JP2880830B2 - Electromagnetic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic flow meter for measuring a flow rate of a conductive fluid.

[0002]

2. Description of the Related Art As one of electromagnetic flowmeters for measuring a flow rate of a conductive fluid or the like, the one shown in FIG. 6 is conventionally known.

The electromagnetic flowmeter shown in FIG. 1 comprises a measuring tube 102 through which a fluid 101 flows, a pair of electrodes 103a and 103b attached to the inner wall of the measuring tube 102, and an exciting coil 104 for applying a magnetic flux to the measuring tube 102. Detector 105, an excitation circuit 105 for supplying a current to an excitation coil 104 of the detector 105, and the electrodes 103 a and 103 a.
3b, which amplifies the electromotive force (voltage of a value proportional to the intensity of the magnetic flux and the average velocity of the fluid 101 flowing through the measuring tube 102) generated by the differential amplifier 3b. And a converter 108 comprising an arithmetic circuit 107 for processing to generate an output signal.

[0004] The fluid 10 flowing through the measuring tube 102 is
When measuring the flow rate in FIG.
An excitation signal (square wave current) shown in FIG. 7A is output to excite the excitation coil 104 to generate an alternating magnetic field in the measurement tube 102 as shown in FIG.
As shown in FIG. 7 (d), the electrodes 103a, 103a,
3b, the magnetic flux intensity due to the alternating magnetic field and the fluid 10
A voltage signal (flow signal) proportional to the average speed of 1 is generated and amplified by the differential amplifier circuit 106.

In parallel with this operation, the arithmetic circuit 107 is caused to perform a sampling operation by a sampling signal output from the excitation circuit 105 every time the square wave current is stabilized as shown in FIG. As shown in FIG. 7 (e), the flow rate signal output from the differential amplifier circuit 106 is fetched, and a calculation based on each flow rate signal fetched by this sampling operation is performed to make the signal cable 109 and the detector A noise caused by a change in magnetic flux traversing the loop circuit constituted by the loop 105 and a noise having a cycle longer than the cycle of the square wave current are removed to generate a flow rate signal shown in FIG. Let it.

[0006]

However, in the above-mentioned conventional electromagnetic flowmeter, the electrodes 103a, 103
Since the output impedance between “b” and “b” is inversely proportional to the conductivity of the fluid 101, the input impedance of the converter 108 is made extremely high so that the measurement result does not change even if the fluid conductivity changes.

For this reason, when the fluid 101 escapes from the measuring tube 102 of the detector 105, the input of the differential amplifier circuit 106 provided in the converter 108 becomes open and the influence of noise is reduced due to high impedance. This makes the value of the flow rate signal output from the arithmetic circuit 107 unstable, and when the trading of the fluid 101 is performed based on the integrated flow rate obtained by integrating the flow rate signal, the transaction is performed. In some cases, the reliability of the amount of the fluid 101 is lost.

Therefore, an electromagnetic flowmeter shown in FIG. 8 has been developed as an electromagnetic flowmeter that solves such a problem.

The electromagnetic flowmeter shown in FIG. 1 comprises a measuring tube 112 through which a fluid 111 flows, a pair of electrodes 113a and 113b attached to the inner wall of the measuring tube 112, and an exciting coil 114 for applying a magnetic flux to the measuring tube 112. Detector 115, an excitation circuit 116 for supplying a current to an excitation coil 114 of the detector 115, and the electrodes 113a and 113a.
A differential amplifier circuit 117 for amplifying the electromotive force (voltage of a value proportional to the intensity of the magnetic flux and the average velocity of the fluid 111 flowing through the measuring tube 112) generated at 3b, and connected to each input terminal of the differential amplifier circuit 117 Resistances 118 and 119 having a high value (a value that does not affect the conductivity of the fluid 111), and applying a reverse-polarity DC voltage to each of the input terminals via the resistances 118 and 119 (2) Two DC voltage sources 120,
121, a capacitor 122 for extracting an AC component of the flow signal output from the differential amplifier circuit 117, a signal processing circuit 123 for processing an AC component of the flow signal extracted by the capacitor 122 to generate an output signal, A resistor 124 that pulls down an input terminal of the signal processing circuit 123, a reference voltage source 125 that generates a reference voltage, and a value of a flow rate signal output from the differential amplifier circuit 117 is a reference voltage obtained by the reference voltage source 125. When the value is larger than the value, the comparator 12 which generates a fluid deflation detection signal
6. When the comparator 126 does not output the fluid loss detection signal, it takes in the flow rate signal output from the signal processing circuit 123 and outputs it, and the comparator 126 outputs the fluid loss detection signal. , And a converter 128 comprising an output circuit 127 for stopping signal output.

