JPS606734Y2 - Check device for electromagnetic flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a check device for checking the operation and calibrating the span of an electromagnetic flowmeter converter that performs low-frequency rectangular wave excitation.

Fig. 1 is a principle configuration diagram showing an example of an electromagnetic flowmeter in which a check device according to the present invention is used, in which 1 is an electromagnetic flowmeter transmitter, 2 is a conduit through which the fluid to be measured passes, and 3 and 4 are connected to the conduit 2. The electrodes provided, 5 is an exciting coil, 6 is a current transformer, 7 is a switch, 8.9 is a rectifier, 10 is a resistor, 11 is an electromagnetic flowmeter converter, and 12 is a flow rate signal generated between electrodes 3 and 4. A signal amplifier for amplification, 13 a dividing circuit, 14 an output circuit, 15 a switch drive circuit, and 16 a commercial power source.

The configuration of this electromagnetic flowmeter is as follows.

The commercial power source 16 is connected to the input end of the rectifier 8 via the switch 7 and the primary winding 6a of the current transformer 6.

The output end of the rectifier 8 is connected to the excitation coil 5.

The electrodes 3 and 4 are connected to the input end of a signal amplifier 12, and the output end of the signal amplifier 12 is connected to one input end of a divider circuit 13.

The secondary winding 6b of the current transformer 6 is connected to the input end of a rectifier 9, and the output end of the rectifier 9 is connected to a resistor 1o.
A comparison signal generated across the resistor 10 is input to the other input terminal of the divider circuit 13.

The output terminal of the division circuit 13 is connected to the input terminal of the output circuit 14.

FIG. 2 is a waveform diagram for explaining the operation of the electromagnetic flowmeter shown in FIG. is the current waveform flowing through the primary winding 6a of the current transformer 6,
5 is a comparison signal waveform generated between both ends of the resistor 10, 6 is a zero volt detection signal waveform that detects the voltage of the commercial power supply 16 near zero volts and becomes a low level, and 7 and 8 are sample signal waveforms.

The operation of this electromagnetic flowmeter is as follows.

The switch 7 is driven ON-OFF at the timing when the frequency of the commercial power supply 16 is divided as shown in waveform 2.

As a result, an exciting current as shown in waveform 3 flows through the exciting coil 5.

Here, the current flowing through the primary winding 6a of the current transformer 6 is as shown in waveform 4, and the comparison signal does not match the excitation current when the commercial power supply voltage is near zero volts and has an error, as shown in waveform 5.

This means that when the commercial power supply voltage is around zero volts, the excitation coil 5
Although no current is supplied from the commercial power supply 16 to the excitation coil 5, the excitation current flows through the rectifier 8 due to its own back electromotive force.

By the way, if the flow rate signal from the signal amplifier 12 is divided by the comparison signal from the resistor 10 in this state, an error will occur in the output.

As one method to compensate for this error, this electromagnetic flowmeter detects the commercial power supply voltage near zero volts, and samples the flow rate signal and comparison signal using the timing signals shown in waveforms 7 and 8, excluding the near zero volts. Then, division is performed between these sampled signals.

As a check device for performing operation check and span calibration in such an electromagnetic flowmeter, it is desirable to obtain simulated signals close to the signals of waveform 3 and waveform 5.

In particular, in order to confirm the operation using the sample signals shown in waveforms 7 and 8, a simulated signal having a waveform as shown in waveform 5 is required.

However, conventional checking devices convert the commercial power supply into a low-frequency rectangular wave signal using a frequency divider, use this signal as a simulated comparison voltage signal, and divide the voltage using a resistor divider to generate a simulated flow rate signal. Ta.

In such a conventional check device, both the simulated comparison signal and the simulated flow rate signal are rectangular waves with a fast rise and no ripple and no distortion.

Therefore, such conventional check devices are insufficient to meet the above requirements when used in the transmitter of an electromagnetic flowmeter as shown in Fig. 1, and the present invention is an improvement on these points. .

FIG. 3 is a circuit diagram showing an embodiment of the checking device according to the present invention, in which 17 is a switch, 18 and 24 are current transformers, 19.20 is a rectifier, 22.23 is a coil and a resistor as a simulated load, and 29 is the span adjustment volume, 3
4.35 is a common mode check switch, 36 is a span setting switch, 38 is a span setting volume, and 39 is a zero point setting switch.

The configuration of this checking device is as follows.

A commercial power source 16 is connected to the input end of a rectifier 19 via a switch 17 and a primary winding 18a of a first current transformer 18.

A series circuit of a coil 22 and a resistor 23 is connected to the output end of the rectifier 19, and a primary winding 2 of a current transformer 24 is connected to the output terminal of the rectifier 19.
A series circuit of 4a and a diode 25 is connected.

A secondary winding 18b of the current transformer 18 is connected to an input end of a rectifier 20, and an output end of the rectifier 20 is connected to a resistor 21.

A diode 26 is connected to the secondary winding 24b of the current transformer 24, and a series circuit of a diode 27 and a resistor 28 is also connected.

