the per mille range and can be just as much as the Frequency change due to the damping of movement in the von verterprogramming consider.

In a manner known per se, by means of feedback via a two-pole Oscillator circuit in phase with the signals induced in (15) a current be impressed, which undamped the vibrations of the wire. With battery operation of the corrector, however, is a one-time impetus in the interest of saving energy of the vibrating wire and a registration of the damped free vibrations.

The one-time impulse from a current pulse is transmitted via the rotary magnet (20) and reed switch (21) triggered by the flow meter univibrator (22), which controls the driver (23) provided for pulse matching. In parallel with this the univibrator signal reaches the gate (24) and the non-linear frequency Digital converter (25). The converter and the gate are made ready for operation by this signal locked for the duration of the signal.

With an appropriately selected rise time of the driver, the The start impulse of the vibrating wire did not reach the converter.

After the door has been opened again, the attenuated AC voltage signals reach via the amplifier (26) the converter, which it according to its programming processed to the state number as a function of the period of oscillation.

The end of the conversion process is signaled by the voltage level (1), the adder (27) and display (28) for accepting the suitably coded result (2) caused. Each time the highest level of the adder overflows the standard volume counter (29r) via the electromagnetically activated clutch (30) for an advance of one unit of the lowest level with the flow counter tied together. The decoupling takes place automatically by mechanical means. The load the battery is lower in this mode of operation than when using a Pulse counter for displaying the standard volume.

The display (28), a light-emitting diode or liquid crystal system, shows the last determined condition number. The supply line is used to save energy of the control signal (1) is normally interrupted by the reed switch (31). It can be closed by a push-button operated magnet (not shown) if a reading is desired.

With every signal processing, the converter monitors whether the period of oscillation of (15) is within the intended measuring range. If it is exceeded or not reached, a corresponding signal appears (3). However, it can save on an out of range also indicate a malfunction of the corrector. The display shows the flip-flops signal is set, the corresponding indicator lights when (31) is pressed light up. The monitoring arrangement is constructed in such a way that this query put the flip-flops into their idle state. This can be used to check whether the range is exceeded or faults are still pending or recur. As with mechanical correctors If the range is exceeded, the range limits Zmax / Zmin for based on the counter progress.

For ongoing monitoring, the roller counter (32) accumulates the operating volume registered by the flow meter.

If the battery (33) is removed or reinserted, the reed switch is used (34) open. This means that no sparks can form at the contact points of the battery poles form. The switch is operated by a swivel magnet in the cap of the Battery housing is only actuated when the poles have secure contact.

If no semiconductor components are used that change their switching state To be able to maintain it over shorter supply failures, a suitable dimensioned capacitor during a battery replacement the supply of the Ensure electronics. It can be expediently designed so that, in addition, at least clutch actuation is possible.

In the following design example, the relatively methane-rich Löningen-Menslage-Erdgas the systematic measurement errors of the quantity evaluator determined as a function of the state variables.

Operating pressure and temperature should be within the ranges p = 3 - 6 ata o = 0 - 30 ° C. With the compressibility numbers k (p,) available for this natural gas in tabular form, the state numbers Z (p,?) Listed in Tab. 1 result. 000 1000 200C 3000 p = 3 ata 2.920811 2.814967 2.716622 2.625164 4 ata 3.905806 3.762930 3.630545 3.507255 5 ata 4.896581 4.715777 4.548709 4.393122 6 ata 5.893187 5.673544 5.471142 5.282655 Tab. 1 A bronze metal bellows with the following data is selected as the diaphragm (11): Inner bellows diameter 33 mm, axial springing +0.7 mm / W.

Bellows outer diameter 50 mm, axial spring constant 2 kp / mmW.

Wavelength 4mm effective. Bellows cross-section 13.1 cm2 wave number 1 - calculation pressure 3 atü 2 With a rake pressure of 3 atü there are no special protective measures for ventilation of the gas line is required.

A compression-loaded St helical spring is used as the spring element (14) with the following data use: outer diameter 5.8 mm number of turns 8 wire diameter 0.7 mm spring constant 0.1576 kp / mm St-shear module 8200 kp / mm2 For the 0.2 mm # - Spring steel vibrating wire (15) is defined as the node distance L = 57mm.

