JPH0478125B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an electromagnetic flowmeter converter having an improved calibration means of a signal processing section.

[Technical background of the invention]

In general, an electromagnetic flowmeter includes a detector that outputs a voltage signal proportional to the magnetic flux density in the measuring tube and the flow rate of the fluid, and a detector that amplifies the voltage signal detected by this detector to produce a flow rate proportional to the fluid flow rate. It consists of a signal converter that converts into a signal and outputs it, but in order to obtain a highly accurate flow rate signal from the signal converter, the signal processing section including the amplifier section must operate stably over a long period of time. It is essential to maintain the

By the way, the detector detects and outputs the flow rate using a pair of electrodes in the measuring tube, but normally, the electrochemical action (battery action)
As a result, DC and low frequency component noise is generated, which is superimposed on the flow rate output that should be measured and output. Therefore, as a means to separate the flow rate output and electrochemical noise, for example, alternately supply positive and negative excitation currents to the excitation coil installed in the measurement tube, and wait until the magnetic flux in the measurement tube stabilizes. The configuration is such that a signal converter samples the flow rate output and amplifies and outputs it. Furthermore, by making the detector and the signal converter AC-coupled, the input side impedance of the signal converter is set to a high impedance, so that the signal converter is not easily affected by the electrical conductivity of the fluid.

FIG. 6 is a diagram showing a configuration in which a calibration means is added to such a conventional signal converter. That is, the signal converter converts the flow rate outputs S1a and S1b (see Figure 7) taken out from a pair of electrodes of the detector into a capacitor.
The signal is supplied to a signal processing unit 5 through buffer amplifiers 1 and 2 having AC coupling means using Ca and Cb and resistors 3 and 4, where it is converted into a flow rate signal and output.

On the other hand, the signal converter calibration means includes switch circuits 6a and 6b that selectively input the detector flow rate output and the calibration simulation signal to the input terminals of the buffer amplifiers 1 and 2.
is provided, and a simulated signal is supplied from a DC power supply 9 to the calibration input contact side of these switch circuits 6a, 6b via switch circuits 7a, 7b which are turned on and off in accordance with a timing signal, and buffer amplifiers 8a, 8b. It is becoming.

[Problems with background technology]

However, since the simulated signal output by the above calibration means does not contain the electrochemical noise mentioned above, when the switch circuits 6a and 6b are switched to either the calibration side or the flow rate measurement side, , a large fluctuation in the DC level occurs in the capacitors Ca and Cb at the input end of the signal converter, which temporarily causes a saturation phenomenon in the buffer amplifiers 1 and 2 and the amplifiers included in the signal processing section 5, causing problems in calibration and flow rate. There is a problem that measurement is impossible.

[Purpose of the invention]

The present invention has been made with attention to the above points, and is an electromagnetic device that can supply a simulated signal to a signal processing section without changing the DC level of the signal converter input and without affecting flow measurement. The purpose of the present invention is to provide a flow meter converter.

[Summary of the invention]

The present invention provides an electromagnetic flowmeter converter that introduces the output of a flow rate detector into a signal processing section via a buffer amplifier and a resistor to obtain a flow rate signal, and in which a simulated signal generating means is connected to the input end of the signal processing section via a switch circuit. , and turns on the switch circuit in synchronization with the timing signal during a period when the excitation current is supplied to the excitation coil at a constant value, thereby generating a simulated signal from the simulated signal generating means. .

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIG. In the same figure, 10 is a detector that takes out a voltage signal proportional to the magnetic flux density in the measuring tube and the flow rate of the fluid. A pair of electrodes 12a, 12b and measurement tube 11
It consists of an excitation coil 13 installed in the excitation coil 13. For example, positive and negative constant currents are alternately supplied to the excitation coil 13 to generate magnetic flux in the measurement tube, and a voltage signal that intersects with this magnetic flux and is induced in the fluid. A pair of electrodes 1
It is designed to be taken out at 2a and 12b.

Reference numeral 20 denotes a signal converter with a calibration means for converting the voltage signal output from the detector 10 into a desired flow rate signal, and the signal converter includes buffer amplifiers 21 and 2 at each electrode output terminal as in the conventional case.
2 and the signal processing section 25 via the resistors 23 and 24.
The input end of is connected. This signal converter also includes an excitation switch circuit 26 and a constant current source 2.
7 connected in series, an excitation switch circuit 28, and a constant current source 29.
and a second excitation current supply means formed by connecting in series, both of these excitation supply means are connected in parallel to the excitation coil 13, and from the timing signal generation circuit 30 to the AND circuit 31 and the inverter 3.
A timing signal for alternately on/off control is applied to the switch circuits 28 and 26 via the AND circuit 33 and the like.

