JPS5847214A - Square wave exciting electro-magnetic flow meter converter - Google Patents

Abstract

PURPOSE:To detect the flow-out of liquid in a detector by providing a three- way selection switch that shuts off an exciting circuit by means of giving a mimic signal that is synchronized with the exciting signal to the exciting circuit and providing a comparator that takes as a standard voltage the output of a converter at the time where there is a fluid. CONSTITUTION:A square wave exciting electro-magnetic flow meter converter consists of a high input impedance differential A/C amplifier 11, later stage amplifier 12 that processes the output by calculation. Further, a mimic signal generating circuit that consists of a switch 14 such as FET that is turned on and off in synchronization with the exciting signal, D/C standard voltage source 13, and resistor 15 for current limitation is provided. Also a 3-circuit select switches 19a-c and a comparator 21 are provided. The standard voltage 20 is established equal to the output value of an amplifier 12 that is obtained by input of a mimic signal when the switches 19a-c are operated and a fluid exists in the measurement pipe 3 and the output impedance of the electrode 4 is at maximum, and it is possible to make a comparator 21 sends a signal that indicates that there is no liquid in the measurement tube 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic flowmeter, and more particularly to an electromagnetic flowmeter converter having a function of detecting the presence or absence of fluid in a measurement pipe of a square wave excitation electromagnetic flowmeter detector.

Figure 1 shows the electromagnetic flowmeter detector (hereinafter referred to as the detector) (1).
The block diagram of the electromagnetic flowmeter which consists of and an electromagnetic flowmeter converter (hereinafter referred to as a converter) (5) is shown. The detector (1) consists of an excitation coil (2) and an electrode (4) installed in the measuring tube (3) to detect the electromotive force generated in the fluid, and the voltage between the electrodes is determined by the high input of the converter (5). It is amplified by an impedance differential AC amplifier (6), and usually 4 to 2
0 m A I) It is output as a unified signal of C.

FIG. 2 shows an equivalent circuit of the input signal. In the figure, (8) is a common-mode noise voltage source that appears in the same phase between the electrodes, and (9).

(9') is a signal voltage source proportional to the flow rate, and a resistance (I
I.

(10') indicates the output impedance, which is mainly determined by the conductivity of the fluid and the size of the electrode.

When a detector is actually installed, the fluid inside the detector often leaks due to piping or the installation method itself, which undergoes large changes in flow rate and pressure. When the fluid in the detector is discharged, the signal power supplies (9) and (9') become zero and the output impedance (IL (10') i becomes infinite in Fig. 2.The differential AC amplifier ( 6) is especially problematic because under ideal conditions, such as no influence of external noise, the output value will be zero, indicating that there is no fluid, that is, the flow rate is zero.However, normally, commercial power supply The differential AC amplifier (6) may become saturated due to the influence of the converter and the excitation power supply, resulting in the inconvenience that the output value of the converter does not become zero, leading to the misunderstanding that fluid is flowing. .

Conventionally, the following countermeasures have been taken against such problems. One example is as shown in Figure 3, where a resistor (i) is connected between each input of the differential AC amplifier (6) and the ground.
ll, (11') to lower the impedance. As a result, even if the fluid escapes, the impedance of the input section does not increase, and the output value becomes zero without being affected by noise. The disadvantage of this method is that when the conductivity of the fluid changes, the output value of the converter changes as the trench impedance changes, so it is only applicable when the conductivity of the fluid is not too low and changes little. It is impossible.

It is not possible to determine whether the fluid is stationary or absent from the output of the converter alone.

Another example is a method in which a pressure gauge is attached to a measuring tube and the leakage of fluid is detected based on the pressure inside the tube. Normally, when fluid flows, pressure is generated, so if there is no pressure rise and the output of the converter fluctuates, you can tell that there is a fluid leak1.The disadvantage of this method is that it requires extra instruments such as a pressure gauge. be.

