LT5420B - Electromagnetic flow measurer - Google Patents

Abstract

The invention relates to electromagnetic flow measurers and can be used for measuring of quantitative characteristics of liquid flow by the electromagnetic way. Electromagnetic flow measurer comprises measuring channel which is designed from non magnetic material pipe with inside insulation and with two electrodes, which are disposed opposite each other in walls, a current source, first and second coils which form magnetic field, which is perpendicular to a pipe axis and a line which joins centres of electrodes, a bearing screw, first and second differential amplifiers, a pulse forming circuit, a measuring coil, a processor, a memory device, an indicating device, a three pole switcher, and first integrating analogical digital converter, additional digital analogical converter and second integrating analogical digital converter.

Description

The invention relates to the measurement of the quantitative characteristics (flow size, flow volume or mass, etc.) of a fluid flow in a closed conduit.

A known electromagnetic flowmeter having a measuring channel consisting of a tube of non-magnetic material with an internal insulation, a control circuit actually located on the source of the excitation current, between the output and the common measuring point the first and second coils forming a magnetic field perpendicular to the axis of the tube resistances. Two electrodes are installed in the measurement channel walls so that the line connecting them is perpendicular to the axis of the tube and the direction of the magnetic field. The electrodes are connected to a differential amplifier input connected to an integrating analog-to-digital converter. The output of the latter is connected to a processor input connected to its output with an excitation current source input, an analog-to-digital converter control input group, and an indicating device inputs [European Patent EP 0521169, G01F 1 / 60,1993].

Such a flow meter has a disadvantage because its functional capabilities are insufficient. If, during operation of the flowmeter, it contains magnetic impurities or there is a magnetic error on the inside of the flowmeter, which can be large.

The prototype of the present invention is an electromagnetic flowmeter having a measuring channel consisting of a tube of non-magnetic material with internal insulation and wall diametrically opposed two electrodes, a current source, a first and a second coil forming a magnetic field, a first differential amplifier, a processor. , indication device, first, second, third, fourth and fifth tripoli switches, second differential amplifier, memory device, trapezoidal pulse generator, measuring coil and integrating analog-to-digital converter with a reference input connected to the first terminal of the reference resistor, information outputs to the first group of inputs to the processor, the group of control inputs connected to the first group of inputs of the processor, the second group of inputs of the processor to the indicating device furthermore, the second terminal of the first excitation coil is connected to the first terminal of the second coil, the second terminal of the second coil to the first reference resistor and the second terminal of the resistor is connected to a common point of the measuring circuit output, the second pole to the first terminal of the first excitation coil, the third pole to the third pole of the second tripole switch having the first pole connected to the first electrode and the second pole to the first input of the first differential amplifier, the second electrode connected to the first pole having a second pole connected to a second input of a first differential amplifier and a third pole connected to a first support resistor terminals, a fourth tripole switch connected to a first pole by an integrating analog-to-digital converter the measuring input, the second pole with the output of the first differential amplifier, the third pole with the output of the second differential amplifier, the fifth tripole switch connected to the first pole of the current control input, the second pole to the sixth output of the a pulse former output connected to a seventh processor second control output group output, the first to fifth tripole switch control inputs connected to, respectively, the first to fifth processor second control group outputs, and the memory device information output to a third processor output the information output group, the axis of the measuring coil is parallel to the channel axis, and the output is connected to the inputs of the second differential amplifier.

The prototype flowmeter has no means of verifying that there is magnetic sediment in the stream and that there is no layer of magnetic sediment without interrupting the metering channel or dismantling the measuring channel. As a result, it does not guarantee the reliability of the measurement results and sufficient accuracy of the measurement during long-term continuous measurement.

The object of the present invention is to extend the functionality of the electromagnetic flow meter, which enables to increase the reliability and accuracy of the measurement results by continuous continuous measurement.