Next, the calibration means connects the resistor 23 and one input terminal of the signal processing section 25 and the other input terminal of the signal processing section 125 through calibration switch circuits 41 and 42, respectively. A current source 43 is connected. Further, it has a switch control circuit 45 and a control signal generation section 48 as a calibration control means for controlling on/off of the switch circuits 41 and 42 to generate a simulated signal. In addition, it is constituted by a first AND circuit 46, an inverter 32, a second AND circuit 47, etc., and each AND circuit 46,
Reference numeral 47 receives timing signals of opposite levels from the timing signal generating circuit 30 to alternately turn on and off the switch circuits 42 and 41. Further, the control signal generating section 48 has a function of setting the AND circuits 46 and 47 to an operable state when the operation of the AND circuits 31 and 33 is prohibited via the inverter 49.

Next, the operation of the electromagnetic flow meter converter configured as above will be explained. First, in the case of flow rate measurement, a low level signal S10 is generated from the control signal generator 48 as shown in FIG. Therefore, low level signals are output from both AND circuits 46 and 47, and both switch circuits 41 and 42 are turned off. When the switch circuits 41 and 42 are off, the input impedance of the signal processing section 25 is very high, so no current flows through the resistors 23 and 24, and no voltage drop occurs. On the other hand, on the excitation current supply side, the low level signal S10 generated from the control signal generator 48 is inverted by the inverter 49 and becomes high level, and both AND circuits 31 and 33 are set to an operable state. . At this time, if the timing signal generation circuit 30 outputs the timing signal S11 as shown in FIG.
13 is outputted and applied to the switch circuits 28, 26, whereby the switch circuits 28, 2
6 repeats alternately on and off, excitation coil 13
is supplied with an excitation current S14 as shown in FIG. As a result, a magnetic flux similar to the excitation current S14 is generated in the measuring tube 11, and when a conductive fluid acts on this magnetic flux, an electromotive force is generated in the fluid according to Fleming's law, and the pair of electrodes 12a, 12
From b, signals S15 and S16 as shown in FIG.
is taken out, impedance-converted with an amplification degree of 1 by buffer amplifiers 21 and 22, and supplied to the signal processing section 25. Here, both signals S15, S
16 differential voltages are taken out in synchronization with the timing signal S11, amplified, and output as a flow rate signal.

Next, the calibration operation will be explained with reference to FIG. In this case, the control signal generator 48 generates a high level signal S20, which causes the output terminal of the inverter 48 to go low level, and the output terminals of both AND circuits 31 and 33 to go low level, causing the switch to switch. Turn off circuits 28 and 26. Therefore, when the switch circuits 28 and 26 are in the OFF state, no exciting current flows as shown in S23 shown in FIG. 3, and no magnetic flux is generated within the measuring tube. Since there is no magnetic flux inside the measuring tube, the fluid flows through the measuring tube 11.
No voltage signal proportional to the flow rate is generated even if the flow is caused by electrochemical noise S at the electrodes 12a and 12b.
Only S24 and S25 occur.

On the other hand, the AND circuits 46 and 47 are set to an operable state, and at this time the timing signal generation circuit 30
Since high-level signals are alternately input from the AND circuits 46 and 47 via the inverter 32 and directly, the switch circuits 41 and 42 are
21 and S22, the constant current source 43 alternately turns on and off, and a simulated signal is applied to each input terminal of the signal processing section 25. That is, when the switch circuit 41 is in the on state, current flows from the constant current source 43 to the resistor 23, causing a voltage drop.
Since there is no voltage drop when it is turned off,
A signal S26 as shown in FIG. 3 appears, and the switch circuit 42 performs the same operation as S27.
Signals such as S26 and S26 appear, and these signals S26, S
27 is supplied to the signal processing section 25.
These signals S26 and S27 are the signals S15 and S27 in FIG.
It can be seen that it is similar to S16 and can be used as a simulated signal. Also, since the voltage drop corresponds to the flow rate signal, this voltage drop must be accurate, but the constant current source 43 can be made with high precision relatively easily by using Zener diodes, operational amplifiers, resistors, etc. can do.

Therefore, the configuration of the embodiment as described above has the following effects. That is, usually
Electrochemical noise of about 100 times the flow rate signal is generated from the pair of electrodes 12a, 12b, but with conventional calibration means, an excessive DC level change occurs on the input side of capacitors Ca, Cb when switching the switch circuits 6a, 6b. This caused problems such as saturation of the amplifier, making measurement and calibration impossible.

