JPH06341875A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To measure an insulation impedance even when a pipe to be measured is filled with water. CONSTITUTION:A switch 20 is provided between a fluid potential detection means 6 and a flowmeter common line 14. By opening the switch 20, insulation impedances 19 (Zi) between both of signal detection electrodes 2, 3 and signal lines and the flowmeter common line 14 can be measured even when a pipe is filled with water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal detection electrode for detecting a signal electromotive force generated in an electromagnetic flowmeter, a signal line connecting the electrode and the converter, and an electrical insulation between a flowmeter common line. The present invention relates to an electromagnetic flow meter capable of measuring (insulation impedance) even when the measuring tube is full of water.

[0002]

2. Description of the Related Art FIG. 2 is a schematic diagram showing a general electromagnetic flowmeter. That is, the electromagnetic flowmeter is roughly divided into a detection unit as a sensor main body and a conversion unit that processes a signal obtained by the detection unit. Here, the detection unit is the signal detection electrodes 2 and 3 attached to the measuring tube 1, the signal lines 4 and 4.
5, a fluid potential detecting means 6 composed of an earth ring or an earth electrode, an exciting coil 7 and the like, and a converting portion is an exciting power source 10, preamplifiers 11 and 12, a differential amplifier 13, A /
The D converter 15 and the processing device (CPU unit) 16 are included. In addition, 8 is earth and 14 is a flow meter common line.

The operation will be described. For the conductive fluid flowing in the measuring tube 1, from the exciting power source 10 to the exciting coil 7
It is well known that when a magnetic field is excited by applying a magnetic field, an electromotive force proportional to the flow velocity is generated in the direction in which the fluid flows and the direction perpendicular to the magnetic field. When this electromotive force is detected by a pair of electrodes 2 and 3 facing each other and is applied to the conversion unit via the signal lines 4 and 5, the applied signal is once received by the preamplifiers 11 and 12 having high input impedance in the conversion unit. After that, the difference is obtained by the differential amplifier 13.

The reference potential required at this time is a detecting means 6 for detecting the fluid potential such as an earth ring or an earth electrode.
Is transmitted to the common line 14 of the flowmeter. At this time, the flow meter common line 14 is often grounded as shown. The signal amplified by the differential amplifier 13 is converted into a digital amount by the A / D converter 15, and CP
It is given to the U unit 16. The CPU unit 16 processes this signal and outputs an output according to the flow rate or the flow velocity.

The insulation impedance of FIG. 2 will be described with reference to FIG. In FIG. 3, reference numeral 17 is a detection unit circuit impedance (Zd) composed of electrode wetted impedance and fluid electric resistance, 18 is a signal electromotive force (Ef) proportional to flow velocity, and 19 is an insulation impedance (Zi). ing. Note that reference numerals 2 to 6, 8, 11, 12
And 14 and the like are the same as those shown in FIG.

In such a circuit, the signal electromotive force Ef generated in proportion to the flow velocity is detected by the signal detection electrodes 2 and 3 and given to the preamplifiers 11 and 12 via the signal lines 4 and 5. Here, compared with the detection circuit impedance Zd, the input impedance of the preamplifier and the electrodes 2, 3
If the insulation impedance Zi between the signal lines 4 and 5 and the flow meter common line 14 is sufficiently large, the input voltage Vi to the preamplifiers 11 and 12 is Vi = Ef (1).

However, when the insulation impedance Zi between the electrodes 2, 3, 5 and 14 becomes small due to flooding, Vi = Zi.Ef / (Zi + Zd) (2) Occurs.
Further, when the value of Zi fluctuates, Vi fluctuates, and abnormal fluctuation appears in the output. As described above, the decrease of the insulation impedance Zi is one of the causes of the output abnormality. Therefore, it is necessary to measure the insulation impedance Zi when such an output abnormality occurs or during maintenance.

[0008]

However, conventionally, when the inside of the measuring tube is full of water, the detection circuit impedance 17 (Zd) is present between the electrodes 2 and 3 and the flow meter common line 14.
Since the structure is short-circuited by the fluid potential detecting means 6, the insulation impedance Zi cannot be measured. Therefore, the inside of the measuring tube is once emptied and Zd is set to a sufficiently large value to eliminate the above-mentioned short-circuit state and measure the insulation impedance Zi.

