JPS61225614A - Electromagnetic flowmeter convertor - Google Patents

Abstract

PURPOSE:To enable supply of a simulated signal without influencing flow measurement, and generating no fluctuation in DC-levels of a signal convertor input, by connecting a simulated signal generating means with on input end of a signal processing unit through a switch circuit. CONSTITUTION:Magnetic flux is generated by supplying positive and negative constant current alternately to an exciting coil 13 set in a measuring pipe 11 and a voltage signal induced in liquid in an intersected condition with this magnetic flux is taken out by electrodes 12a, 12b. On the other hand, simulated signal generating means 45, 48 are installed on the input end of the signal processing unit 25 through switch circuits 41, 42 and while supply of the magnetic exciting current to the coil 13 is suspended, the switch circuits 41, 42 are connected in synchronization with a timing signal used as supply timing of the magnetic exciting current for on and off control and for supply of the simulated signal to the input end of the signal processing unit 25. Consequently, by this switching, the fluctuation of the DC-levels can practically be eliminated and automatic calibration during the flow measurement becomes available and high-accuracy flow measurement covering a long period of time becomes possible in a steady condition.

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 rheometer includes a detector that outputs a voltage signal proportional to the magnetic flux density in a measuring tube and a fluid flow rate, and a detector that amplifies the voltage signal detected by this detector to generate a flow 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 be kept for a long period of time to ensure stable operation. It is essential to maintain it.

By the way, the detector detects and outputs the flow rate using a pair of electrodes in the measuring tube, but normally, atoms that are components of the fluid, such as positive hydrogen ions, cause electrochemical action (cell action) on the electrode surface. As a result, DC and low frequency component noise is generated, which is superimposed on the flow rate output that should originally 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 outputs a flow rate S1 alSl taken from a pair of electrodes of the detector.
b (see factor 7) is a buffer amplifier 1.2 having an AC coupling means using capacitors Ca and Cb and a resistor 3.
4 to the signal processing unit 5, where it is converted into a flow rate signal and output.

On the other hand, the calibration means of the signal converter is the buffer amplifier 1.2.
Switch circuits 6a and 6b that selectively take in the detector flow rate output and a simulation signal for calibration are provided at the input terminals of the switch circuits 6a and 6b. Switch circuits 7a, 7 to turn off
DC power supply 9 via b and buffer amplifiers 8a and 8b.
The configuration is such that a simulated signal is supplied from the

[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, the signal A large fluctuation in the DC level occurs in the capacitor Ca5Cb at the input end of the converter, which temporarily causes the buffer amplifier 1.2 and signal processing section 5 to
There is a problem in that the amplifiers included in the system become saturated, making calibration and flow rate measurement impossible.

[Purpose of the invention]

The present invention has been made with attention to the above points, and is an electromagnetic system that supplies 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 generates a simulated signal through a switch circuit at the input end of the signal processing section. an electromagnetic flowmeter converter, in which the switch circuit is turned on in synchronization with the timing signal during a period when the excitation current is supplied to the excitation coil at a constant value, and the simulated signal is generated from the simulated signal generating means; be.

[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 measurement tube and the flow rate of the fluid,
This consists of a measuring tube 11 through which fluid flows, a pair of electrodes 12a and 12b installed opposite to the inner surface of the measuring tube 11, and an excitation coil 13 installed in the measuring tube 11.
For example, positive and negative constant currents are alternately supplied to this excitation coil 13 to generate a magnetic flux in the measurement tube, and a voltage signal that intersects with this magnetic flux and is induced in the fluid is transmitted to the pair of electrodes 12a, 12.
It is designed to be taken out with b.

Reference numeral 20 denotes a signal converter with 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 . 22 and the input end of the signal processing section 25 is connected via resistors 23 and 24. Also,
This signal converter includes a first excitation current supply means formed by connecting an excitation switch circuit 26 and a constant current source 27 in series, and a second excitation current supply means formed by connecting an excitation switch circuit 28 and a constant current source 29 in series. Excitation current supply means are provided, and both excitation supply means are connected in parallel to the excitation coil 13, and are connected to the switch circuit from the timing signal generation circuit 30 via an AND circuit 31, an inverter 32, an AND circuit 33, etc. 28 and 26 are provided with timing signals for alternately on/off control.

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 generating a simulated signal by controlling the switch circuits 41 and 42 on and off. In addition, the first AND circuit 46
1, an inverter 32, a second AND circuit 47, etc., and each AND circuit 46, 47 receives timing signals of mutually opposite levels from the timing signal generation circuit 3o to alternately turn on and off the switch circuits 42 and 41. It is meant to be controlled. 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 flowmeter 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 generating section 48 is inverted by the inverter 949 and becomes high level, and both AND circuits 31 and 33 are set to an operable state. At this time, when the timing signal generation circuit 30 outputs the timing signal S11 as shown in FIG. 2, the AND circuits 31, 32 alternately output high level signals 812, 813, and As a result, the switch circuits 28 and 26 are alternately turned on and off, and the excitation coil 13 is supplied with an excitation current S14 as shown in FIG.

As a result, a magnetic flux similar to the excited ta'R flow 814 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 a pair of electrodes Signals S15.316 as shown in the second factor are taken out from buffer amplifiers 21.12a and 12b.
22, the signal is impedance-converted with an amplification degree of 1 and is supplied to the signal processing section 25. Here, both signals 815.8
16 differential voltages are taken out in synchronization with the timing signal 811 and amplified. It is output as a quantity signal.

Next, the calibration operation will be explained with reference to FIG. In this case, the high level signal 82 is sent from the control signal generator 48.
0 is generated, which causes the output terminal of the inverter 48 to go low level, and furthermore, the output terminals of both AND circuits 31.33 to go low level, and the switch circuits 28.26
is off.