In contrast, the signal converter calibration means of the present invention only provides a reference voltage drop from the electrochemical noise level during calibration, so there is almost no fluctuation in the DC level and the signal processing section 25 is saturated. This will no longer happen. Therefore, it is possible to perform measurement and calibration by instantly switching between flow rate measurement and calibration, and it is also possible to automatically perform calibration during flow rate measurement using, for example, a microprocessor, resulting in higher accuracy. An electromagnetic flowmeter can be realized. In addition, if automatic calibration becomes possible, there is no need to use high-precision calibration parts that affect the amplification level in the signal processing section 25, etc., and the microprocessor itself can perform corrections, so the signal converter The cost can be significantly reduced.

In the above embodiment, the simulated signal is applied to both input terminals of the signal processing section 25, but if the signal processing section 25 is a differential amplifier, one input terminal is directly connected to the electrode, and the other input terminal is connected directly to the electrode. Only buffer amplifier 2
2. Exactly the same result can be obtained by connecting via the resistor 24. However, in order to obtain a signal value equivalent to that obtained when applying simulated signals to both input terminals of the signal processing section 25, the current values of the resistor 24 and the constant current source 43 must be doubled. Further, as shown in FIG. 4, the first stage amplifier is an AC buffer amplifier. Usually resistance 51
54 and capacitors 55 to 58 are selected so as not to affect the amplification degree of the flow rate signal frequency, so that although the buffer is outside the calibration loop, there is no problem in practice. Furthermore, when the differential amplifier constituting the signal processing section 25 is composed of an operational amplifier 251 and a resistor 252, the switch circuit 41 is connected only to one input terminal of the signal processing section 25, as shown in FIG. A constant current source 43 may be connected through the signal processing section 25 to provide a simulated signal to one input terminal of the signal processing section 25. In this case, the other input terminal of the signal processing section 25 is grounded via a resistor 61. Therefore, if you configure it like this,
Signal processing unit 25 as voltage drop resistors 23 and 24
The resistors that make up can be used in combination. Further, in the above embodiment, the excitation current is set to zero at the off time, but a predetermined current may be supplied at the off time. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

〔Effect of the invention〕

As described in detail above, according to the present invention, a simulated signal generating means is provided at the input end of the signal processing section via a switch circuit, and the switch circuit is excited during the period when the supply of exciting current to the exciting coil is cut off. The switch circuit is controlled on/off in synchronization with the timing signal used for current supply timing, and a simulated signal is supplied to the input terminal of the signal processing section, so that the DC level can be changed by switching. It is possible to provide an electromagnetic flowmeter converter that has almost no fluctuations, can be automatically calibrated during flow rate measurement, and is capable of highly accurate flow rate measurement in a stable state over a long period of time.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of an electromagnetic flowmeter converter according to the present invention, Figs. 2 and 3 are waveform diagrams explaining operations during flow measurement and calibration, and Figs. 4 and 5. FIG. 6 is a configuration diagram illustrating a modification of the present invention, FIG. 6 is a configuration diagram of a conventional device, and FIG. 7 is a waveform diagram illustrating the operation of the conventional device. 10...detector, 12a, 12b...electrode, 1
3... Excitation coil, 20... Signal converter, 25...
...Signal processing unit, 30...Timing signal generation circuit, 41, 42...Switch circuit, 43...Constant current source, 45...Switch control circuit, 49...Control signal generation section.

Claims (1)

[Claims] 1. Two or more excitation currents with different polarities or current values are periodically supplied to an excitation coil, whereby the output of a flow rate detector taken out from a pair of electrodes is transmitted through a buffer amplifier and a resistor. In an electromagnetic flowmeter converter that obtains a flow rate signal by introducing it into the signal processing section through
Calibration control means for supplying excitation current to the excitation coil at a constant value and outputting a switch switching control signal in synchronization with a timing signal during the constant value period; and switch switching control obtained by the calibration control means. An electromagnetic flowmeter converter comprising simulated signal generating means for receiving a signal and turning on a switch circuit to supply a simulated signal of a predetermined level to an input terminal of the signal processing section. 2. The calibration control means maintains the supply of excitation current to the excitation coil at a constant value, and includes a control signal generation section that outputs an operable signal during the constant value period, and receives an operation enable signal from the control signal generation section. and a switch control circuit which is set to an operable state and receives the timing signal and outputs a switch switching control signal.
The electromagnetic flowmeter converter described in Section 1. 3. The electromagnetic flow meter converter according to claim 1, wherein the simulated signal uses a constant current source. 4. The electromagnetic flowmeter converter according to claim 1, wherein a switch circuit is provided corresponding to each input terminal of the signal processing section. 5. The electromagnetic flowmeter converter according to claim 1, wherein the switch circuit is provided at one input end of the signal processing section. 6 The calibration control means adjusts the supply timing of the excitation current and the generation timing of the simulated signal to N:1 (N
2. The electromagnetic flowmeter converter according to claim 1, wherein the signal processing section is calibrated by continuously controlling the signal processing section at a rate (integer).