JP2003028684A - Electromagnetic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the adhesion of an insulator or the like on a detection electrode in a detector and to detect the increase in contact resistance. SOLUTION: The electromagnetic flowmeter that has a measurement pipe where fluid to be measured flows for detecting failure in the detector comprises an adhesion diagnosis circuit for measuring the resistance of an electrode in contact with the fluid, an electrode lead for connecting the electrode that is mounted to the measurement pipe and an adhesion diagnosis circuit, and a battery for driving the adhesion diagnosis circuit.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electromagnetic flow meter for detecting abnormality of a detector.

[0002]

2. Description of the Related Art As an electromagnetic flow meter for measuring a flow rate based on a signal electromotive force obtained from a fluid by applying a magnetic field to the fluid, one having a structure as shown in FIG. 4 is known. In this example, there is no fluid, that is, empty detection is performed. The electromagnetic flowmeter of this example includes a detector 100 that generates a predetermined magnetic field to detect a signal electromotive force generated in a fluid,
A converter 1 that processes a signal electromotive force from the detector 100 to calculate a flow rate and converts the signal into a predetermined process control signal for output.
01 and 01.

The detector 100 includes a coil 200 for generating a predetermined magnetic field, a measuring tube 300 through which a fluid to be measured flows,
The detection electrodes 400a and 400b, which are arranged to face the inner surface of the measurement tube 300 and come into contact with the fluid, and the measurement tube 3
Fluid in 00 has the same potential as the measuring tube 300 (ground potential)
A common electrode (earth ring) 500 for supplying the electric field is provided.

In the converter 101, a power supply section 110 for generating a predetermined power supply voltage from a loop current supplied from a process control device (not shown), an excitation section 120 for outputting an excitation current of a predetermined frequency to a coil 200, a buffer 130, The output of the AC amplification unit 140 that differentially amplifies the signal electromotive force obtained from the detection electrodes 400a and 400b, the high pass filter 150 that attenuates low frequency components such as fluid noise among the outputs of the AC amplification unit 140, and the output of the high pass filter 150. A control unit 170 and a control unit 170 that sample the flow rate from the outputs of the A / D conversion unit 160 and the A / D conversion unit 160 that sample at a predetermined interval and convert it into digital information, and control each unit in the converter 101. Output interface unit 1 that outputs a predetermined process control signal based on the flow rate information from the It is equipped with a 0. Then, the AC amplifier 140, the high-pass filter 150, the A / D converter 16
0 and the controller 170 constitute a flow rate detection system.

Ra and Rb are detection electrodes 400a and 400b.
Is a minute resistor for sky detection, and the sky detection unit 1
90 is a detection electrode 400 obtained via the buffer 130.
Comparing the potentials of a and 400b with the reference voltages Va and Vb provided for the detection electrodes 400a and 400b, the comparators 190a and 190b are provided, and the detection electrodes 400 and
a and 400b are corresponding reference voltages Va,
When Vb is exceeded, an empty detection signal is output to the control unit 170. In addition, + V is a positive power supply voltage higher than ground potential, -V
Is a negative power supply voltage lower than the ground potential, and the reference voltages Va and Vb are set to predetermined values between the power supply voltages + V and −V and the ground potential, respectively.

Next, in such an electromagnetic flow meter, a method for detecting the sky when there is no fluid will be described. Figure 5
It is explanatory drawing which shows the circuit part regarding empty detection, (a) is explanatory drawing which shows the circuit part regarding empty detection among the electromagnetic flowmeters shown in FIG. 4, (b) is explanatory drawing which shows the detection electrode 400a side. In FIG. 5, Za and Zb are fluid resistances generated between the detection electrodes 400a and 400b and the common electrode 500 by the fluid, and Ia is a power supply voltage + V to a resistance R.
a, detection electrode 400a, fluid resistance Za, and common electrode 5
A current Ib flowing to the ground potential via 00, Ib is from the ground potential to the common electrode 500, the fluid resistance Rb, and the detection electrode 400b.
And a current flowing to the power supply voltage -V via the resistor Rb.

As shown in FIG. 5B, a minute current Ia is constantly supplied to the fluid resistance Za from the power supply voltage + V via the resistance Ra, and the resistance Ra and the fluid resistance Za are By comparing the point potential, that is, the potential of the detection electrode 400a and the reference voltage Va with the comparator 190a, the change in the current Ia due to the change in the fluid resistance Za is detected.