However, in order to empty the inside of the measuring pipe, it is necessary to stop the flow of the fluid once or, if there is a bypass pipe, allow the fluid to flow there. Further, even after emptying the inside of the measuring pipe, there is a complicated problem that accurate insulation measurement cannot be performed unless the fluid adhering to the pipe wall is completely dried. Therefore, an object of the present invention is to provide an electromagnetic flowmeter capable of measuring the insulation impedance while omitting such troublesomeness and keeping the measuring tube full of water.

[0010]

In order to solve such a problem, according to the present invention, a pair of signal detection for detecting a signal electromotive force generated perpendicularly to an applied magnetic field and a flow of fluid flowing in a measuring tube. An electrode, a fluid potential detecting means connected to the common line of the flow meter to detect the potential of the fluid, and a converter for outputting a signal corresponding to the flow velocity or the flow rate of the fluid based on the signals from the fluid potential detecting means and the signal detecting electrode. In an electromagnetic flowmeter comprising at least, a switch is provided between the fluid potential detecting means and the common line of the flowmeter, and the switch is opened so that the signal detecting electrode and the signal detecting electrode serve as a converter. Provide electrical insulation between the connecting signal line and the flow meter common line,
It is characterized in that measurement is possible even when the measuring tube is full of water.

[0011]

A switch is provided between the flow rate signal detecting means and the flow meter common line 14, and the switch is released to reduce the insulation impedance between the signal detection electrode and the signal line and the flow meter common line 14. Be able to measure even when the measuring tube is full of water.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram of a main part showing an embodiment of the present invention. In order to eliminate the annoyance when measuring Zi as described above,
The present invention is characterized in that a switch 20 is provided between the fluid potential detecting means 6 and the flow meter common line 14 as shown in FIG. When the electromagnetic flow meter is normally used, the switch 20 is turned on so that the fluid potential detecting means 6 is connected to the flow meter common line 14, and when the insulation impedance Zi is measured, the switch 20 is turned off to disconnect the electrical connection. By doing so, the short-circuit state as described above is eliminated, and the insulation impedance Zi can be measured even when the measuring tube is full of water.

However, when the flow meter common line 14 is grounded by the ground 8 as shown in FIG. 2 or 3,
The fluid and the flow meter common line 14 may be short-circuited through this ground. Therefore, it is necessary to disconnect the ground 8 when measuring Zi. FIG. 1 shows the situation. In addition, when 2, 3, 4, 5 and 14 are short-circuited through the electric circuit of the conversion unit, it is necessary to further disconnect the connection between the conversion unit and the detection unit and measure Zi.

By doing so, even if the fluid in the measuring tube is not emptied, between the fluid potential detecting means 6 and the flow meter common line 14, and between the signal electromotive force end (18) and the flow meter common line 14. Therefore, Zi can be measured even when the inside of the measuring tube is full of water.

[0015]

According to the present invention, a switch is provided between the flow signal detecting means and the common line of the flow meter, and the switch is released, whereby the signal detecting electrode and the line between the signal line and the common line of the flow meter are connected. It is possible to measure the insulation impedance even when the measuring tube is full of water.

[Brief description of drawings]

FIG. 1 is a circuit diagram of essential parts showing an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an outline of a general electromagnetic flow meter.

FIG. 3 is a partial circuit diagram for explaining the insulation impedance in FIG.

[Explanation of symbols]

1 ... Measuring tube, 2 ... Signal detecting electrode, 3 ... Signal detecting electrode,
4, 5 ... Signal line, 6 ... Fluid potential detecting means, 7 ... Excitation coil, 8 ... Ground, 10 ... Excitation power supply, 11, 12 ... Preamplifier, 13 ... Differential amplifier, 14 ... Flowmeter common line,
15 ... A / D converter, 16 ... Processing device (CPU unit), 17 ... Detector circuit impedance (Zd), 18
… Signal electromotive force (Ef), 19… Insulation impedance (Z
i), 20 ... switch.

Claims (1)

[Claims] 1. A signal electromotive force generated perpendicularly to an applied magnetic field and a fluid flow in a measuring tube is detected.
A pair of signal detection electrodes, a fluid potential detection means connected to the flow meter common line to detect the potential of the fluid, and a signal corresponding to the flow velocity or flow rate of the fluid based on the signals from the fluid potential detection means and the signal detection electrode. In an electromagnetic flowmeter including at least a converter for outputting, a switch is provided between the fluid potential detecting means and a common line of the flowmeter, and the switch is opened to open the signal detecting electrode and the signal detecting electrode. An electromagnetic flowmeter, which is capable of measuring electrical insulation between a signal line connecting the converter to the converter and a common line of the flowmeter even when the measuring tube is full of water.