JP2003106879A - Electromagnetic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diagnose the state of the insulation deterioration of a coil section so as to detect whether or not flow rate measurement is performed normally. SOLUTION: An electromagnetic flowmeter performs the flow rate measurement by detecting a voltage proportional to the flow velocity of a conductive fluid which becomes an object to be measured by means of an electrode in a detector, by generating a magnetic field in the detector by supplying a current from an exciting circuit to an exciting coil provided in the detector. The flowmeter is provided with a circuit which measures the insulation resistance between the exciting coil and a grounding electrode.

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 having a function of diagnosing a state of insulation deterioration of a coil by measuring insulation deterioration of a coil portion.

[0002]

2. Description of the Related Art In a general electromagnetic flow meter, the flow velocity in a measuring tube is measured from the voltage detected by an electrode in a detector. Specifically, a magnetic field is generated in the detector by supplying a current from the exciting circuit to the exciting coil in the detector. At this time, when the conductive fluid flows in the detector, a voltage is generated as a signal detected from an electrode arranged perpendicular to the coil that generates the magnetic field. This causes a voltage proportional to the magnetic flux density and the flow velocity in the measuring tube through which the conductive fluid to be measured flows.

[0003]

However, in a general electromagnetic flowmeter, when the (conductive) fluid enters from the seal portion in the detector, the resistance between the coils decreases.
Resistance between grounds (metal measuring tube) decreases. Further, when the fluid enters the coil portion, a resistance having a resistance value of several to several tens MΩ is connected in parallel between the coil terminals and between the coil and the ground (metal measuring tube). When this resistance is measured, the coil resistance between the coils is several tens to several hundreds Ω, and therefore it cannot be detected when the resistance connected in parallel has a resistance value of several to several tens MΩ. If this state is left undetected, a coil short circuit will eventually occur, and a magnetic field cannot be generated in the measuring tube, making flow rate measurement impossible.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electromagnetic flow meter having a function of diagnosing a state of insulation deterioration of a coil in order to enable normal flow rate measurement. And

[0005]

According to the present invention for achieving the above object, a conductive material to be measured by supplying a current from an exciting circuit to an exciting coil in a detector to generate a magnetic field in the detector. An electromagnetic flowmeter for measuring a flow rate by detecting a voltage proportional to a flow velocity of a fluid by an electrode in the detector, comprising a circuit for measuring an insulation resistance between the exciting coil and an earth electrode. It is a characteristic electromagnetic flow meter.

Therefore, a circuit for measuring insulation deterioration of the insulation resistance (coil part) between the exciting coil and the ground electrode is provided, and it becomes possible to diagnose the state of insulation deterioration of the coil part. It is possible to detect whether the flow rate is measured normally.

Further, according to the present invention, the exciting circuit and the ground electrode are insulated, a voltage is applied between the exciting coil and the ground electrode, and the voltage flows between the exciting coil and the ground electrode. The electromagnetic flowmeter according to (1), further comprising a circuit for measuring an insulation resistance between the exciting coil and the ground electrode from a current.

Therefore, a voltage is applied between the insulated exciting circuit and the earth electrode, and the insulation resistance between the exciting coil and the earth electrode is measured from the current flowing therethrough, so that the decrease in the insulation of the exciting coil is detected online. It becomes possible to do.

In addition to the flow rate measuring circuit for measuring the flow rate, the present invention comprises an insulation resistance detecting circuit for diagnosing insulation resistance deterioration, and switching means for switching between the flow rate measuring circuit and the insulation resistance detecting circuit. The electromagnetic flowmeter according to (1), further comprising:

Therefore, in addition to the flow rate measuring circuit (excitation circuit) of the electromagnetic flow meter, an insulation resistance detecting circuit for diagnosing insulation resistance deterioration, and a switching means for switching the flow rate measuring circuit and the insulation resistance detecting circuit. When the insulation resistance is measured, the connection with the flow rate measuring circuit is cut by the switching means (for example, a relay), and the exciting coil and the insulation resistance detection circuit are connected by the switching means (for example, a relay). Further, when measuring the flow rate, the connection with the insulation resistance detection circuit is cut by a switching means (for example, a relay), and the exciting coil and the flow rate measurement circuit are connected by a switching means (for example, a relay).