In this case, when the fluid does not come into contact with the detection electrode 400a due to the decrease in the flow rate and the fluid resistance Za increases or becomes infinite, and the potential of the detection electrode 400a rises above the reference voltage Va, Comparator 190
The output of a is inverted, and the fluid in the measuring tube 300, particularly the fluid on the detection electrode 400a and the fluid on the common electrode 500 side, is detected to be in an empty state, and the output of the invalidity determination of the flow rate detected immediately before or the empty detection alarm is output. Used for. In the detection electrode 400b to which the power supply voltage −V is constantly supplied, the empty state is detected when the midpoint potential, that is, the potential of the detection electrode 400b drops below the reference voltage Vb, contrary to the above.

[0009]

Therefore, in such a conventional electromagnetic flowmeter, the detection electrode 400 is used to detect the sky.
Since a current is constantly supplied to the a and 400b from the power supply voltages + V and -V, respectively, the fluid resistances Za and Z
The electric charge is moved in one direction via b, and due to the electric charge, an electrochemical reaction occurs at the interface between the detection electrodes 400a and 400b and the fluid due to the relationship between the material of the detection electrodes 400a and 400b and the fluid. Electrode 400a or 400b
In some cases, an insulator may adhere to the liquid contact surface of the device, and if the contact resistance between the insulator and the fluid increases, the signal electromotive force indicating the original flow rate cannot be accurately detected by the detection electrodes 400a and 400b. There is a problem that becomes.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an electromagnetic flowmeter for detecting that an insulator or the like is attached to a detection electrode in a detector to increase the contact resistance. To aim.

[0011]

The present invention for achieving the above object is as follows. (1) In an electromagnetic flowmeter that includes a measuring tube through which a fluid to be measured flows, and which is attached to the measuring tube, an adhesion diagnostic circuit that measures the resistance of an electrode that contacts the fluid. An electromagnetic flowmeter, comprising: an electrode lead wire for connecting the electrode and the adhesion diagnosis circuit; and a battery for driving the adhesion diagnosis circuit. (2) The electromagnetic flowmeter according to (1), wherein the battery is a solar cell. (3) The electromagnetic flowmeter according to (1) or (2), characterized in that an indicator capable of being externally monitored is provided in the adhesion diagnosis circuit. (4) The electromagnetic flowmeter according to any one of (1), (2) or (3), wherein the adhesion diagnosis circuit is provided with a wireless communication circuit for transmitting a signal to the outside.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a partially enlarged view of the electromagnetic flowmeter of the present invention. A lining 1 made of Teflon (registered trademark), urethane, or the like is incorporated along the wall of the non-magnetic measuring tube 3 through which the fluid to be measured flows. The lining 1 is provided with a hole 1a, and the electrode 2 having a coil is incorporated in the hole 1a. Then, a part of the measuring pipe 3 meshes with the recessed portion 1b provided in the central portion of the lining 1. The inner wall of the measuring tube 3 has a shape that engages with the electrode cap 4, and the inner wall of the measuring tube 3 and the outer wall of the electrode cap 4 engage with each other. The electrode cap 4 covers the electrode 2.

Above the electrode 2, a substrate 9 and a glass 8 for an adhesion diagnosis circuit for detecting adhesion of an insulator are arranged. Electrode 2
And the substrate 9 of the adhesion diagnosis circuit are connected by an electrode lead wire 10, and the electrode 2 to the signal line 5 are connected to the detection circuit of the converter. A ground wire 11 connects between the substrate 9 of the adhesion diagnostic circuit and the end of the housing 6. In addition, the ends of the substrate 9 and the glass 8 of the adhesion diagnosis circuit are joined by the joining member 15
Glued by. A housing 6 is provided on the side of the substrate 9 of the adhesion diagnosis circuit, and a maintenance cap 7 is engaged with the outer wall of the housing 6. The upper portion of the maintenance cap 7 contacts the surface of the glass 8. The electromagnetic flowmeter of the present embodiment is
A feature of the present invention is that the maintenance cap 7 is provided with an adhesion diagnosis circuit (9) as compared with a normal electrode exchange type electromagnetic flowmeter.

