JPH11118549A - Electromagnetic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a more stabilized measured flow rate. SOLUTION: Capacitors 21A, 21B are interposed between electrodes 12A, 12B and buffers 22A, 22B and connected in parallel with switches 24A, 24B. A flow rate monitoring section 7 monitors flow rate of fluid in a pipe 11 and the switches 24A, 24B are turned on only when the flow rate drops down to a specified threshold value thus detecting the state where the pipe 11 is not filled with water. Alternatively, zero flow rate is set as the threshold value and the state where the pipe 11 is not filled with water is detected only when the flow rate is zero.

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, and more particularly to an electromagnetic flow meter having a non-full level detection function for determining whether a fluid to be measured in a pipe is full.

[0002]

2. Description of the Related Art Generally, in this type of electromagnetic flowmeter, a magnetic field is applied to a pipe fluid, and a signal electromotive force having an amplitude corresponding to the fluid flow velocity is detected by an electrode arranged on the inner wall of the pipe. Then, the fluid flow rate is calculated. Therefore, when measuring the flow rate, it is assumed that the electrode is always in a state of being in contact with the fluid, that is, in a full state.

FIG. 5 is an explanatory diagram showing a full / non-full state. In FIG. 5A, since the fluid is in contact with both of the electrodes 12A and 12B opposed to the inner wall of the tube 11, the signal electromotive force generated in the fluid can be detected by the electrodes 12A and 12B. That is, it is full. On the other hand, FIG.
In (b), since the fluid is not in contact with both the electrodes 12A and 12B, the signal electromotive force generated in the fluid is applied to the electrodes 1A and 12B.
It is in a state that cannot be detected by 2A and 12B, that is, in a non-full state (empty state).

Here, when the flow of the fluid is stopped in a full state, no signal electromotive force is generated and the flow rate becomes zero. However, even in a non-full state, the electrodes 12A and 12B are not in contact with the liquid. , No signal electromotive force is detected and the flow rate becomes zero. However, depending on the process, it may be necessary to determine the validity / invalidity of the flow rate value detected immediately before the non-full level, or may require a predetermined control according to the non-full level. Therefore, a function for distinguishing and detecting these different states is required.

Conventionally, to meet such demands, there has been proposed an electromagnetic flow meter which applies a slight DC current to the electrodes 12A and 12B and detects a non-full state by a change in potential of the electrodes 12A and 12B (see, for example, Japanese Patent Application Laid-Open No. H11-157556). For example, JP-A-8-2
No. 1756). FIG. 6 is a block diagram showing a conventional electromagnetic flow meter. In a detector 10, a magnetic field is applied to a fluid in a tube 11 by a coil 13 based on an AC exciting current of a predetermined rectangular wave, and a signal generated in the fluid is generated. Power to electrode 1
Detected by 2A and 12B and output as detection signals 1A and 1B.

The converter 1 outputs an AC exciting current from the exciting unit 8 to the detector 10, and outputs the detection signals 1 A and 1 B from the detector 10 to the operational amplifier 2 of the AC amplifying unit 2.
3, the signal is amplified by the signal processing unit 3, and A
-D conversion processing is performed, and the arithmetic processing unit 4 calculates and outputs the fluid flow rate in the pipe 11. In particular, the transducer 1 has electrodes 12A,
A current controller 5 for applying a slight current to the electrode 12B,
An empty detector for detecting a non-full level according to the potentials of 2A and 12B is provided.

At the time of non-full detection, the power supply potential + V, via the resistors 51A, 51B and the switches 52A, 52B.
−V is applied to the electrodes 12A and 12B, and a very small detection current flows to the ground electrode (earth ring) 12C via the fluid in the tube 11. Here, in the non-full state, the detection current does not flow because one or both of the electrodes 12A and 12B are not in contact with the fluid, and the
The potentials of A and 12B are substantially equal to the power supply potentials + V and -V.

The potentials of the electrodes 12A and 12B are supplied to the comparators 61A and 61A of the empty detector 6 via buffers 22A and 22B.
61B. Here, a predetermined threshold voltage V
a, Vb to determine whether or not the potential indicates a non-full level, and the arithmetic processing unit 4 notifies the higher-level process control device according to the determination results 62A, 62B.

The switches 52A, 5A of the current control unit 5
2B is based on a detection instruction signal 41 from the arithmetic processing unit 4.
On / off control is performed intermittently at a predetermined cycle. Thereby, compared with the case where a current is always applied to the electrodes 12A and 12B, the electrodes 12A and 12B are caused by the application of the current.
The generation rate of the insulator generated on the surface of 12B decreases,
The flow measurement with little error has been realized for a long time.