The purpose of the present invention is to easily detect the leakage of fluid in the detector without preparing a separate measuring device by using a device on the converter side, and also to easily detect a drop in performance by lowering the input impedance of the converter. . However, the purpose of the lever is to provide a simulation signal generation circuit that has a switch that turns on and off in synchronization with an excitation signal, a DC reference voltage source, and a resistor, and generates a simulation signal of the input signal to the converter, and an output signal of this circuit. a three-circuit selector switch that connects the converter to one input of the converter, connects the other input of the converter to ground, and interrupts the excitation circuit; and when the selector switch is activated, the output voltage of the converter changes. , when there is a fluid in the measurement tube and the output impedance of the pair of electrodes is at its highest value, the simulated signal is input and the output value of the converter is compared with a reference voltage determined to be equal to the output value of the converter. and a comparator that outputs a signal indicating that there is no fluid in the measuring pipe when the flow rate exceeds 1, and the three-circuit changeover switch can switch between a flow rate measurement operation and an operation for detecting the presence or absence of fluid in the measuring pipe. This was achieved by

Embodiments of the present invention will be described below with reference to the drawings. Fourth
The figure shows the configuration of a square wave excitation electromagnetic flowmeter converter according to an embodiment of the present invention. The square wave excitation electromagnetic flow meter converter includes a high input impedance differential AC amplifier (Ll) and a post-stage amplifier t121. The excitation circuit (la) is the same as before.The following elements are attached to this electromagnetic flowmeter converter.Switch a4, which is usually made of a semiconductor such as an FET, which turns on and off in synchronization with the excitation signal) , a DC reference voltage source (13), and a simulated signal generation circuit that generates a simulated signal of the input signal to the stain magnetic current pointer converter, which includes a resistor QE9 that limits the reference voltage that is turned on and off to a predetermined current value.

Still, the switch (19b) that connects the output signal of this simulated signal generation circuit to one input of the converter, the switch (19a) that connects the other input of the converter to the ground, and the output of the excitation circuit 08) are cut off. A three-circuit changeover switch Ql consisting of a switch (19c) is provided. Further, a downstream amplifier (a comparator C11 for comparing the output of the second one with a reference voltage -) is provided after the converter.

In the electromagnetic flowmeter converter according to the embodiment of the present invention configured as described above, when the three-circuit changeover switch member is in the state shown in the figure, that is, in normal flow rate measurement operation, all <conventional square wave excitation> It is clear that it works as an electromagnetic flowmeter transducer. Figure 5 shows the excitation signal (2
Figure (a) shows the high impedance differential AC amplifier 0]
) The output signal (c) of the detector Q7) appearing at the input is shown in figure (b). (b) It is common to sample the wave height value of the shaded area shown in the figure and output it as a flow rate signal.

When the 3-circuit selector switch Q is switched to detect the leakage of fluid in the measuring tube of the detector, the differential AC amplifier α
One end of the input of υ is connected to ground by the switch (19a), the other end is connected to one resistor by the switch (19b), and the output of the excitation circuit 0 is cut off by the switch (19c). No excitation coil (2) is not excited,
No flow signal is generated at the electrode (3) in the detector 07).

At this time, the voltage waveform (
24) is shown in FIG. 5(c). Fig. 5 (C1 is expressed based on the upper input of the differential AC amplifier (11) in Fig. 4. A negative square wave voltage is applied to the lower input. However, the differential AC amplifier αη Since it is an AC amplifier, the output is equivalent to the waveform shown in Figure 5(d) (2■ is added. The peak value of this input waveform is 7, V, Ro/R,, 10R8-( 1, ).Here, vl is the voltage of the reference voltage source Q, Ro is the series combined resistance value of the output impedance θL (10') shown in Fig. 2, and R1 is the resistor (one resistance value). .Excitation frequency is 1
Since the voltage is low, below 0H2, and the voltage value is stable, you can consider only the resistor and output impedance without considering the capacitance.

The output of an electromagnetic flowmeter converter is proportional to the peak value of the input waveform, so when the three-circuit selector switch is switched, the output value is proportional to the reference voltage 1 to R, according to equation (1). > 1
(If , o, then it is also proportional to R6. Also, equation (1) shows that ■ By appropriately selecting the values of 1 and R, an output value similar to the flow rate signal can be obtained without changing the amplification degree of the converter. This indicates that the

Therefore, when there is fluid in the measuring tube of the detector, R8
The highest value of is determined in advance, and the output value of the converter is determined when the output of the simulated signal generation circuit is inputted to a converter having a constant gain with vl r R4 set to an appropriate constant. Then, this output value is set as a voltage value, and this is set as a voltage value by the comparator C.
Let the reference voltage of υ be −.

In the electromagnetic flowmeter converter of the embodiment of the present invention set and configured as described above, when switching from the normal flow rate measurement operation to the operation for detecting the presence or absence of fluid in the measurement pipe using the 3-circuit changeover switch Q9) Ic, the output voltage of the converter When the value exceeds the reference voltage (20), it means that the previous R8 is larger than the predetermined maximum value, and if there is no fluid in the measuring tube, the output of comparator 01+ at this time. This allows you to know if there is fluid leakage in the detector.