This object is achieved by the present invention as follows. In an electromagnetic flowmeter having a measuring channel consisting of a tube of non-magnetic material with inner insulation and diametrically opposed two electrodes in the walls, the source of current, the first and second coils forming a magnetic field perpendicular to the axis of the tube and the line connecting the electrode centers , first and second differential amplifiers, pulse generator, measuring coil, processor, memory device, indication device, tripolis switch and first integrating analog-to-digital converter, the information outputs of which are connected to the processor first group of control inputs, the second group of information conclusions to the information output of the indication device and the third group of information conclusions to the information output of the memory device , a second output of the first excitation coil connected to a first second coil output, a second output of a second coil to a first reference impedance output, and a second output of the output impedance connected to a common point in the measuring circuit. a second pole of the switch, a digital-to-analog converter and a second integrating analog-to-digital converter optionally connected, the information output group connected to the fourth processor information output group, the control input group to the second processor control output group, the reference input to the digital analog converter output - to the first pole of the tripol switch with the second pole connected to the first terminal of the resistor and the control input to the third control terminal group of the processor a first output having a second output coupled to a pulse generator input having a current source connected to a first output of the first excitation coil, and a digital-to-analog converter connected to the information input group of a fifth processor and the output connected to a first integrating analog a first and second inputs of a digital converter support input coupled to the output of the first differential amplifier, connected to the measurement channel electrodes, and the axis of the measurement coil oriented parallel to the axes of the excitation coils.

The present invention significantly extends the functional capabilities of the device. The presence of magnetic particles in the flow of the liquid to be measured, or even the presence of partial magnetic sediment on the inner walls of the measuring channel, increases the magnetic conductivity of the magnetic flux that drives the measuring coil. Immediate information is provided on the instrument display unit and service personnel can take appropriate action.

This avoids measurement errors due to magnetic impurities or sediment. The reliability and accuracy of measurement results increase.

The block diagram of the electromagnetic flow meter is shown in the drawing.

The electromagnetic flow meter has a measuring channel 1 consisting of a tube of non-magnetic material with inner insulation and diametrically opposed two electrodes in the walls, a current source 2, the first 3 and a second 4 coils forming a magnetic field perpendicular to the tube axis and line a reference impedance 5, a first 6 and a second 7 differential amplifiers, a first 8 and a second 9 integrating analog-to-digital converters, a processor 10, an indicating device 11, a memory device 12, a measuring coil 13, a pulse generator 14, a digital-to-analog converter 15 and a tripole switch 16. The measurement channel electrodes are connected to the first and second inputs of the first differential amplifier 6, the output of which is coupled to the measurement input of the first integrating analog-to-digital converter 8, the reference input of which is combined with the second integrating analog. connected to the output of the digital-to-digital converter 9 to the output of the digital-to-analog converter 15, the information outputs to the first information group of the processor 10 and the control group to the first control group of the processor a third group of information outputs - with information outputs of the memory device 12, the output of power source 2 being connected to the first output of the first coil 3, the second output connected to the first output of the second coil 4, the second output of the second coil 4 to the first The second output 5 is connected to a common point in the measuring circuit, the axis 13 of the measuring coil is parallel to the 3 and 4 axes of the excitation coil, and the output is connected to the first and second inputs of the second differential amplifier 7 s with a second pole of the tripole switch 16 having a third pole connected to a first terminal of the resistor 5, a first input of the processor's third control terminal group, and a first pole with a second analogue to digital converter 9 measuring input connected to a fourth processor information terminal. a second group of processor control inputs, the second output of the third processor in the processor being connected to the input of a pulse generator 14, the output of which is connected to the input 2 of a current source, and the information input group of the digital analog converter is connected to the fifth group of CPU information inferences.

The electromagnetic flow meter works as follows. At the output of the pulse generator 14, a pulse sequence is formed with a pause equal to the pulse duration. The impulse followed by a pause forms one meter operation. By applying a pulse of amplitude Uo to the input of the current source 2, a maximum voltage U _{m is} formed at its output. Excitation current