One end of the resistor 28 is connected to the resistor 21, and the other end is connected to the span adjustment volume 29. Resistance 30.31, 32a to 32n,
It is connected to a common potential through 33 series circuits.

Common mode check switches 34 and 35 are connected to the resistors 31 and 33.

Both ends of each resistor 32a to 32n are span setting switches 36
selected by resistor 37 and span setting volume 38
connected to a parallel circuit.

Sliding terminal of span setting volume 38 and resistor 32n, 3
A zero point setting switch 39 is connected between the connection point No. 3 and the connection point No. 3.

FIG. 4 is a waveform diagram for explaining the operation of the check device shown in FIG.
Current waveform flowing through 3, 4 is the first current transformer 18
5 is the waveform of the simulated comparison signal generated between both ends of the resistor 21, 6 is the current waveform flowing through the primary winding 24a of the second current transformer 24, and 7 is the waveform of the current flowing through the primary winding 24a of the second current transformer 24. The current waveform generated in the secondary winding 24b of the current transformer 24, 8 the signal waveform generated between both ends of the resistor 28, 9 the sliding terminal of the span setting volume 38 and the resistor 32
This is a simulated flow rate signal waveform generated between the connection point a and 33.

The operation of the checking device shown in FIG. 3 is as follows.

The switch 17 receives the ON-OFF drive signal from the switch drive circuit 15 of the converter 11 shown in FIG. 1 (waveform 2 in FIG. 4).
A current shown in waveform 3 flows through the simulated loads 22 and 23 under the control of .

A current shown in waveform 4 flows through the primary winding 18a of the first current transformer 18, and a current shown in waveform 5 flows between both ends of the resistor 21.
The simulated comparison signal shown in is obtained.

Further, the primary winding 24a of the second current transformer 24 has a commercial power supply voltage near zero volts and the switch 17 is OFF.
Immediately after , a current shown in waveform 6 flows.

Since this current shown in waveform 6 includes a DC component, it is transmitted to the secondary winding of the second current transformer 24 as the current shown in waveform 7, and a signal shown in waveform 8 is obtained across the resistor 28. .

The sum of the simulated comparison signal generated across the resistor 21 and the signal generated across the resistor 28 is adjusted by the span setting switch 36 and the span setting volume 38 to obtain the simulated flow rate signal shown in waveform 9. .

Although some errors occur in the simulated flow rate signal shown in waveform 9 due to distortion of waveform 7, the ratio of waveform 8 to waveform 5 is 1.
%, which is medium to begin with, so this error is so small that it can be ignored.

Therefore, according to the present invention, a simulated flow rate signal proportional to the flow rate signal proportional to the excitation current shown in waveform 3 in Fig. 2 can be obtained as waveform 9 in Fig. 4, and a simulated flow rate signal proportional to the comparison signal shown in waveform 5 in Fig. 2 can be obtained. Since the simulated comparison signal is obtained as waveform 5 in FIG. 4, span calibration can be performed with sufficient accuracy.

Furthermore, since an accurate simulated comparison signal can be obtained, it is also possible to check the sample operation.

Note that this check device may be built into the converter, the excitation coil 5 of the transmitter 1 may be used as the simulated load 22, 23, and the switch 17 is inserted at the output of the rectifier 19. You can put it on the side.

Furthermore, in the case where the switch 7 is provided in the converter 11 in the electromagnetic flowmeter shown in FIG. It's okay.

Further, although the embodiment in FIG. 3 has a configuration that allows arbitrary span setting, the configuration may be simplified so that a simulated flow rate signal at only one point is output.

[Brief explanation of drawings]

Fig. 1 is a principle configuration diagram showing an example of an electromagnetic flowmeter in which the check device according to the present invention is used, Fig. 2 is a waveform diagram for explaining the operation of the electromagnetic flowmeter shown in Fig. 1, and Fig. 3 is a diagram of the present invention. FIG. 4 is a circuit diagram showing an embodiment of the checking device according to the invention, and FIG. 4 is a waveform diagram for explaining the operation of the checking device shown in FIG. 1... Electromagnetic flowmeter transmitter, 3, 4... electrodes,
5... Excitation coil, 6... Current transformer, 7... Switch, 11... Converter, 12... Signal amplifier, 13・・・・・・
Division circuit, 14... Song output circuit, 15... Switch drive circuit, 16... Commercial power supply, 17...
...Switch, 18...First current transformer, 22.23...Simulated load, 24...Second current transformer, 34.35...Common Mode check switch, 36...Span setting switch, 38...Span setting volume, 3
9...Track zero point setting switch.

Claims (1)

[Scope of utility model registration request] A first current transformer and a rectifier are provided between the excitation coil of the electromagnetic flowmeter converter or its simulated load and an AC power source that is intermittent at a low frequency by a switch, and a first current transformer and a rectifier are provided in parallel with the excitation coil or its simulated load. 2 current transformers are provided, and rectify the current signal of the same frequency as the AC power source generated in the secondary winding of the first current transformer to obtain a simulated comparison signal, and A checking device for an electromagnetic flowmeter, characterized in that a simulated flow rate signal is obtained by adding the simulated comparison signal to a current signal generated in the next winding.