Suitable fixtures in the interior of the metal bellows can be used achieve minimum reference gas volume of Vmin = 2,213 cm3; the cap (12) lies here on the cylindrical extension of (10). A gas filling with V0 = 12,825 Norm-cm3 Löningen-Menslage-Gas results in this position as the equilibrium position for p = 6 ata # = 0 ° C At 0.71 mm preload of the spring element, the associated Period of oscillation of (15) tmax = 1,709 msec.

A deflection of the metal bellows by A = 1,897 mm results in the maximum Reference gas volume Vmax = 4,698 cm3 and the equilibrium position for p = 3 ata 4 = = 30 ° C The associated period of oscillation is now tmin = 0.892 msec, so that t is almost covers an octave.

Because of the elastic reaction of the metal bellows and spring element the number of states can only be reproduced exactly at an average gas temperature #. With # = 18 ° C, the following relationships between t2, p and Z can be derived: 10.770331 0.2361337 P = 2.0668902 + 1 - t2 + 0.1776444 t2 1 Z = 1.1042379 - 0.00256 p These relationships were used as the basis for the compilation of Table 2.

Tab. 2 contains a programming example for the non-linear frequency digital -Converter for digital determination of the State number Z. The state number is here as the result of a through the period of oscillation t or an integer Multiple kt limited addition process with section-wise constants from one programmable read-only memory received summands.

If k = 5 periods of oscillation are used as the time base, then corresponds to with a 2MHz addition clock, the time span tmin to 1.9184tmin, which covers the entire Oscillation duration range covered, 32 linear sections with 256 addition steps each. After every 256 steps, the addressing switches to the next storage group in the read-only memory and the slope of the linear approximation can change.

The adder consists of 8 binary levels for the summands from the Read-only memory and 4 downstream BCD levels, the overflow of the most valuable Binary stage are fed. The three-digit display is the one with the lowest value BOD stage not connected.

Column 1 of Table 2 contains the points tv / tmin on a relative time scale, where the addressing of the read-only memory continues. In column 2 are the values Z, Z (t,), which are exactly valid for the operating temperature 6 = 18 ° G and take into account the elastic repercussions of the metal bellows and the spring body. split 3 contains the rounding of Z to four decimal places.

These values (Z are in the BCD levels after 256 addition cycles with constant summands. Column 4 gives the differences t (Z> again; from this the binary contents of the read-only memory listed in column 5 can be viewed directly derive.

Finally, column 6 contains the relative errors ## = (Z #) - Z # Z # the state numbers for the 32 joints of the linear approximation; they lay between +0.16 # and -0.13% o.