2 and 3 show the adhesion diagnosis circuit on the substrate 9 of the adhesion diagnosis circuit. As shown in FIGS. 2 and 3, this circuit is composed of an electrode 2, a constant current circuit 13, a buffer 16 and a voltmeter 12 for monitoring the voltage appearing at the electrode 2. This adhesion diagnosis circuit is battery-powered, and a solar cell can be used for this battery. The voltage V appearing on the electrode 2 by the current Io given from the constant current circuit 13 is represented by the following formula (1), where Rf is the resistance between the electrode and the ground. V = Io × Rf (1)

As an example of the constant current circuit 13, although the one using the direct current Vdc is shown in FIGS. 2 and 3, the alternating current Vdc is used.
The constant current circuit 13 may be configured to use ac.

Here, if the electrode is attached, the value of Rf becomes large, so an alarm is issued when the value of V becomes large to some extent. Furthermore, an indicator such as the voltmeter 12 is provided so that the state of the electrode resistance can be known from outside the detector.

For information transmission to a person who performs maintenance, a voltmeter 12 having the indicator shown in FIGS. 2 and 3 is used.
Alternatively, the wireless communication circuit 14 may be installed to wirelessly transmit a signal to the outside.

As described above, according to the present invention, the adhesion diagnostic circuit for measuring the resistance of the electrode in contact with the fluid to be measured and the electrode attached to the measuring tube through which the fluid is flowed and the adhesion diagnostic circuit are connected. Since it is provided with an electrode lead-out wire for doing so, it is possible to determine whether or not the insulator has adhered to the electrode by the adhesion diagnosis circuit, so that it is possible to easily detect abnormality of the detector including the electrode.

Further, since the detector can be independently driven by the battery, it is possible to perform abnormality diagnosis of the electromagnetic flow meter currently used in the field.

If the battery is a solar cell, it is possible to improve the efficiency of the work without replacing the battery.

Further, by providing an indicator which can be monitored from the outside of the electromagnetic flow meter in the adhesion diagnosis circuit, it becomes possible to easily grasp the condition of the electrode resistance visually from the outside.

[0023]

According to the present invention, in order to solve the problem that the measurement becomes impossible when the insulator adheres to the electrode, a constant current circuit is provided in the electrode section and the electrode resistance is measured to detect the abnormality of the detector. Can be detected. Then, it is possible to realize an electromagnetic flow meter in which the detector can be replaced or maintained before the detector becomes abnormal. In addition, by changing the polarity of the current value of the constant current source or increasing the value, it is possible to obtain the effect of removing insulating deposits.

[Brief description of drawings]

FIG. 1 is a partially enlarged view of an electromagnetic flow meter of the present invention.

FIG. 2 is a diagram showing an example of a circuit for performing adhesion diagnosis in the electromagnetic flow meter of the present invention.

FIG. 3 is a diagram showing another circuit example for performing adhesion diagnosis in the electromagnetic flow meter of the present invention.

FIG. 4 is a block diagram of a conventional electromagnetic flow meter.

FIG. 5 is an explanatory diagram showing a circuit portion related to sky detection,
(A) is explanatory drawing which shows the circuit part regarding empty detection,
(B) is an explanatory view showing the detection electrode 400a side.

[Explanation of symbols]

1 lining 1a hole 2 electrodes 3 measuring tubes 4 electrode cap 5 signal lines 6 housing 7 Maintenance cap 8 glass 9 Adhesion diagnosis circuit board 10 Electrode lead wire 11 ground wire 12 Voltmeter 13 constant current circuit 14 Wireless communication circuit

Claims (4)

[Claims] 1. An adhesion flow diagnostic circuit for measuring the resistance of an electrode in contact with a fluid in an electromagnetic flowmeter for detecting an abnormality of a detector, comprising: a measuring tube through which a fluid to be measured flows.
An electromagnetic flowmeter comprising: an electrode lead wire for connecting an electrode attached to the measurement tube and an adhesion diagnosis circuit; and a battery for driving the adhesion diagnosis circuit. 2. The electromagnetic flowmeter according to claim 1, wherein the battery is a solar cell. 3. The electromagnetic flow meter according to claim 1, wherein the adhesion diagnosis circuit is provided with an indicator that can be monitored from the outside. 4. The electromagnetic flowmeter according to claim 1, wherein the adhesion diagnosis circuit is provided with a wireless communication circuit for transmitting a signal to the outside.