RU1536957C - Vibration flowmeter - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: circuit 6 of vibration excitation with electromagnetic vibrator 2 sets sensitive element 2 into continuous oscillatory motion. Signals going to inputs of comparator-amplifiers 14, 15 are formed across outputs of pickups 4,5 of angular deviations. Control circuit 11 of comparator-amplifiers forms from input signal of pickup 4 logic controlling signals with difference 0/1 (1/0) at moments when input signal reaches extreme value (for instance, minimum) going to gating inputs of comparator-amplifiers 14, 15. Comparators 14, 15 switch on in succession and form sequences of pulses which do not coincide in time. Output signals of comparators 14, 15 go through precision univibrators 16, 17 to inputs of circuit 18 of extraction of time intervals. Circuit 18 controls passage of quantizing pulses of generator 19 through logic AND gates 20, 21 to summing and subtracting inputs of reversible counter 22. Output code of reversible counter is proportional to mass flow rate of controlled medium. Duration of measurement time of flow rate is set by counter-divider 12. Control over operation of flowmeter is carried out by logic control circuit 13. Increased accuracy of measurement of flow rate is achieved thanks to exclusion of errors of effect of "dead zone" and nonlinear distortions of signal while measuring phase difference of signals of pickups of angular deviations. EFFECT: enhanced accuracy of measurement of flow rate. 2 dwg

Description

 The invention relates to measuring technique and can be used in mass flow measurement systems for a wide class of process media in various industries.

 The purpose of the present invention is to improve the accuracy of flow measurement.

 In FIG. 1 is a block diagram of a vibratory flow meter; figure 2 timing diagrams of its operation in the presence of flow. The vibrating Coriolis flowmeter (Fig. 1) consists of a primary transducer 1 with a sensing element 2, on which an electromagnetic vibrator 3 and angular deviation sensors 4 and 5 are fixed. The oscillation excitation circuit 6 contains a reference voltage source 7, a peak detector 8 and a power amplifier 9 and in combination with an electromagnetic vibrator forms a tuning fork oscillation generator, the measuring transducer 10 consists of a control circuit for amplifiers-comparators 11, a counter-divider 12, a control logic 1 3, two amplifiers-comparators 14 and 15, two precision single-shots 16 and 17, a circuit for allocating time intervals 18, a quantizing pulse generator 19 of the first and second logic elements And 20 and 21, a reversible counter 22 and an output signal generating circuit 23.

 The flow meter operates as follows.

поступает на суммирующий вход реверсивного счетчика 22 (фиг.1), а с выхода элемента 21 пакет импульсов N₂=

на вычитающий вход этого счетчика. На выходе реверсивного счетчика устанавливаются показания N=N₁-N₂, пропорциональные разности длительностей импульсов 9 и 10 и, соответственно, расходу контролируемой среды через первичный преобразователь.The oscillation excitation circuit 6 (Fig. 1) with an electromagnetic vibrator 3 brings the sensing element 2 into continuous oscillatory motion. As a result, at the output of the angular deviation sensors, signals 1 and 2 are formed (Fig. 2), which are fed to the input of the measuring transducer. The output signal of the sensor of angular deviations 4 (Fig. 1) is supplied to the control circuit of the amplifiers-comparators 11 and to the amplifier-comparator 14. The output signal of the sensor of angular deviations 5 is supplied to the amplifier-comparators 15. The control circuit of the amplifiers-comparators generates control signals 3 and 4 (figure 2) at the moments when the input signals reach an extreme value (for example, a minimum). Comparator amplifiers respond to an input signal when, for example, there is a high level at the gate input and vice versa. Thus, the amplifier-comparators are switched on alternately and form a sequence of pulses 5 and 6 (figure 2), not coinciding in time. The leading edges of the output pulses of the amplifiers-comparators 14 and 15 (Fig. 1) start the precision single-shots 16 and 17, generating pulses 7 and 8 (Fig. 2) with a highly stable duration T. From the outputs of the precision single-shots, the pulses are fed to the input of the time-slot selection circuit 18 (figure 1), which generates two sequences of pulses 9 and 10 (figure 2). The duration of pulses 9 is equal to the difference between the trailing edge of pulse 7 of the one-shot 16 and the leading edge of the output pulse 8 of the second one-shot 17. The duration of pulses 10 is equal to the difference between the trailing edge of the pulse 8 of one-shot 17 and the leading edge of the pulse 7 of one-shot 16. From the output of the time-domain allocation circuit, pulses 9 and 10 go to the logical elements And 20 and 21 (Fig. 1), where they are filled with quantizing pulses with a period T _to from the generator 19. From the logical element 20, the pulse train N ₁ =