With this programming, the initial value and base value of the non-linear frequency-digital converter (see P 24 21 816.4) are A = -8920, o = -10001011011000, B = 2.621, o = 0010.0110 0010 O001XCD Tab. 3 shows for the selected operating pressures and -temperature the simulation of the state numbers by the corrector. 1 2 3 4 5 6 0 1.0000 2.620589 2.621 - - +0.16 1 1.0287 2.749285 2.749 0.128 10000000 -0.10 2 1.0574 2.876361 2.876 0.127 01 111 111 -0.13 3 1.0861 3.001813 3.002 0.126 01111110 +0.06 4 1.1148 3.125637 3.126 0.124 01111 100 +0.12 5 1.1435 3.247816 3.248 0.122 01111010 +0.06 6 1.1722 3.368337 3.368 0.120 01 111 000 -0.10 7 1.2009 3.487180 3.487 0.119 01 110 111 -0.05 8 1.2296 3.604330 3.604 0.117 01 110 101 -0.09 9 1.2583 3.719771 3.720 0.116 01110 100 +0.06 10 1.2870 3.833485 3.833 0.113 01110001 -0.13 11 1.3157 3.945461 3.945 0.112 01 110 000 -0.12 12 1.3444 4.055682 4.056 0.111 01101111 +0.08 13 1.3731 4.164142 4.164 0.108 01101100 -0.03 14 1.4018 4.270834 4.271 0.107 01101011 +0.04 15 1.4305 4.375749 4.376 0.105 01101001 +0.06 16 1.4592 4.478884 4.479 0.103 01 100 111 +0.03 17 1.4879 4.580241 4.580 0.101 01 100 101 -0.05 18 1.5166 4.679822 4.680 0.100 01 100 100 +0.04 19 1.5453 4.777629 4.778 0.098 01100010 +0.08 20 1.5740 4.873671 4.874 0.096 01 100 000 +0.07 21 1.6027 4.967954 4.968 0.094 01011110 +0.01 22 1.6314 5.060488 5.060 0.092 01011 100 -0.10 23 1.6601 5.151285 5.151 0.091 01011011 -0.06 24 1.6888 5.240362 5.240 0.089 01011001 -0.07 25 1.7175 5.327735 5.328 0.088 01011000 +0.05 26 1.7462 5.413414 5.413 0.085 01 010 101 -0.08 27 1.7749 5.497426 5.497 0.084 01 010 100 -0.08 28 1.8036 5.579784 5.580 0.083 01010011 +0.04 29 1.8323 5.660510 5.661 0.081 01010001 +0.09 30 1.8610 5.739628 5.740 0.079 01001111 +0.06 31 1.8897 5.817159 5.817 0.077 01001 101 -0.03 32 1.9184 5.893130 5.895 0.076 01001100 -0.02 Tab. 2 The relative errors are between + 1.43SÓo and -1e59% o and are essentially due to the elastic restoring forces of the metal bellows. A modified structural design can reduce this deviation. In the case of a three-digit display of (Z), there are a maximum of deviations of one unit from the lowest digit. 000 OOG 200C 300G p = 3 ata 2,925 2,817 2,716 2,621 4 ata 3,905 3,763 3,632 3,506 5 ata 4,893 4,714 4,548 4,394 6 ata 5,886 5,671 5,473 5,285 Tab. 3 The operating temperature of the gas not only affects the reference gas volume, but also influences the node spacing, mass per unit length and tensile load of the vibrating wire via the thermal expansion of the materials and the temperature-dependent shear modulus of the spring element. With a vibrating wire transmitter according to our design example, the period of oscillation changes by + 1.6% o if the operating temperature fluctuates by + 15 ° C. Becomes 3; appropriately reduced, the total error of the volume corrector thus remains below +2.3% o. With the use of suitable spring materials (Elinvar, Nivarox) the temperature contribution of the total error can be reduced.

Fig. 2 shows the connection between 5 and Z according to Tab.

2. Detail A gives, greatly enlarged and with exaggerated differences Step widths shown, the joint between two approximation sections again.

Fig. 3 is an example of the technical implementation of an oscillating wire transmitter with reference gas filling. Instead of the metal bellows, a welded diaphragm bellows system is used here (11) used; The membrane spacing is in the interest of a clear representation drawn too big. The connections to the base (10) and to the cap (12) also form Inert gas welds.

Sleeve (13) and base (10) are against each other with the help of a fine thread axially adjustable. Two radial grooves in (13) allow the use of one for this suitable adjustment tool.

With a layer of locking varnish on the thread attachment, the so adjustable maximum membrane deflection can be fixed. A series of holes along the circumference of (13) ensures sufficient flushing of the diaphragm bellows by the gas to be converted.

The spring element (14) is made of hardened and suitable tempered tool steel. In one subjected to heat treatment in this way A helical groove is ground into a hollow cylindrical blank. The result is a helical spring that can withstand pressure, which is due to the lack of Cold forming a largely hysteresis-free and long-term stable mechanical Behavior shows. One end of the spring element ends in a collar that is in a recess of the cap (12) is crimped; the other end carries a tubular Approach into which the oscillating wire (15) is soldered.

Just like in the gas-tight, insulating electrical bushing (18) the oscillating wire is also slightly off-center in the tubular extension of (14) soldered in such a way that (15) defines the position of the oscillation nodes Perforated stones (16) and (17) rests. The perforated stone (16) is in a recess of (10) crimped; the perforated stone (17) is in a corresponding manner in the one cylindrical extension of (10) pressed-in intermediate piece (35) supported. About notch effects keep away from the vibrating wire, the outer edges of the holes in (16) and (17) rounded (see detail of vibrating wire guide).