When a fluid 111 is present in the measuring tube 112, the conductivity of the fluid 111 and the resistance 1
18 and 119 to divide the DC voltage obtained by each of the DC voltage sources 120 and 121,
The above-described flow rate measuring operation is performed while preventing a DC voltage of “1” V or more from being generated between the electrodes 13b, thereby preventing the electrodes 113a and 113b from being polarized.

Then, the fluid 11 is supplied from the inside of the measuring tube 112.
1, the impedance between the electrodes 113a and 113b is increased, and as a result, each DC voltage source 120, 121
Differential amplifier circuit 117 by the DC voltage obtained by
DC voltage value input to each input terminal of
When the output voltage of the differential amplifier circuit 117 increases,
This is detected by the comparator 126 and the output circuit 1
The output of an erroneous flow signal from 27 is prohibited.

However, in such an electromagnetic flowmeter, it is necessary to increase the voltage value of the DC voltage sources 120 and 121 in order to increase the detection sensitivity of the detachment of the fluid 111. , 113b exceeds “1” V, a chemical action occurs between the electrodes 113a, 113b and the fluid 111, and the fluid 111 is electrolyzed to generate a gas such as hydrogen. There was a fear that it would.

The fluid 111 flowing through the measuring tube 112
Among them, there is a fluid to which a DC voltage of “10” V or more is applied. When measuring the flow rate of such a fluid 111, an extra voltage is applied between the electrodes 113 a and 113 b by the DC voltage applied to the fluid 111. When a voltage is generated and the DC component value of the fluid signal output from the differential amplifier circuit 117 becomes equal to or higher than the reference voltage, the comparator 126 malfunctions,
In some cases, the flow rate signal was not output from the output circuit 127.

In view of the above circumstances, the present invention makes it possible to reduce the influence of the conductivity of the fluid to be measured and the voltage applied to the fluid, and to prevent the occurrence of a chemical action at the electrode. It is possible to provide an electromagnetic flowmeter that can detect fluid leakage while preventing the output from becoming unstable even if fluid is released, thereby greatly improving reliability. The purpose is.

[0015]

In order to achieve the above object, an electromagnetic flowmeter according to the present invention generates an alternating magnetic field in a measuring tube and flows through the measuring tube to a pair of electrodes provided in the measuring tube. After generating a flow signal according to the flow rate of the fluid and performing a correction process by taking in the flow signal, in an electromagnetic flowmeter that outputs a flow signal obtained by the correction process, the excitation frequency of the excitation frequency is applied to each of the electrodes. An alternating voltage generating circuit for applying an alternating voltage having a frequency equal to one even number; sampling a flow signal output from each electrode a plurality of times within one cycle of the excitation frequency; A flow rate component extraction circuit for extracting and generating a flow rate signal corresponding to the flow rate component and outputting the flow rate signal output from each electrode within a half cycle of the alternating voltage; Ringing and calculating the average value, and when the average value difference of the alternating voltage for each half cycle becomes equal to or greater than a preset value, generates a fluid loss detection signal and outputs the output of the flow rate component extraction circuit. And a circuit for detecting a fluid loss that invalidates the fluid.