Further, according to the present invention, the insulation resistance detecting circuit measures an insulation resistance between the exciting coil electrically insulated from the flow rate measuring circuit by the switching means and the ground electrode. The electromagnetic flowmeter according to (3), which is characterized.

Therefore, by applying a voltage between the exciting coil and the ground electrode and measuring the insulation resistance between the exciting coil and the ground electrode from the current flowing therethrough, the exciting coil and the flow rate measuring circuit can be used even in the offline case. Even if and are not insulated, it is possible to detect the insulation deterioration of the coil part.

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

The flow rate measurement of the electromagnetic flow meter according to the embodiment of the present invention described below is performed as follows. Specifically, a magnetic field is generated in the detector 6 by supplying a current from the exciting circuit 10 to the exciting coil 8 in the detector 6. At this time, when a conductive fluid flows in the detector 6, a magnetic flux in a measuring tube (not shown) is detected as a signal detected from an electrode (not shown) arranged perpendicular to the exciting coil 8 for generating the magnetic field. A voltage proportional to the density and flow velocity is generated. The electromagnetic flowmeter measures the flow velocity in the measuring tube from the voltage detected from the electrode.

FIG. 1 is a circuit block diagram in which the present invention is applied to a two-wire type electromagnetic flow meter. DC power supply (external power supply) 11
A current output circuit 9, an excitation circuit 10, a digital circuit (CPU) 7 and a SW control circuit 5 are connected in parallel by a power line 1 and a common line 2. Also,
The SW control circuit 5 forms a part of the DC-DC conversion circuit 12. The insulation type DC-DC converter 12 functions as a power source for the analog amplifier circuit 13 and the A / D converter 15. The current output circuit 9 has a function of outputting an output current detection signal, and has a digital circuit (CPU).
A timing signal / excitation current detection signal is input / output between 7 and the excitation circuit 10. Further, a PWM signal is input / output between the current output circuit 9 and the digital circuit (CPU).

Digital circuit (CPU) 7 and insulating circuit 17
Input / output of A / D converted signals is performed between
The A / D converter 15 is connected to the insulating circuit 17,
Further, they are also connected by a power supply line 3 and a common line 4. Also, the common line 4 and the excitation circuit 10
Is insulated. The power supply line 2 and the common line 2 are connected to the analog amplifier circuit 13.
Each buffer in the analog amplifier circuit 13 is connected to the detector 6. The digital circuit (CPU) 7 is connected to the insulating circuit 19, and the coil abnormality detection signal is input / output between the digital circuit (CPU) 7 and the insulating circuit 19. Further, the isolation circuit 19 includes an A / D converter 2
1 is connected.

Next, the state of processing of the signal detected in the detector 6 will be described. A signal detected from an electrode (not shown) is buffered / differentially amplified by the buffer 13a and the differential amplifier 13b in the analog amplifier circuit 13 shown in FIG. 1, and converted into a digital signal by the A / D converter 15. Since the reference potential of the DC power source (same as the excitation circuit reference) 11 and the reference potential of the detector 6 side are not the same, this digital signal is transmitted to the digital circuit (CPU) 7 that performs arithmetic processing through the insulating circuit 17. To be done.

FIG. 2 is a circuit block diagram in which the present invention is applied to a 4-wire electromagnetic flowmeter. The power supply 25 is provided with a power supply control circuit 27. An insulation circuit 29 is connected to the current output circuit 28, and the insulation circuit 29 is connected to the CPU 31.
Is connected to input and output a current output signal. Further, the CPU 31 is connected to the analog amplifier circuit 35 and the A / D converter 32, and processes the signal from the electrode in the detector 22. Further, the CPU 31 is connected to the insulation circuit 33 and the excitation circuit 30, and inputs and outputs an excitation control signal with the insulation circuit 33. Further CPU3
Reference numeral 1 is connected to the A / D converter 36 to input / output a coil abnormality detection signal to / from the A / D converter 36.

