JPS6261892B2 - - Google Patents

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 an electromagnetic flowmeter detector (hereinafter referred to as the detector) 1 and an electromagnetic flowmeter converter (hereinafter referred to as the converter).
5 shows a block diagram of an electromagnetic flowmeter consisting of 5. The detector 1 consists of an electrode 4 that detects the electromotive force generated in the fluid provided in the measurement tube 3 of the excitation coil 2, and the voltage between the electrodes is amplified by the high input impedance differential AC amplifier 6 of the converter 5. , which is normally converted into a unified signal of 4 to 20 mADC by the downstream amplifier 7 and output.

FIG. 2 shows an equivalent circuit of the input signal. In the figure, 8
is the common mode noise voltage source appearing in the same phase between the electrodes, 9.
9' is a signal voltage source proportional to the flow rate, and resistor 1
0 and 10' represent 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, 9' become zero and the output impedances 10, 10' become infinite in FIG. 2. If the differential AC amplifier 6 in the converter is 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, and there is no particular problem. However, normally, the differential AC amplifier 6 saturates due to the influence of the commercial power supply or excitation power supply, and the output value of the converter does not reach zero, leading to the misunderstanding that fluid is flowing. An inconvenience occurred.

Conventionally, the following countermeasures have been taken against such problems. One example, as shown in FIG. 3, is to connect each input of the differential AC amplifier 6 and the ground using resistors 11 and 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 the output value of the transducer changes when the conductivity of the fluid changes, that is, when the impedance changes, and it can only be applied when the conductivity of the fluid is not very low and changes little. . Furthermore, it is not possible to determine whether the fluid is stationary or absent based solely on the output of the converter.

Another example of countermeasure is to attach a pressure gauge to the measuring tube and detect the leakage of fluid based on the pressure inside the tube. Normally, when fluid flows, pressure is generated, so if there is no increase in pressure and the output of the converter fluctuates, it can be determined that there is a fluid leak. The disadvantage of this method is that it requires extra instruments such as pressure gauges.

An object of the present invention is to detect the leakage of fluid in a detector without preparing a separate measurement device by using a device on the converter side, and without deteriorating the 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 changeover 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 changeover 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 tube when the flow rate exceeds 1, and the three-circuit changeover switch can switch between the flow rate measurement operation and the operation of detecting the presence or absence of fluid in the measuring tube. This was achieved by

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows the configuration of a square wave excitation electromagnetic flowmeter converter according to an embodiment of the present invention. Square wave excitation electromagnetic flow meter converter is a high input impedance differential AC amplifier 1
1, a post-stage amplifier 12 for arithmetic processing of its output, and an excitation circuit 18 as before.
The following elements are attached to this electromagnetic flowmeter converter. Normal FET that turns on and off in synchronization with the excitation signal
A simulator that generates a simulated signal of the input signal to the electromagnetic flowmeter converter is composed of a switch 14 made of semiconductors such as a DC reference voltage source 13, and a resistor 15 that limits the reference voltage to be turned on and off to a predetermined current value. A signal generation circuit is provided. Further, there is a switch 19b that connects the output signal of the simulated signal generating circuit to one input of the converter, a switch 19a that connects the other input of the converter to the ground, and a switch 19c that cuts off the output of the excitation circuit 18. A circuit changeover switch 19 is provided. Furthermore, a downstream amplifier 12 of the converter
comparator 2 that compares the output of
1 will be provided.

The electromagnetic flowmeter converter according to the embodiment of the present invention configured as described above has a completely conventional square wave excitation electromagnetic flow rate when the three-circuit changeover switch 19 is in the state shown, that is, in normal flow rate measurement operation. It is clear that it works as a meter transducer. In Figure 5,
The excitation signal 22 generated by the excitation circuit 18 is shown in figure a.
The output signal 23 of the detector 17 appearing at both inputs of the high impedance differential AC amplifier 11 is shown in Figure b. It is common to sample the peak value of the shaded area shown in Figure b and output it as a flow rate signal.

When the three-circuit selector switch 19 is switched to detect the leakage of fluid in the measuring tube of the detector, one end of the input of the differential AC amplifier 11 is switched to the switch 19a.
The other end is connected to the resistor 15 by the switch 19b, and the output of the excitation circuit 18 is cut off by the switch 19c, so the excitation coil 2 is not excited and the flow rate signal is not transmitted to the electrode 3 in the detector 17. Does not occur. The voltage waveform 24 between the inputs of the differential AC amplifier 11 at this time is shown in FIG. 5c. Figure 5c shows the differential AC amplifier 1 in Figure 4.
It is expressed based on the upper input of 1,
A negative square wave voltage is applied to the lower input. However, since the differential AC amplifier 11 is an AC amplifier, the output is equivalent to the case where the waveform 25 shown in FIG. 5d is added. The peak value of this input waveform is 1/2V ₁ R ₀ /R ₁ +R ₀ (1). Here, V ₁ is the voltage of the reference voltage source 13, R ₀
is the output impedance 10,1 shown in Figure 2.
0' is the series combined resistance value, and R ₁ is the resistance value of the resistor 15. The excitation frequency is low at 10Hz or less, and the voltage value is also in a stable range, so you can consider only the resistance and output impedance without considering the capacitance.