RQ + R _r

U 7 grows as follows: I = -—— (1 - e ^r ). Where L _r and R _r - the excitation coils 3 and 4, respectively, the sum _r + R the inductance and the resistance. After a time interval, Jr = (4-r5) rr = (4-r5) Z / (T? O + T? R), its value equals Iff = U _m / (Ro + R). Once this value is established, the impulse takes at least as long as To. When the meter is in operation, the first and third poles of the tripolar switch 16 are connected. When the first pulse is operated after the meter is turned on, the measurement is performed only on the second analog-to-digital converter 9, which implements the dual integration method. At its input a voltage drop Ur constrained Rq. When June, we have ^ = ^ 2 ^ 0 = ^ 2ίΛ, 7? Ο / (Κο + ^, ·) · This voltage in the integrator of the converter 9 integrates for a given time duration Tq. If the time constant of the integrator is Γ2, at the end of the interval Tis, we will have a voltage U2-K2U _m Ro / (Ro + Rr) To / T2- at the output of the inverter 9. The excitation current gradually drops to zero. In the interval between pauses, a constant voltage Uę> of opposite polarity is applied to the inverter of the inverter 9. This voltage is integrated until the integrator output is zero. The duration of this integration is equal to T _x \. We will have the equationK2U _m Ro / (Ro + R _r ) To / T2 = UoT _x \ / T2. From this we can express the duration of T _xi :

KT u ^T xl =, ² Λ. Λη By filling this interval with a constant frequency pulse fo we obtain the number of Uq \ + R _r / RQ N _xi = T _xl f ₀ = ^K2T ° ^fo —- = K _s —— h xl xuo _Uq 1 + R _r / R _o * l + R _r / R ₀ const.

This number is input via the information outputs of the converter 9 to the processor 10, transmitted to the memory device 12 and then fed through the processor to the information inputs of the digital-to-analog converter 15. We have a voltage at the output of converter 15

U:

+ R _r / Rq

Here, K _A = const - factor.

Before supplying the second pulse to the current source 2, the first and second poles are connected at the tripolar switch 16. In the second integrating analog-to-digital converter 9, the voltage Ud2 acting at the output of the second differential amplifier 7 is integrated throughout the operation of the pulse formed by the pulse generator. Evaluating the expression of the excitation current Iz, the voltage U m. can be expressed as follows:

{R ^ + Rfjt (RQ + R _r ) t ^υ ΰ2 ^{= Κ} ΰ2 ^ Γ- ^{= Κ} ΰ2 ^Ν Μ ^ Μ ^ Γ- ^{= Κ} Ο2 ^Ν Μ ^ Μ ^ - ^{β Lr} = ^K M ^ M ^ ^{! Le Lr} ot dt L _r L _r

Here, Kd2 ~ is the gain of the second differential amplifier, Nm is the number of turns of the measuring coil, Ψμ is the total magnetic flux driving the measuring coil, 7.m is the magnetic conductivity of the flow Ψμ, Km ^ KdiNm- Pulse generator 15 pulse duration ie, »rr = Z / (Ro + ^ r) so it will have a voltage at the output of the C // converter 9 integrator at the end of it

Č7 _Z =

Κ _Μ λ

Μ ^Λ Μ inU _D2 dt =

U, (le ^Tr ) At the beginning of the pause ^r 2 o ^ 2 + i2 Rq + R _k, a second analog-to-digital converter integrator is connected to the digital-to-analog converter output voltage Ua which is the opposite of Ud2- It is integrated until zero. It takes T _X 2. Its duration will be obtained from the equation U r = ^ 4 ^ x21 _ ^ nfx2 _...... The law of this equation Ui expression, r ₂ r ₂ l + 7? _r / 7? o K * K can we express Τ _χ ϊ. T _x2 = -—— λ _Μ = Κ ₂ λ _Μ . Here K ₂ = f ¹ _n = const. Filling _a x k k R? _A x R ₀ this range fo frequency pulse, we get the expression digital proportional magnetic conductivity JmVeikiant second pulse starts at the first measurement integruojančiame analog digital converter. The voltage acting on its input begins to integrate with the stabilized value of the excitation current I _ž o- When the liquid flows, the electrodes of the measuring channel 1 produce a voltage Ue proportional to the average velocity v _{v of} the channel cross section and the magnetic flux density B. In turn, the magnetic flux density is proportional to the value of the excitation current I _ž o: B = klfo (k = const). The amplified signal in the first differential amplifier can be expressed as: Uni = XDi / zoVv = & m [i / _m / (7? O + J? / -)] vv (& ni = const). This voltage at inverter 8 integrator