[0016]

In the above arrangement, the alternating voltage generating circuit applies an alternating voltage having a frequency equal to an even number of the exciting frequency to each electrode of the measuring tube, and the flow rate component extracting circuit applies the alternating voltage within one cycle of the exciting frequency. The flow signal output from each of the electrodes is sampled a plurality of times, a flow component in the flow signal is extracted, a flow signal corresponding to the flow component is generated and output, and in parallel with this operation. The flow signal output from each of the electrodes is sampled a plurality of times within a half cycle of the alternating voltage by the fluid loss detection circuit, an average value thereof is obtained, and an average value difference for each half cycle of the alternating voltage is determined in advance. When the value exceeds the set value, a fluid loss detection signal is generated and the output of the flow rate component extraction circuit is invalidated.

[0017]

FIG. 1 is a block diagram showing an embodiment of an electromagnetic flow meter according to the present invention.

The electromagnetic flow meter shown in FIG. 1 has a detector 1 and a converter 2, and generates an alternating magnetic field in a measuring tube 3 of the detector 1 by a square wave current output from the converter 2. While applying an alternating voltage having a frequency of "1/2" of the excitation frequency between the electrodes 4a and 4b, a flow signal corresponding to the flow rate of the fluid 5 flowing through the measuring tube 3 is output, and the converter 2
The flow rate component in the flow rate signal is extracted by a flow rate component extraction circuit 14 provided therein and output from an output circuit 16, and the alternating voltage component in the flow rate signal is extracted by a fluid loss detection circuit 15. When the value of the alternating voltage component becomes equal to or more than a preset value, this is detected and the output circuit 16 is inhibited from outputting a flow signal.

The detector 1 includes a measuring tube 3 through which a fluid 5 to be measured flows, an exciting coil 6 for generating an alternating magnetic field in the measuring tube 3, and a pair of electrodes 4a arranged in the measuring tube 6. , 4b, which takes in the square wave current output from the converter 2 via the exciting cable 7 and excites the exciting coil 6, whereby the same frequency as the frequency of the square wave current is introduced into the measuring tube 3. And an alternating voltage (flow signal) is generated between the electrodes 4a and 4b in accordance with the alternating magnetic field and the average flow velocity of the fluid 5 flowing through the measuring tube 3, and this is supplied via the signal cable 8. To the converter 2.

The converter 2 includes a timing generation circuit 10, an excitation circuit 11, an alternating voltage generation circuit 12, and an amplification circuit 13
And a flow component extraction circuit 14 and a fluid loss detection circuit 15
And an output circuit 16. A square wave current is generated by an excitation circuit 11 and supplied to the detector 1. An alternating voltage is generated by an alternating voltage generation circuit 12 and the square voltage is generated by the electrode 4a. The flow rate signal output from the electrodes 4a and 4b is taken in while being applied to the electrodes 4a and 4b, and the flow rate component in the flow rate signal is extracted by the flow rate component extraction circuit 14 and output from the output circuit 16; The alternating voltage component in the flow rate signal is extracted by the control circuit 15. When the value of the alternating voltage component becomes equal to or greater than a preset value, the detection is performed and the output circuit 16 detects the alternating voltage component.
Output of the flow rate signal from is prohibited.

The timing generation circuit 10 oscillates at a preset frequency as shown in FIG. 2 to generate an excitation signal shown in FIG. 3A and a sampling signal shown in FIG. 3B. 20 and a plus phase square wave signal shown in FIG. 3C and a minus phase square wave shown in FIG. A D-type flip-flop 21 for generating a signal and a positive-phase square wave signal output from the non-inverting output terminal of the D-type flip-flop 21 have a positive polarity and pass the sampling signal to An AND circuit 22 for outputting as a plus-phase sampling signal, and a minus-phase square outputted from the inverted output terminal of the D-type flip-flop 21 When the signal has a positive polarity, an AND circuit 23 which passes the sampling signal and outputs it as a minus phase sampling signal is provided, and oscillates at a preset frequency to generate an excitation signal. The excitation circuit 11 and the flow component extraction circuit 1
4 and a sampling signal is generated and supplied to the flow rate component extraction circuit 14. Along with this operation, a plus-phase square wave signal and a minus-phase square wave signal are generated, and these are generated by an alternating voltage generation circuit 1.
2, a plus-phase sampling signal and a minus-phase sampling signal are generated, and supplied to the fluid leakage detection circuit 15.