arrives at the summing input of the reverse counter 22 (figure 1), and from the output of the element 21, the pulse packet N ₂ =

to the subtracting input of this counter. At the output of the reversible counter, readings N = N ₁ -N _{2 are set} , which are proportional to the difference in the pulse durations 9 and 10 and, accordingly, to the flow rate of the controlled medium through the primary converter.

Indeed, from the time diagrams (figure 2) we have:
a = (T _o -T) + t _c (1)
b = (T _o -T) -t _c , where t _{c is the} time shift of the signals due to the action of the Coriolis force.

. (2)
В свою очередь связь между временным сдвигом t_c и массовым расходом контролируемой среды определяется выражением
t_c=S ˙ Q_м, (3) где S чувствительность первичного преобразователя, с²/кг. После подстановки из (3) в уравнение (2) получаем:
N

· Q_м (4)
Таким образом, в предложенном расходомере показания реверсивного счетчика N прямо пропорциональны массовому расходу контролируемой среды Q_м. Посредством устройства 23 (фиг. 1) эти показания преобразуются в стандартный выходной сигнал расходомера, например, 0-5 Ма постоянного тока.From the relations (1) it follows:
NN ₁ -N ₂ =

. (2)
In turn, the relationship between the time shift t _c and the mass flow rate of the controlled medium is determined by the expression
t _c = S ˙ Q _m , (3) where S is the sensitivity of the primary transducer, s ² / kg. After substituting from (3) into equation (2) we get:
N

Q _m (4)
Thus, in the proposed flow meter, the readings of the reversible counter N are directly proportional to the mass flow rate of the controlled medium Q _m . By means of the device 23 (Fig. 1), these readings are converted into a standard output signal of the flow meter, for example, 0-5 Ma DC.

 The counter-divider 12 and the control logic 13 (Fig. 1) generate control signals that synchronize the operation of the measuring transducer and at the same time set the number of measurement cycles.

 For small ranges of flow measurement, accordingly, the number N will be small and an increased number of measurement cycles is required and vice versa.

· Q_м
(5) где К коэффициент преобразования, Ма-/имп.Given the above, the output signal of the flow meter will be determined by the equation
I _out = n · K · N

Q _m
(5) where K is the conversion coefficient, Ma- / imp.

 As follows from the time diagrams of work (figure 2), the proposed device implements a differential method for converting mutual time shifts of signals.

 Improving the accuracy of flow measurement is achieved by eliminating errors from the "dead zone" effect and non-linear distortion of signals by fine-tuning the thresholds of the amplifiers-comparators to the electrical neutral of the input signals.

Claims (1)

 VIBRATION CORIOLIS FLOW METER, comprising a primary transducer with a sensing element, first and second angular deviation sensors, an electromagnetic vibrator, the power and measuring coils of which are connected to the oscillation excitation circuit, and a measuring transducer that includes two amplifier-comparators, the inputs of which are connected to the outputs of the angular sensors deviations, a time interval allocation scheme, the first output of which is connected to the second input of the first logical element AND, and the second output with dinene with the input of the counter-divider and with the second input of the second logical element And, the reversible counter, summing and subtracting the inputs of which are connected, respectively, with the outputs of the first and second logical elements And, and the output is connected to the input of the output signal generating circuit, a quantizing pulse generator, the output of which is connected to the first inputs of the AND logic elements and to the first input of the control logic circuit, the second input of which is connected to the output of the counter-divider, and the output is connected respectively to the control input a reversible counter and an output signal generating circuit, characterized in that, in order to increase the accuracy of the flow measurement, a comparator amplifier control circuit and two precision single-vibrator circuits are additionally introduced into the measuring transducer, the input of the amplifier-comparator control circuit connected to the first angular deviation sensor, and its outputs are to the gate inputs of the comparator amplifiers, the outputs of which are connected through precision single-vibrators to the inputs of the time slot allocation circuit.