The magnet consists of the two slots in (10) transversely magnetized ferrite parts (19.1) and the return sleeve pressed onto (10) (19.2) made of soft iron. Because of the use of identical parts, the pole faces are of (19.1) is slightly convex corresponding to the inner diameter of (19.2).

The threaded pin (36) provided with a longitudinal groove presses with his polished rounded tip on the plate (37) made of pure aluminum, which is a The bore in (10) is hermetically sealed. This hole is used when the screw is loosely screwed in Refill the reference gas filling after the system has been evacuated of the transmitter in a suitably tempered and to the desired pressure adjusted reference gas atmosphere. With one in this atmosphere The protruding tool is then tightened (36) and closes the reference gas volume via (37) gastight in the diaphragm bellows. A drop of locking varnish in the longitudinal groove of (36) is brought, fixes the metal seal in this position.

Adding helium to the reference gas enables a sensitive Leak test with the help of a mass spectrometric leak detector.

The oscillating wire transmitter is shown in the installation position; at the end flange attached to the holding tube (38), it is immersed in the gas to be converted. Should the Plug connection (39) are outside the gas atmosphere, the sealing ring (40) necessary.

The transmitter does not contain any mechanical adjustment devices Influence the period of oscillation and does not require any tight manufacturing tolerances during its manufacture, since all specimen fluctuations are individually programmed of the non-linear frequency-to-digital converter can also be taken into account. This programming can be done on a fully automatic calibration stand and does not require qualified personnel.

Blank page

Claims (8)

Electronic volume corrector according to the reference gas principle, characterized in that the volume of the reference gas quantity is recorded by a suitable diaphragm (11) and converted into the tensile load of an oscillating wire (15) stretched in a transverse magnetic field via a spring element, from which it is electronically transferred the induction signals of the measured oscillation duration of transversal mechanical basic oscillations a suitably programmed non-linear frequency-to-digital converter In the cycle of the flow meter signals the state number is determined digitally in the form of a bit pattern (2) and fed to the converter signal (1) indicating the end of the conversion to an electronic adder (27) with attached mechanical standard volume counter (29) to register the overflows. 2. Electronic volume corrector based on the reference gas principle according to claim 1, characterized in that the fixed knot position of the transversal mechanical fundamental vibrations of the vibrating wire (15) through the daughter stones (16) and (17) is determined, with a defined support of the vibrating wire in the Perforated stones by a slightly eccentric wire attachment outside of the vibration range is guaranteed. 3. Electronic volume corrector based on the reference gas principle according to claim 1 and 2, characterized in that the spring element (14) consists of a hardened and suitably tempered blank made of tool steel Grinding in a helical groove is made. 4. Electronic volume corrector based on the reference gas principle according to claims 1 to 3, characterized in that for the purpose of saving energy in battery operation from the rotary magnet (20) attached to the meter shaft of the flow meter the reed switch (21) is actuated via the univibrator (22) and the driver (23) a current pulse to initiate a dampened transversal mechanical fundamental oscillation on the vibrating wire (15). 5. Electronic volume corrector based on the reference gas principle according to claim 1 to 4, characterized in that in order to save energy Battery operation of the standard volume counter (29) via the electromagnetically activated Clutch (30) each time the highest digit of the adder overflows (27) for a feed of one unit of the lowest value counter with the Flow meter is connected, the decoupling automatically on mechanical Ways takes place. 6. Electronic volume corrector based on the reference gas principle according to claims 1 to 5, characterized in that for the purpose of saving energy in battery operation the light-emitting diode or liquid crystal display (28) by a push button Magnet is controlled via the reed switch (31), if a reading of the respective last determined condition number is desired. 7. Electronic volume corrector based on the reference gas principle according to claim 1 to 6, characterized in that to avoid sparks on the contact points of the battery poles when removing or inserting a battery the one in series with the battery (33) and via a swivel magnet in the Closing cap of the battery housing actuated reed switch (34) is open when a battery is removed or inserted. 8. Electronic volume corrector based on the reference gas principle according to claim 1 to 7, characterized in that after a bore in the Base (10) filled the transmitter immersed in the reference gas atmosphere the hermetic closure of this opening by means of a pure aluminum plate that acts as a metal seal (37) takes place, which is carried out by the rounded polished tip of the in a suitable manner to be secured threaded pin (36) is pressed.