The excitation circuit 11 is provided with the timing generation circuit 1.
A square wave current shown in FIG. 3E is generated based on the excitation signal output from 0 and supplied to the detector 1 via the excitation cable 7.

The alternating voltage generating circuit 12 is connected to a DC voltage source 25 for generating a DC voltage serving as a reference. When the positive phase square wave signal output from the timing generating circuit 10 has a positive polarity, A switch 26 for passing the DC voltage obtained by the DC voltage source 25, and a high-value resistor 27 for applying the DC voltage passed through the switch 26 to one electrode 4a constituting the detector 1. A switch 28 that closes when the negative phase square wave signal output from the timing generation circuit 10 has a positive polarity and passes the DC voltage obtained by the DC voltage source 25; And a high-value resistor 29 for applying a DC voltage passed through to the other electrode 4b constituting the detector 1. When the plus-phase square wave signal output from the raw circuit 10 has a positive polarity, one switch 26 is closed to take in the DC voltage obtained by the DC voltage source 25, and This DC voltage is applied to one electrode 4a, and when the negative phase square wave signal output from the timing generation circuit 10 is positive, the other switch 28 is closed and the DC voltage source 25 The DC voltage obtained by the above is taken in, and this DC voltage is applied to the other electrode 4b via the resistor 29.

An amplifier circuit 13 amplifies a flow signal output from each of the electrodes 4a and 4b via the signal cable 8, and each input terminal of the differential amplifier circuit 30 and a ground point. And two high-valued resistors 31 and 32 interposed between the electrodes 4a and 4b of the detector 1 while the electrodes 4a and 4b of the detector 1 are grounded by the resistors 31 and 32, respectively. The output voltage is differentially amplified to generate a flow rate signal, which is used as a flow rate component extraction circuit 14,
The fluid is supplied to the detection circuit 15.

In this case, since the polarity of the DC voltage output from the alternating voltage generating circuit 12 is switched at a frequency of "1/2" of the square wave current applied to the exciting coil 6 of the detector 1, The flow signal shown in FIG. 3F is output from the amplifier circuit 13 and supplied to the flow component extraction circuit 14 and the fluid loss detection circuit 15.

When the polarity of the excitation signal output from the timing generation circuit 10 is positive, the flow component extraction circuit 14 detects the amplification signal based on the sampling signal output twice from the timing generation circuit 10. 3 (g) is extracted by sampling the flow rate signal output from the controller, and a difference between these signals is calculated to generate a flow rate signal from which the DC component contained in the flow rate signal is removed. When the polarity of the excitation signal output from the timing generation circuit 10 is negative, the flow rate signal output from the amplification circuit 13 based on the sampling signal output twice from the timing generation circuit 10 is output. A signal is extracted by sampling, and a difference between these signals is calculated to remove a DC component included in the flow rate signal. Generates a signal, hereinafter supplies the flow rate signal obtained by repeating this operation (signal shown by hatching) to the output circuit 16.

As shown in FIG. 2, the fluid leakage detection circuit 15 includes two resistors 35 and 36, one end of which is connected to the output terminal of the amplification circuit 13, and the timing generation circuit 10.
When a plus-phase sampling signal is output from the, the flow rate signal output from the amplifying circuit 13 is passed through one of the resistors 35 through the closed state, and FIG.
Switch 37 for generating flow pulse signal shown in (h)
A capacitor 38 for averaging the flow rate pulse signal obtained by the switch 37 to extract a DC component included in the flow rate signal and generating a DC voltage value on the plus phase side indicated by a dotted line; Generating circuit 10
When the negative phase sampling signal is output from the, the flow rate signal output from the amplifying circuit 13 is passed through the other resistor 36 through the closed state and the flow rate signal shown in FIG.
Switch 39 for generating flow pulse signal shown in (i)
And a capacitor 40 for averaging the flow rate pulse signal obtained by the switch 39 to extract a DC component included in the flow rate signal and generating a DC voltage value on the minus phase side indicated by a dotted line; Each capacitor 3
A differential amplifier circuit 41 that extracts the difference between the DC voltage value on the plus phase side and the DC voltage value on the minus phase side obtained by steps 8 and 40 and outputs a DC voltage value signal as shown in FIG. And