Ί integrates a set time duration To. At the output of the inverter 8 integrator, if the integrator time constant is η, a voltage Ui = K _Di [U „j (Ro + R _r )] v _v To / z \ is obtained. At the onset of a pause, the polarity of the inverter 8 is connected to the opposite polarity

U ...

voltage U = K _A K _S -—- operating at the output of the digital to analog converter. The Si + R _r / Rq voltage is integrated until the integrator output is zero. The duration of this integration is T _v . We will have the equation K _D \ [U _m / (Ro + R. _{ ')] V _v To / T \ = KAK _s (U _m / (Ro + R _r )] RoT _v / xi. the voltage integration time is proportional to the average fluid flow rate and is independent of the variation of the excitation current circuit parameters: T _v = Kov _v (Ko ^ oiTo / KAKsRo-const) Filling the time interval T _{v with a} constant frequency fo pulse gives N N = Tfo = Kqfov _v , which is the output size of the converter 8. Such a change, starting with the second, is carried out further in each measuring cycle, _{and the} values of N _v obtained in each clock are stored in the memory device 12 and processed in the processor together with the values obtained in the previous cycles. Quantitative characteristics of the fluid flow of interest: instantaneous or average values of the fluid flow over time, volume or mass of liquid passed, etc.

The tripolis switch is toggled at the start of each cycle, so that the non-paired stroke in the second analog-to-digital converter 9 measures the voltage acting on the reference screw 5. Thus, the voltage at the output of the digital-to-analog converter 15 is constantly updated and changing as voltage U _s or impedance R _r . In a pair of strokes, the voltage applied to the measuring coil is measured. Thus, the numerical value of the magnetic conductivity λ _{Μ of} N _{x2 is} constantly controlled. In the processor, it is compared to the value N _{x 2} o obtained during meter calibration. Magnetic impurities in the stream or sediment on the walls of the channel in the core area increase the magnetic conductivity and cause a change Δ _χ2 = Ν _χ2 -Ν _χ2 ο. When such a change occurs, the processor generates a warning signal and outputs it to the indicating device.

The present invention makes it possible to determine very quickly the moment when magnetic impurities or sediments occur, without interrupting the measurement. This can lead to an unacceptable increase in meter measurement errors. This greatly expands the device's functionality by alerting service personnel in a timely manner about imminent decreases in measurement accuracy. It is thus possible to take timely action to reduce the accuracy of the measurement. All this increases the accuracy of the measurement and the reliability of the measurement results. Since such meters are most commonly used for commercial settlement, this is very relevant. In the meantime, cleaning the appliance before the time has passed is expensive enough, and since cleaning over a period of time interrupts the measurement, it is undesirable.

Claims (1)

DEFINITION OF INVENTION Electromagnetic flowmeter with a measuring channel consisting of a non-magnetic tube with an inner insulation and diametrically opposed two electrodes in the walls, current source, first and second coils forming a magnetic field perpendicular to the axis of the tube and the line connecting the centers of the electrodes , first and second differential amplifiers, pulse generator, measuring coil, processor, memory device, indication device, tripol switch and first integrating analog-to-digital converter, the information outputs of which are connected to the processor first group of information outputs, an inference group having a second inference for the indication device and a third inference for the memory device in addition, a second output of the first excitation coil connected to a first second coil output, a second second coil output to a first reference resistor output, and a second resistance input to a common point of the measuring circuit connecting the output of the measurement coil to the second differential amplifier inputs a second pole, further comprising a digital-to-analog converter and a second integrating analog-to-digital converter, the information output group connected to the fourth processor information output group, the control input group to the second processor control output group, the measurement input to the first tripol switch pole, and with a reference input, together with the reference input of the first integrating analog-to-digital converter, to the output of the digital-to-analog converter, a group of information inputs connects further, with the fifth processor information output group, the second pole of the tripole switch is connected to the first terminal of the resistor and the control input to the first terminal of the third control group of the processor, the second terminal connected to the pulse generator input with a current source the first inputs, furthermore, the measuring input of the first integrating analog-to-digital converter is connected to the output of the first differential amplifier, the first and second inputs are connected to the measuring channel electrodes, and the axis of the measuring coil is oriented parallel to the axes of the excitation coils.