As is clear from the above explanation, the electromagnetic flow control converter according to the present invention does not require any changes such as changing the gain of the converter in order to detect the presence or absence of fluid in the detector, and does not require any change in the gain of the converter. The presence or absence of fluid in the detector can be determined by simply adding a few additional electrical parts and without requiring other measurement instruments such as pressure gauges or cables to connect them. Furthermore, since it works exactly the same as a conventional converter during flow measurement operation, there is no performance deterioration due to a reduction in converter input impedance. In the embodiment shown in FIG. 4, a three-circuit changeover switch is used, but a relay can also be used, and since there is no need to change the gain of the converter, it is easy to detect the presence or absence of fluid in the detector by remote control.

Next, FIG. 6 shows another embodiment of the present invention. In this embodiment, the excitation signal is frequency-divided by the frequency divider QO, and the frequency-divided excitation signal is used to generate the time required to detect the presence or absence of fluid only when a positive signal is received from the pulse generator ■η. Generates a one-shot pulse that turns on the relay (c). Then, while the one-shot pulse is generated [7], the relay ce is turned on to perform the fluid detection operation, and the flow rate signal is outputted from the track hold circuit at the value immediately before the fluid detection operation.

In the embodiment shown in Fig. 4, even though remote control was possible, fluid detection operation was not performed unless a signal was given manually.
In the illustrated embodiment, fluid sensing can be performed automatically.

In the embodiment shown in Fig. 6, the detection interval is determined by dividing the frequency of the excitation signal, so there is no need for a timer, and the flow rate signal also uses a hold circuit to detect the fluid. I try to keep it as low as possible.

As detailed above, according to the present invention, fluid leakage in an electromagnetic flowmeter detector can be detected without preparing a separate measurement device.
Further, it is possible to provide a square wave excitation electromagnetic flowmeter converter that can perform detection by arbitrarily switching from flow rate measurement operation without degrading performance due to lowering the input impedance of the converter.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of the electromagnetic flowmeter's detector and converter, Figure 2 is a diagram showing the equivalent circuit of the input signal to the converter, and Figure 3 shows fluid leakage in the detector when it occurs. 4 is a block diagram showing the configuration of a square wave excitation electromagnetic flowmeter converter according to an embodiment of the present invention; FIGS. 5(a), (b), (c), (di are the excitation signal in Figure 4, the output signal of the detector appearing at the input of the differential AC amplifier, the voltage waveform between the inputs of the differential AC amplifier during fluid detection operation, and Figure 5 ( FIG. 6 is a block diagram showing the configuration of a square wave excitation electromagnetic flowmeter converter according to another embodiment of the present invention. 2. Excitation coil 3. - Measuring tube 4... Electrodes 10, 10'... Output impedance 11... High input impedance differential AC amplifier 12... Post-stage amplifier 13... DC reference voltage source 14... Switch
15...Resistor 17...Detector 18...
・Excitation circuit 19...3 circuit changeover switch 20...
Reference voltage 21... Comparator 26... Frequency divider 27... Hals generator 28... Relay 29... Track hold circuit agent Patent attorney Inoue - Male

Claims (1)

[Claims] A constant magnetic field is applied at a predetermined period by an excitation coil perpendicular to the tube axis of the measuring tube, and the voltage generated in the conductive fluid flowing inside the measuring tube is extracted by an electrode.The voltage at the point when the magnetic field stabilizes before the polarity reverses. In a square wave excitation electromagnetic flowmeter converter that samples and amplifies the signal and outputs it as a flow signal, there is a switch that turns on and off in synchronization with the excitation signal,
a simulation signal generation circuit that generates a simulation signal of the input signal to the converter; an excitation circuit that connects the output signal of this circuit to one input of the converter and connects the other input of the converter to ground; a three-circuit changeover switch that cuts off the output of the converter; and a three-circuit changeover switch that cuts off the output of the converter when the changeover switch is activated, and a simulated signal that changes the output voltage of the converter when fluid is present in the measurement tube and the output impedance of the electrode is at its highest value. Compare with a reference voltage set equal to the output value of the converter obtained by inputting it! ~ A comparator that outputs a signal indicating that no fluid is present in the measuring tube when this voltage is exceeded.