[0010]

However, in such a conventional electromagnetic flow meter, the electrodes 12A, 12A of the tube 11 are not provided.
B is directly connected to the inputs of the buffers 22A and 22B, so that the electrodes 12A and 12B
There is a problem that the measured flow rate is not stable due to leakage current to the electrodes 12A and 12B and the buffer 2
In the case where a capacitor is provided between 2A and 22B, there is a problem that the DC potential of the electrodes 12A and 12B is not supplied to the empty detector 5 and non-full level detection cannot be performed.

The switches 52A, 52 of the current control unit 5
2B, the current is intermittently applied to the electrodes 12A and 12B of the tube 11, so that the detection signal 1 having an amplitude corresponding to the flow velocity due to the application of the current.
A and 1B also changed, and there was a problem that the measured flow rate was unstable, albeit slightly. The present invention has been made to solve such a problem, and has as its object to provide an electromagnetic flowmeter capable of obtaining a more stable measurement flow rate.

[0012]

In order to achieve the above object, an electromagnetic flowmeter according to the present invention comprises a pair of capacitors respectively connected in series between a corresponding electrode and an operational amplifier, and a pair of capacitors. A pair of switches for inputting the DC potential of the corresponding operational amplifier to a corresponding operational amplifier, a current controller for applying a predetermined DC current for non-full level detection to each electrode, and a DC applied to the electrodes from the current controller. The output of each operational amplifier that changes according to the current is compared with a reference potential, and based on the comparison result, an empty detection unit that detects a non-full state of the fluid to be measured and a flow rate of the fluid to be measured are monitored. In some cases, the switch is turned off and the stop of the DC current from the current control unit is instructed. When the flow rate of the fluid to be measured falls below a predetermined threshold, the switch is turned on and the DC current from the current control unit is Application of Those comprising an instruction to the flow rate monitoring unit.

A pair of capacitors respectively connected in series between the corresponding electrode and the operational amplifier; a current control unit for applying a predetermined direct current for detecting non-full level to each electrode; An empty detector that compares the potential of the electrode, which changes according to the DC current applied to the electrode from the unit, with a reference potential, and detects a non-full state of the fluid to be measured according to the comparison result; A pair of switches connected in series between the detection unit and the flow rate of the fluid to be measured are monitored, and in normal times, the switch is turned off and an instruction to stop DC current from the current control unit is issued. And a flow monitoring unit for turning on the switch and instructing the application of a direct current from the current control unit when the pressure falls below a predetermined threshold value.

The flow rate monitoring unit monitors the flow rate of the fluid to be measured, and normally turns off the switch and instructs to stop the DC current from the current control unit, so that the flow rate of the fluid to be measured becomes zero. In such a case, the switch is turned on and the application of the direct current from the current control unit is instructed. Therefore, only when the flow rate becomes equal to or less than the predetermined threshold value or when the flow rate becomes zero, a slight DC current is applied to the electrode to detect non-full level, and normal flow rate measurement is performed. Sometimes, no DC current is applied to the electrodes, and leakage current from the operational amplifier to the electrodes is cut off.

[0015]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an electromagnetic flow meter according to an embodiment of the present invention, in which the same or equivalent parts as those described above (FIG. 6) are denoted by the same reference numerals. In the present invention, immediately before the non-full state, the flow rate of the fluid to be measured in the pipe always drops to near zero, and the flow rate drops to a predetermined threshold value, focusing on the fact that the flow rate becomes zero in the non-full state. In this case, the non-full level is detected only when the flow rate becomes zero.

In the example shown in FIG. 1, the capacitors 21A and 21B are different from the conventional configuration (see FIG.
A and 22B are arranged before. The switches 24A, 2B are connected in parallel with the capacitors 21A, 21B, respectively.
4B is provided, and in the case of non-full level detection, the current control unit 5 is controlled to turn on in synchronization with the switches 52A and 52B. Thus, at the time of non-full detection, the potentials of the detection signals 1A and 1B are input to the empty detection unit 6 via the switches 24A and 24B and the buffers 22A and 22B.