Further, the fluid leakage detection circuit 15 compares a reference voltage source 42 for generating a reference voltage with a reference voltage obtained by the reference voltage source 42 and a signal output from the differential amplifier circuit 41. And a comparator 43 for generating a fluid loss detection signal when the value of the signal output from the differential amplifier circuit 41 is higher than the reference voltage.

Each time a plus-phase sampling signal is output from the timing generation circuit 10, one switch 37 is closed to sample the flow signal output from the amplification circuit 13 and one capacitor 38, the flow rate pulse signal obtained by the sampling operation is averaged to generate a DC voltage value on the plus phase side.
Each time a minus phase sampling signal is output from 0, the other switch 39 is closed to sample the flow rate signal output from the amplifier circuit 13 and obtain the signal by the sampling operation by the other capacitor 40. The flow pulse signal is averaged to generate a negative-phase DC voltage value. In parallel with this operation, the difference between the positive-phase DC voltage value and the negative-phase DC voltage value is output by the differential amplifier circuit 41. When the difference exceeds the reference voltage, the comparator 43 detects the difference to generate a fluid loss detection signal and supplies it to the output circuit 16.

The output circuit 16 is provided with the fluid bleed detection circuit 15.
When the fluid loss detection signal is not output from the above, the flow rate signal output from the flow rate component extraction circuit 14 is fetched and output, and when the fluid loss detection signal is output from the fluid loss detection circuit 14, Stop signal output.

As described above, in this embodiment, an alternating magnetic field is generated in the measuring tube 3 of the detector 1 by the square-wave current output from the converter 2 and "1/1" of the excitation frequency is applied between the electrodes 4a and 4b. An alternating voltage having a frequency of 2 ″ is applied to output a flow signal corresponding to the flow rate of the fluid 5 flowing through the measurement tube 3, and this is output by the flow component extraction circuit 14 provided in the converter 1. The flow rate component in the signal is extracted and output from the output circuit 16, and the alternating voltage component in the flow rate signal is extracted by the fluid loss detection circuit 15, and the value of the alternating voltage component is equal to or greater than a preset value. Is detected, the output circuit 1
Since the output of the flow rate signal from the fluid 6 is prohibited, the influence of the conductivity of the fluid 5 to be measured and the voltage applied to the fluid 5 can be reduced. Fluid loss can be detected while preventing chemical action from occurring at the electrodes 4a and 4b,
Further, the output can be prevented from becoming unstable even if the fluid 5 comes out, so that the reliability can be greatly improved.

In the above-described embodiment, the alternating voltage generating circuit 12 constituted by the DC voltage source 25, the two switches 26 and 28, and the two resistors 27 and 29
Is used, but the resistance 3
1. Alternating voltage generation circuit 12a shown in FIG.
Alternatively, the alternating voltage generation circuit 12b shown in FIG. 5 may be used.

In this case, the alternating voltage generation circuit 12 shown in FIG.
In a, when the plus-phase square wave signal output from the timing generation circuit 10 has a positive polarity, the DC voltage output from the DC voltage source 51 is selected by one of the switches 54, and this is connected to the capacitor 56 and the resistance. 5
5 are sequentially applied to one electrode 4a of the detector 1 via the other electrode 4b, and the other switch 50 selects the ground point to select the other electrode 4b of the detector 1.
Is sequentially grounded through a resistor 53, a capacitor 52, and a switch 50, and when the negative phase square wave signal output from the timing generation circuit 10 has a positive polarity, the other switch 50
Is applied to the other electrode 4b constituting the detector 1 via the capacitor 52 and the resistor 53 in this order, and the one switch 54
One of the electrodes 4a constituting the detector 1 is selected by a resistor 55, a capacitor 56, a switch 5
4 are successively grounded, and thereafter, this operation is repeated, and a DC voltage having a frequency of "1/2" of the square wave current is applied to each of the electrodes 4a and 4b.