Therefore, due to the OFF state of the switch circuits 28 and 26, the excitation 11' IM current does not flow as shown at 823 in FIG. 3, and no magnetic flux is generated in the measuring tube. Since there is no magnetic flux inside the measuring tube 11, even if fluid flows through the measuring tube 11, a voltage signal proportional to the flow rate is not generated, and the electric current t! 112a, 12b
Only electrochemical noise 824, 325 is generated.

On the other hand, the AND circuits 46 and 47 are set to an operable state, and at this time, high-level signals are alternately input from the timing signal generation circuit 30 to the AND circuits 46 and 47 via the inverter 32 and directly, so that the switch circuit 41
．． 42 is alternately turned on and off as shown at 821 and S22 in FIG. 3, and a simulated signal is applied from the constant current source 43 to each input terminal of the signal processing section 25. That is, when the switch circuit 41 is in the on state, the constant current [43.

A current flows through the resistor 23 and a voltage drop occurs, but when it is turned off, no voltage drop occurs, so a signal 826 as shown in FIG. 3 appears, and the switch circuit 42 performs the same operation. Signals such as 827 appear, and these signals 826 and 827 are supplied to the signal processing section 25.

This signal 826.327 is the signal S15, S16 in FIG.
It can be seen that it is similar to , 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 relatively easily realized with high accuracy using a Zener diode, an operational amplifier, a resistor, etc. I can do it.

Therefore, the configuration of the embodiment as described above has the following effects. That is, usually a pair of electrodes 12
Electrochemical noise of about 100 times the flow rate signal is generated from the switch circuit 6a and 12b, but in conventional calibration means, the switch circuit 6a
, 6b causes an excessive change in the DC level on the input side of the capacitor Ca%cb, causing saturation of the amplifier and the like, making measurement and calibration impossible.

On the other hand, the signal converter calibration means in the present invention is
During calibration, only a reference voltage drop is applied from the electrochemical noise level, so there is almost no fluctuation in the DC level and the signal processing section 25 is never saturated. 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. A flow meter can be realized.

In addition, if automatic calibration becomes possible, there is no need to use high-precision components that affect the amplification degree in the signal processing section 25, etc., and the microprocessor itself can correct the signal conversion. The cost of the device 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. Exactly the same result can be obtained even if only the buffer amplifier 22 and the resistor 24 are connected. However, the signal processing section 25
In order to obtain a signal value equivalent to that obtained when applying a simulated signal to both input ends of the resistor 24 and the constant current source 43, 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. Normally, the resistors 51-54 and capacitors 55-58 are selected so as not to affect the amplification degree of the flow rate signal frequency, so there is no practical problem even though the buffer is outside the calibration loop. Further, the differential amplifier constituting the signal processing section 25 is an operational amplifier 251.
and a resistor 252, as shown in FIG. A simulated signal may be given to the end. In this case, a resistor 61 is connected to the other input terminal of the signal processing section 25.
shall be grounded via the Therefore, with such a configuration, the resistors constituting the signal processing section 25 can also be used as the voltage drop resistors 23 and 24. Further, in the above embodiment, the excitation current is set to zero when turned off, but a predetermined current may be supplied when turned off. 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, the simulated signal generating means is provided at the input end of the signal processing section via the switch circuit, and the switch circuit is excited during the period when the supply of excitation current to the excitation 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 fluctuations in the DC level can be prevented by switching. Therefore, it is possible to provide an electronic 1it18I quantity meter converter that can be automatically calibrated during flow rate measurement and can perform highly accurate flow rate measurement in a stable state over a long period of time.

[Brief explanation of drawings]

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 block diagram explaining the present invention in detail, FIG. 6 is a block diagram of a conventional device, and FIG. 7 is a waveform diagram explaining the operation of the conventional device. i o-...Detector, 12a, 12b-'! pole, 13・
... Excitation coil, 20 ... Signal converter, 25 ... Signal processing section, 30 ... Timing signal generation circuit, 41.
42... Switch circuit, 43... Constant current source, 45.
...Switch control circuit, 49...Control signal generation section. Figure 2 Figure 3 Figure 4 Figure 6 Figure 2b

Claims (6)

[Claims] (1) Excitation currents of two or more values with different polarities or current values are periodically supplied to the excitation coil, and the output of the flow rate detector taken out from the pair of electrodes is thereby passed through a buffer amplifier and a resistor to the signal processing unit. In the electromagnetic flowmeter converter that is introduced into the converter to obtain a flow rate signal, the excitation current is supplied to the excitation coil at a constant value, and a calibration control means outputs a switch changeover control signal in synchronization with a timing signal during the constant value period. , further comprising simulated signal generating means that turns on the switch circuit in response to the switch switching control signal obtained by the calibration control means and supplies a simulated signal of a predetermined level to the input terminal of the signal processing section. Electromagnetic flow meter converter. (2) The calibration control means maintains the supply of excitation current to the excitation coil at a constant value, and includes a control signal generating section that outputs an operable signal during the constant value period, and a control signal generating section that outputs an operable signal from the control signal generating section. 2. The electromagnetic flowmeter converter according to claim 1, further comprising a switch control circuit configured to be set to an operable state in response to the timing signal and output a switch changeover control signal in response to the timing signal. (3) The electromagnetic flowmeter 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 switch circuit is provided at one input end of the signal processing section.
Electromagnetic flowmeter converter described in section (6) The calibration control means calibrates the signal processing unit by continuously controlling the supply timing of the excitation current and the generation timing of the simulated signal at a ratio of N:1 (N is an integer). The electromagnetic flow meter converter according to item 1.