The flow rate monitoring section 7 calculates a flow rate (or flow rate) calculated by the arithmetic processing section 4 based on a flow rate signal 42.
The flow rate of the fluid flowing through the pipe 11 is monitored. FIG. 2 is a timing chart showing the operation of the flow monitoring unit, and FIG. 3 is a flowchart showing the operation of the flow monitoring unit. The flow rate monitor 7 constantly compares the flow rate W of the fluid flowing in the pipe 11 with a predetermined threshold value W0 (step S1).

At time T1, the flow rate W becomes equal to the threshold value W0.
If it has dropped below (step S1: YES),
The switches 52A and 52B and the switches 24A and 24B are turned on by the detection instruction signal 71 (step S2). This causes a slight DC current to flow through the switch 5
2A and 52B, the DC potential of the electrodes 12A and 12B is applied to the switches 1A and 12B.
The data is input to the buffers 22A and 22B via the 2A and 12B, and the empty detector 5 detects non-full level.

On the other hand, if the flow rate W exceeds the threshold value W0 at time T2 (step S1: NO), the switch 5
2A, 52B and switches 12A, 12B are turned off (O
FF) (step S3). This stops the current application from the switches 52A and 52B,
Buffers 22A, 22 are provided by capacitors 21A, 21B.
The leakage current from B to the electrodes 24A and 24B is cut off, and the non-full level detection ends.

As described above, the capacitors 21A and 21B for removing low frequency components from the detection signals 1A and 1B are connected to the electrodes 1A and 1B.
2A, 12B and buffers 22A, 22B, and switches 24A, 24B in parallel with the capacitors 21A, 21B.
The fluid flow rate in the pipe 11 is constantly monitored, and only when the flow rate falls to a predetermined threshold value, the switches 24A and 24B are closed to detect non-full water.

Therefore, the non-full level detection is performed only when the flow rate measurement is not so required, so that there is no influence on the flow rate measurement. When measuring the flow rate, the electrode 12
Leakage current from the buffers 22A and 22B to A and 12B is cut off, and more stable flow measurement can be realized.
Further, power consumption for non-full level detection can be reduced, and even with a configuration that operates with a small amount of power supply, which is unique to this type of field device, a non-full level state can be reliably detected.

After the zero flow rate is detected by the flow rate monitoring unit 7, it is determined by the non-full level detection whether the zero flow rate is due to the stoppage of the flow in the full state or the measurement failure in the non-full state. You may make it. In this case, zero is set as the threshold value W0. Thereby, during the flow rate measurement, the electrodes 12A,
Unnecessary current application to 12B is suppressed, and stable flow measurement can be always realized.

In FIG. 1, since the influence on the measured flow rate by the comparators 61A and 61B is slight, the buffer 2
The comparators 61A and 61 of the empty detector 6 are connected to the outputs of 2A and 22B.
B is always connected. However, the comparators 61A and 61A
A switch that operates in synchronization with the switches 52A and 52B is provided at the input of B, and the buffer 22 is provided only when non-full water is detected.
The outputs of A and 22B may be input to the comparators 61A and 61B.

In FIG. 1, the electrodes 12A, 12B are output from the buffers 22A, 22B of the AC amplifier 2.
Has been described by way of example, where the potentials are compared by the sky detection unit 6, but the present invention is not limited to this. FIG. 4 is a block diagram showing an electromagnetic flow meter according to another embodiment of the present invention. In this case, a detection instruction signal 7 from a flow monitor 7 is provided.
Switch 63 that is turned on only when non-full water is detected according to 1.
The potentials of the electrodes 12A and 12B are supplied to the empty detector 6 via A and 63B.

Therefore, the current control unit 5 and the empty detection unit 6 can be completely separated from the flow rate measuring system by the switches 52A and 52B except when the non-full state is detected. Compatible with non-full water detection. It should be noted that the resistors 51A and 51B of the current control unit 5 and the switches 52A and 5A are connected as shown by broken lines in FIG.
The potentials of the electrodes 12A and 12B may be compared by the empty detection unit 6 based on the potential at the connection point with 2B, and the switches 63A and 63B become unnecessary.

In the above description, the flow rate monitor 7
Although the description has been given of the case where the fluid flow rate in the pipe 11 is monitored, the fluid flow rate may be monitored, and the non-full level detection may be performed when the flow rate becomes equal to or less than a predetermined threshold value.