The status of processing of the signals detected from the electrodes in the detector 22 is shown. The signal detected from the electrode in the detector 22 is buffered / differentially amplified by the buffer 35a and the differential amplifier 35b in the analog amplifier circuit 35 shown in FIG. 2, and converted into a digital signal by the A / D converter 32. After that, the data is transmitted to the CPU 31. The CPU 32 calculates the flow rate based on the transmitted data. Then, the voltage supplied from the power supply 25 is supplied to the current output circuit 28, the flow rate signal measurement circuit (CPU 32) and the excitation circuit 30 in an insulated state through the power supply control circuit 27. Here, the excitation circuit 30 and the common line 20 (earth electrode of the detector) are insulated as in FIG.

FIG. 3 shows an example of the structure of a general excitation circuit used in the electromagnetic flowmeter shown in FIGS. 1 and 2. This exciting circuit includes a current direction switching circuit 40 and a constant current control circuit 41.
Composed of. The current direction switching circuit 40 controls the direction of the current flowing in the exciting coil 43 by turning on / off the transistors Q1 to Q4. This timing signal is given to the gates of Q1 to Q4 through T1 to T4 generated by the digital circuit through the insulating circuit. And
The timing is as shown in Table 1 below.

[0020]

[Table 1]

In FIG. 1, the current output circuit 9 and the excitation circuit 10 are shown.
Since the circuit reference of the constant current control circuit 41 is the same,
The signal proportional to the exciting current detected from A / D is converted, and the signal can be transmitted to the digital circuit (CPU) 7 which performs the arithmetic processing without insulation. Thereby, the flow rate signal can be easily divided by the exciting current. When the excitation circuit shown in FIG. 3 is applied to FIG. 2, a constant DC current is applied by applying a reference DC voltage to the PWM signal in FIG.

Here, the circuit for measuring the coil insulation resistance is common to FIGS. 1 and 2, and an AC or DC voltage Echk is applied to both ends 43 of the exciting coil via the resistor R1.
Connect to. Here, the value of R1 is adjusted to the order of the insulation resistance Rz to be measured. For example, when it is desired to measure 10 MΩ as the insulation resistance Rz between the coil and the ground electrode, R1 is set to 10 MΩ. Then, the following (1)
The formula holds.

[0023] E1 = Rz / (R1 + Rz) × Echk (1)

In a normal state, the coil and the ground electrode are insulated from each other, so that E1 = Echk. Here, when Rz = 10 MΩ between the coil and the ground electrode, E1 = Echk
/ 2. In this way, by monitoring E1, it is possible to detect the insulation deterioration due to the fluid ingress of the coil.

Next, an exciting circuit and an insulation resistance measuring circuit are connected in parallel to the exciting coil and switched by a switch such as a relay to switch the exciting circuit and the ground electrode even if they are insulated from each other. An embodiment will be described in which the insulation degradation of the coil portion is measured even when the electrodes are not insulated. FIG. 4 shows an embodiment in which the excitation circuit 45 and the insulation resistance measuring circuit 49 are connected in parallel and the insulation degradation of the coil portion is measured by switching with a SW such as a relay.

FIG. 4 shows an insulation resistance detecting circuit 49 which is a circuit for measuring the insulation resistance between the exciting coil and the earth (pipe, flange, etc.) in the detector. In the present embodiment, in addition to the flow rate measurement circuit (excitation circuit 45) of the conventional electromagnetic flow meter, an insulation resistance detection circuit 49 circuit for diagnosing insulation resistance deterioration in the detector is provided, and the flow rate measurement circuit ( SW the excitation circuit 45) and the insulation resistance diagnostic circuit 49.
・ It is configured to switch by a relay. That is,
When measuring insulation resistance, the connection with the excitation circuit 45 shown in FIG. 3 is cut off by a relay (relay control signal 47), and the coil in the detector and the insulation resistance measurement circuit 49 are connected by a relay (relay control signal 47). To do.