Since the output of the electromagnetic flowmeter converter is proportional to the peak value of the input waveform, the output value when the three-circuit changeover switch 19 is switched is proportional to the reference voltage V ₁ from equation (1), and R ₁ ≫ R If it is ₀ , it is also proportional to R ₀ . Furthermore, equation (1) shows that by appropriately selecting the values of V ₁ and R ₁ , an output value similar to the flow rate signal can be obtained without changing the amplification degree of the converter.

Therefore, the maximum value of R ₀ when fluid is present in the measuring tube of the detector is determined in advance, and V ₁ and R ₁ are set to appropriate constants to convert the output of the simulated signal generation circuit to have a constant gain. Find the output value of the converter when input to the converter. Then, this output value is set as a voltage value, and this is set as the reference voltage 20 of the comparator 21.

In the electromagnetic flowmeter converter of the embodiment of the present invention set and configured in this manner, when the normal flow rate measurement operation is switched to the operation for detecting the presence or absence of fluid in the measuring pipe by the three-circuit changeover switch 19, the output voltage value of the converter changes. When the reference voltage exceeds 20, it means that the above-mentioned R ₀ is larger than the predetermined maximum value, that is, there is no fluid in the measuring tube, and the output of the comparator 21 at this time prevents fluid leakage in the detector. You can know.

As is clear from the above description, the electromagnetic flowmeter 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 the converter does not require any changes such as changing the gain of the converter. The presence or absence of fluid in the detector can be determined by simply adding an additional electrical component, without requiring other measuring instruments such as pressure gauges or cables to connect them. Also,
During flow measurement operation, it works exactly the same as a conventional converter, so 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 there is no problem with a relay, 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 frequency of the excitation signal is divided by a frequency divider 26, and the frequency-divided excitation signal is used to generate a pulse generator 2.
7, a one-shot pulse is generated that turns on the relay 28 for the time necessary to detect the presence or absence of fluid only when a positive signal is received, for example. and,
While the one-shot pulse is occurring, the relay 28
is turned on to perform a fluid detection operation, and the track hold circuit 29 outputs the flow rate signal at the value immediately before the fluid detection operation.

In the embodiment shown in FIG. 4, although remote control is possible, the fluid detection operation is not performed unless a signal is given manually, but in the embodiment shown in FIG. 6, fluid detection can be performed automatically. In the embodiment shown in Fig. 6, the detection interval is determined by dividing the excitation signal, so there is no need for a timer, and a hold circuit is also used for the flow rate signal to eliminate errors that occur during fluid detection. I try to minimize it as much as possible.

As described in detail above, according to the present invention, fluid leakage in the electromagnetic flowmeter detector can be detected without preparing a separate measurement device, and without deteriorating performance by lowering the input impedance of the converter. It is possible to provide a square wave excitation electromagnetic flowmeter converter that can detect by arbitrarily switching from .

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of an electromagnetic flowmeter consisting of a detector and a converter, Figure 2 is a diagram showing the equivalent circuit of the input signal to the converter, and Figure 3 is a diagram showing when fluid leaks in the detector. FIG. 4 is an electrical connection diagram showing a conventional example of malfunction prevention measures; FIG. 4 is a block diagram showing the configuration of a square wave excitation electromagnetic flow meter converter according to an embodiment of the present invention; FIG.
Figures a, b, c, and d are the excitation signal in Figure 4, the detector output signal appearing at both inputs of the differential AC amplifier, the voltage waveform between the inputs of the differential AC amplifier during fluid detection operation, and the fifth FIG. 6 is a time chart showing an input waveform equivalent to that in FIG. 2... Excitation coil, 3... Measuring tube, 4... Electrode, 1
0, 10'... Output impedance, 11... High input impedance differential AC amplifier, 12... Post-stage amplifier, 13... DC reference voltage source, 14... Switch, 1
5...Resistor, 17...Detector, 18...Excitation circuit, 1
9...3 circuit selection switch, 20...reference voltage, 21
... Comparator, 26... Frequency divider, 27... Pulse generator, 28... Relay, 29... Track hold circuit.

Claims (1)

[Claims] 1 Apply a constant magnetic field perpendicular to the tube axis of the measuring tube at a predetermined period using an excitation coil, extract the voltage generated in the conductive fluid flowing inside the measuring tube with an electrode, and measure the voltage at the point when the magnetic field stabilizes before the polarity reverses. In a square wave excitation electromagnetic flowmeter converter that samples, amplifies the signal, and outputs it as a flow rate signal, one end is connected to a DC reference voltage source, the other end is connected to one input of the converter, and the converter is turned on and off in synchronization with the excitation signal. and a switch that constitutes a dub signal generation circuit that generates a dub signal of the input signal to the converter with the DC reference voltage source, and an output signal of the dub signal generation circuit outputted through this switch. A three-circuit changeover switch that connects to one input of the converter, connects the other input of the converter to ground, and cuts off the output of the excitation circuit, and the output voltage of the converter when the changeover switch is activated. is compared with a reference voltage set equal to the output value of the converter obtained by inputting the simulated signal when a fluid exists in the measurement tube and the output impedance of the electrode is at its highest value. 1. A square wave excitation electromagnetic flow meter converter, comprising: a comparator that outputs a signal indicating that no fluid exists in a measuring pipe when the square wave excitation exceeds the limit.