[0027]

As described above, according to the present invention, a capacitor is provided between an operational amplifier for amplifying a signal electromotive force from each electrode and an electrode so that the flow rate of the fluid to be measured is equal to or less than a predetermined threshold value. Only when the voltage drops to zero, a switch provided in parallel with the capacitor is turned on, the DC potential of the electrode is input to the operational amplifier, and empty detection is performed based on the output. Also, only when the flow rate of the fluid to be measured falls below a predetermined threshold value or drops to zero,
A switch connected in series between the electrode and the empty detector is turned on to perform empty detection based on the DC potential of the electrode.

Therefore, the leakage current applied to the electrodes from the operational amplifier is suppressed, and more stable flow rate measurement can be realized, as compared with the conventional case where non-full water is intermittently detected. Further, power consumption for non-full level detection can be reduced, and even with a configuration that operates with a small amount of power supply, which is unique to this type of field device, a non-full level state can be reliably detected. In addition, only when the flow rate becomes zero, the detection current is applied to the electrode to perform the non-full level detection, so that during the flow rate measurement, unnecessary current application to the electrode is suppressed. Stable flow measurement can be realized.

[Brief description of the drawings]

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

FIG. 2 is a timing chart showing an operation of a flow monitoring unit.

FIG. 3 is a flowchart illustrating an operation of a flow monitoring unit.

FIG. 4 is a block diagram showing an electromagnetic flow meter according to another embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a full / non-full state.

FIG. 6 is a block diagram showing a conventional electromagnetic flow meter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Converter, 1A, 1B ... Detection signal, 2 ... AC amplifier,
21A, 21B: capacitor, 22A, 22B: buffer, 23: operational amplifier, 24A, 24B: switch, 3
... Signal processing unit, 4 ... Operation processing unit, 42 ... Flow rate signal, 5 ...
Current control unit, 51A, 51B ... resistance, 52A, 52B ...
Switch, 6: Empty detector, 61A, 61B: Comparator, 6
2A, 62B ... judgment result, 63A, 63B ... switch,
7: flow rate monitoring unit, 71: detection instruction signal, 8: excitation unit, 1
0: detector, 11: tube, 12A, 12B: electrode, 12C
... ground electrode, 13 ... coil.

Claims (3)

[Claims] An operational amplifier for detecting a signal electromotive force corresponding to a flow rate of a fluid to be measured by a pair of electrodes disposed opposite to each other in a pipe through which a fluid to be measured flows, and for corresponding a signal electromotive force from each electrode. And a pair of capacitors respectively connected in series between the corresponding electrode and the operational amplifier in an electromagnetic flowmeter for measuring the flow rate of the fluid to be measured based on signals obtained from the operational amplifiers. A pair of switches for inputting the DC potential of the electrode to a corresponding operational amplifier; a current control unit for applying a predetermined DC current for non-full detection to each electrode; and a current control unit applied to the electrodes from the current control unit. The output of each operational amplifier that changes according to the DC current is compared with a reference potential, and based on the comparison result, an empty detection unit that detects a non-full state of the fluid to be measured, and monitors the flow rate of the fluid to be measured, Through In some cases, the switch is turned off and the stop of the DC current from the current control unit is instructed. When the flow rate of the fluid to be measured falls below a predetermined threshold, the switch is turned on and the DC current from the current control unit is turned off. And a flow rate monitoring unit for instructing application of pressure. 2. An operational amplifier for detecting a signal electromotive force corresponding to a flow rate of a fluid to be measured by a pair of electrodes disposed opposite to each other in a pipe through which a fluid to be measured flows, and for corresponding a signal electromotive force from each electrode. And a pair of capacitors respectively connected in series between the corresponding electrode and the operational amplifier in an electromagnetic flowmeter for measuring the flow rate of the fluid to be measured based on signals obtained from the operational amplifiers. A current control unit that applies a predetermined DC current for non-full level detection to the electrode, and a potential of the electrode that changes according to the DC current applied from the current control unit to the electrode is compared with a reference potential, and the comparison is performed. An empty detection unit that detects the non-full state of the fluid to be measured according to the result, a pair of switches connected in series between each electrode and the empty detection unit, and monitors the flow rate of the fluid to be measured. Switch When the flow rate of the fluid to be measured drops below a predetermined threshold value, the switch is turned on and the application of the DC current from the current control unit is instructed. An electromagnetic flowmeter, comprising: 3. The electromagnetic flowmeter according to claim 1, wherein the flow rate monitoring unit monitors the flow rate of the fluid to be measured, and in a normal state, turns off the switch and instructs to stop the DC current from the current control unit. When the flow rate of the fluid to be measured becomes zero, the switch is turned on and the application of a direct current from the current control unit is instructed.