When the DC voltage shown in FIG. 4 is Vchk, the detection resistance is Rdet, the insulation resistance is Rz, and the voltage between the detection resistances is Vdet, the insulation resistance Rz is given by the following equation.

[0028]     Rz = {(Vchk / Vdet) -1} × Rdet (2)

An insulation resistance detection circuit 49 for measuring the insulation resistance of the coil resistance is shown in FIG. As shown in FIG. 5, the A / D converter 4 is provided in the insulation resistance detection circuit 49.
9a and the buffer / amplifier 49b are connected in series, and the buffer / amplifier 49b is connected to the detection resistor 49c and the relay or analog switch 49d. One end of the detection resistor 49c has a coil (excitation coil) 50 in the detector.
It is connected to the coil insulation resistance 52 connected to. Then, a voltage is applied between the exciting coil and the ground electrode, and the insulation resistance is measured by the flowing current. In this example, direct current is used, but alternating current can be used.

[0030]

In the electromagnetic flowmeter in which the exciting circuit and the earth electrode are insulated, a voltage is applied between the exciting coil and the earth electrode, and the insulation resistance between the exciting coil and the earth electrode is measured from the current flowing therethrough. It becomes possible to detect the insulation deterioration of the coil portion, and it is possible to detect whether the flow rate measurement is normally performed. In this case, the excitation method is limited, but there is an advantage that online monitoring is possible.

Even if the exciting circuit and the earth electrode are insulated by connecting the exciting circuit and the insulation resistance measuring circuit in parallel to the exciting coil and switching them by SW of a relay or the like, the exciting circuit and the earth electrode are insulated. Even if not, it is possible to measure the insulation deterioration of the coil portion, and it is possible to detect whether the flow rate measurement is normally performed. In this case, although the offline monitoring is performed, there is an advantage that the measurement can be performed without depending on the excitation circuit method.

[Brief description of drawings]

FIG. 1 is a circuit block diagram in which the present invention is applied to a two-wire electromagnetic flow meter.

FIG. 2 is a circuit block diagram in which the present invention is applied to a 4-wire electromagnetic flow meter.

FIG. 3 is a circuit block diagram of an excitation circuit used in FIGS. 1 and 2.

FIG. 4 is a circuit block diagram showing an excitation circuit and an insulation resistance detection circuit connected in parallel, and switching means for switching the excitation circuit and the insulation resistance detection circuit.

FIG. 5 is a circuit block diagram showing details of the insulation resistance detection circuit in FIG.

[Explanation of symbols]

45 Excitation circuit 47 Relay control signal 49 Insulation resistance detection circuit 50 coil in the detector 52 Coil insulation resistance

Claims (4)

[Claims] 1. An electric current is supplied from an exciting circuit to an exciting coil in a detector, a magnetic field is generated in the detector, and a voltage proportional to a flow velocity of a conductive fluid to be measured is applied to an electrode in the detector. An electromagnetic flowmeter for detecting a flow rate by detecting with an electromagnetic flowmeter, comprising: a circuit for measuring an insulation resistance between the exciting coil and an earth electrode. 2. The exciting circuit and the earth electrode are insulated from each other, and a voltage is applied between the exciting coil and the earth electrode, so that the current flowing between the exciting coil and the earth electrode is The electromagnetic flowmeter according to claim 1, further comprising a circuit for measuring an insulation resistance between an exciting coil and the ground electrode. 3. An insulation resistance detecting circuit for diagnosing insulation resistance deterioration, and a switching means for switching between the flow rate measuring circuit and the insulation resistance detecting circuit, separately from the flow rate measuring circuit for measuring the flow rate. The electromagnetic flowmeter according to claim 1, wherein: 4. The insulation resistance detection circuit measures insulation resistance between the exciting coil and the ground electrode, which is electrically insulated from the flow rate measurement circuit by the switching means. Item 3. The electromagnetic flowmeter according to Item 3.