The alternating voltage generation circuit 12b shown in FIG.
When the plus-phase square wave signal output from the timing generation circuit 10 has a positive polarity, the DC positive voltage output from one DC voltage source 61 is selected by one switch 60, and this is connected to a resistor 62. Is applied to one electrode 4a constituting the detector 1 via the other switch 57, and is supplied to the other DC voltage source 58 by the other switch 57.
Is selected, and this is connected to the resistor 59.
Is applied to the other electrode 4b of the detector 1 through the negative electrode, and the negative phase square wave signal output from the timing generation circuit 10 has a positive polarity.
One switch 60 selects a DC negative voltage output from the other DC voltage source 58, and this voltage is applied to one electrode 4 a of the detector 1 via a resistor 62, and one switch 4 The positive DC voltage output from the DC voltage source 61 is selected and applied to the other electrode 4b constituting the detector 1 via the resistor 59. Thereafter, the operation is repeated, and each of the electrodes 4a,
A DC voltage having a frequency of "1/2" of the square wave current is applied to 4b.

[0035]

As described above, according to the present invention, it is possible to reduce the influence of the conductivity of the fluid to be measured and the voltage applied to the fluid,
Fluid leakage can be detected while preventing chemical action at the electrodes, and the output can be prevented from becoming unstable even if the fluid escapes, thereby greatly improving reliability. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an electromagnetic flow meter according to the present invention.

FIG. 2 is a circuit diagram showing a detailed circuit example of a timing generation circuit and a fluid loss detection circuit shown in FIG.

FIG. 3 is a waveform chart showing an operation example of the electromagnetic flow meter shown in FIG.

FIG. 4 is a circuit diagram showing an example of another alternating voltage generation circuit used in the electromagnetic flow meter according to the present invention.

FIG. 5 is a circuit diagram showing an example of another alternating voltage generation circuit used in the electromagnetic flow meter according to the present invention.

FIG. 6 is a block diagram showing an example of a conventionally known electromagnetic flow meter.

FIG. 7 is a waveform chart showing an operation example of the electromagnetic flow meter shown in FIG.

FIG. 8 is a block diagram showing another example of a conventionally known electromagnetic flow meter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detector 2 Converter 3 Measuring tube 4a, 4b Electrode 5 Fluid 6 Excitation coil 11 Excitation circuit 12 Alternating voltage generation circuit 13 Amplification circuit 14 Flow rate component extraction circuit 15 Fluid loss detection circuit 16 Output circuit

Claims (1)

(57) [Claims] 1. An alternating magnetic field is generated in a measuring tube to generate a flow signal corresponding to a flow rate of a fluid flowing through the measuring tube on a pair of electrodes provided in the measuring tube, and the flow signal is taken in and corrected. An electromagnetic flowmeter that outputs a flow signal obtained by the correction processing after performing the processing, wherein an alternating voltage generation circuit that applies an alternating voltage having a frequency that is an even-numbered excitation frequency to each of the electrodes; The flow rate signal output from each electrode is sampled a plurality of times within one cycle of the excitation frequency to extract a flow rate component in the flow rate signal, and a flow rate signal corresponding to the flow rate component is generated and output. A circuit, and sampling the flow rate signal output from each electrode a plurality of times within a half cycle of the alternating voltage to obtain an average value thereof, and for each half cycle of the alternating voltage, A fluid loss detection circuit that generates a fluid loss detection signal and invalidates the output of the flow rate component extraction circuit when the average value difference is equal to or greater than a preset value. Electromagnetic flow meter.