JPH09210745A - Capacitive electromagnetic flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To judge whether or not an environment condition in relation to a measurement fluid is normal by providing a switching means (switch) or the like that switches a guard electrode between an operational amplifier and a frequency generation circuit. SOLUTION: When a common terminal 42c of a switch 42 is connected to a switching terminal 42a, a signal processing circuit 44 calculates a flow rate signal by utilizing output signals of operational amplifiers 40, 41 and outputs the signal from an output terminal 45. When an environment condition of a measurement fluid is detected, the common terminal 42c is connected to a switching terminal 42b. In this condition, a frequency signal Vo is applied to guard electrodes 39a, 39b from a frequency generation circuit 43. The amplifier 40 receives the signal Vo via the measurement fluid and a detection electrode 36 and outputs it to one of the input terminals of the processing circuit 44 from the output terminal. On the other hand, the amplifier 41 receives it without passing through the measurement fluid and outputs it to the other input terminal of the processing circuit 44. In the processing circuit 44, a characteristic curve corresponding to the environment condition of the measurement fluid can be obtained from output signals Vf of the amplifiers 40, 41.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitive electromagnetic flowmeter that converts a flow rate of a measurement fluid into an electric signal and outputs a flow rate signal corresponding to the flow rate through an electrostatic capacitance, and particularly relates to the measurement fluid. The present invention relates to a capacity type electromagnetic flow meter improved so that it can be discriminated whether or not the environmental conditions to be met are normal.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an outline of the configuration of a conventional capacitive electromagnetic flowmeter. This type of configuration is Japanese Patent Application No. 5-8
No. 6061 (Japanese Patent Laid-Open No. 6-300596) "Title of Invention: Capacitive Electromagnetic Flowmeter", the main points of which are described below.

Reference numeral 10 denotes an exciting circuit, which supplies an exciting current _If to the exciting coils 11A and 11B with a predetermined waveform and frequency and outputs a timing signal T ₁ required for signal processing to the converter 12.

The exciting coils 11A and 11B are excited by the exciting current I _f.
A magnetic field B having a waveform and frequency corresponding to is applied to the measurement fluid Q. The detection electrodes 13A and 13B are insulated from the measurement fluid Q and fixed to the insulating conduit 14. These detection electrodes 13A and 13B are the preamplifier 1 of the conversion unit 12.
The input terminals of 5A and 15B are connected via terminals T _A and T _B.

The electric signals appearing at the output terminals of the preamplifiers 15A and 15B are subjected to a differential operation by the differential amplifier 16 and output to the signal processing circuit 17. The signal processing circuit 17 executes signal processing using the timing signal T ₁ and outputs it to the output end 18 of the conversion unit 12 as a flow rate signal.

In such a structure, when the measuring fluid Q flows into the conduit 14, the measuring fluid Q enters inside the conduit 14.
The electromotive force corresponding to the flow rate is generated. This electromotive force is output to the input ends of the preamplifiers 15A and 15B via the capacitances C _A and C _B (values of several tens of pF) formed between the measurement fluid Q and the detection electrodes 13A and 13B. Has been done.

Since the input side of the preamplifiers 15A and 15B has a high impedance, the preamplifiers 15A and 15B convert this into a low impedance and output it to the differential amplifier 16, where common mode noise and the like are removed. And outputs it to the signal processing circuit 17. The signal processing circuit 17 calculates a flow rate signal by a predetermined flow rate calculation program and outputs it to the output end 18.

In such a capacitance type electromagnetic flow meter, in order to detect that the measuring fluid Q in the conduit 14 is emptied without contacting the measuring fluid Q, for example, the actual opening 57 It is conceivable to apply a capacitance detection type detection means as disclosed in Japanese Patent No. 63223.

Hereinafter, the main points of this point will be described with reference to FIGS. 6 and 7. FIG. 6 is a sectional view of the detector. FIG. 7 is a circuit diagram showing a configuration of a converter connected to the detector shown in FIG.

In FIG. 6, the conduit 20 is a conductive conduit 2
An insulative lining 22 is formed on the inner peripheral surface of No. 1 by lining. Detection electrodes 23a and 23b for detecting a flow rate signal are fixed to the wall of the pipe 20 so as to be in contact with the measurement fluid 24 while being insulated from the conduit 21. Then, although not shown, the measurement fluid 2 is supplied from the outside of the conduit 20.
A magnetic field is applied to 4.

Further, these detection electrodes 23a, 23b
Separately from the above, electrodes 26a and 26b, to which the lead wires 25a and 25b are connected, respectively, are provided so as to be insulated from the lining 22 through a hole 27 provided above the conduit 21.

A capacitance C _Q is formed between the detection electrodes 23a and 23b through the measuring fluid 24, and lead wires 25a and 2 connected to the detection electrodes 23a and 23b are connected.
A secondary winding of the transformer T and a resistor 28 having a resistance value R are connected in series between 5b as shown in FIG.

An AC power supply 29 is connected to the primary winding of the transformer T, and the detection electrode 26a, the measuring fluid 24, and the detection electrode 26 are connected from the AC power supply 29 through the secondary winding.
b, an alternating current is passed through the resistor 28 to generate a voltage e _R across the resistor 28.

A base and an emitter of a transistor 30 are connected to both ends of the resistor 28, and a diode 31 for protecting the transistor 30 is connected in parallel.

Further, a coil 32a of the relay 32 and a DC power supply 33 are connected in series between the collector and the emitter of the transistor 30, and the relay 32b of the relay 32 is connected.
A capacitor 34 for stabilizing the operation of the contact 32b is connected in parallel with the coil 32a.

In this case, the resistance value R, the voltage of the AC power supply 29, and the frequency thereof are selected so that e _R > V _be when the inside of the pipe 20 is filled with the measurement fluid 24. deep. However, V _be is the base of the transistor 30 /
It is the forward voltage between the emitters.

In the above structure, the measurement fluid 24
When is full of water, the condition of e _R > V _be is satisfied.
The transistor 30 is turned on, current flows through the coil 32a, the b contact 32b is opened, and no alarm is given to the outside.

However, since the capacitance C _Q between the detection electrodes 23a and 23b becomes small when the water is not full,
Since e _R <V _be , the transistor 30 is cut off, the relay 32 is deenergized, and the b contact 32b is closed, whereby the alarm device operates.

[0019]

However, an electromagnetic flowmeter which detects whether the measured fluid is full or not by simply using the change due to the magnitude of the capacitance as described above is used when the conductivity of the measured fluid is large. At any rate, when the conductivity is extremely small, for example, 0.01 μS / cm, the change is small between full water and non-full water, and it is difficult to detect effectively.

Furthermore, when measuring the flow rate of a measuring fluid having a low conductivity, the conductivity is often at the lower limit of measurement, so that the environment of whether the conductivity of the measuring fluid is within the measuring range or not. It is also necessary to make a distinction.

[0021]

In order to solve the above-mentioned problems, the present invention mainly comprises a conduit made of an insulating material for flowing a measurement fluid and a magnetic field applied to the measurement fluid. Exciting means, a pair of detection electrodes for detecting the signal voltage generated in the previous measurement fluid through the capacitance formed by the previous conduit, and a gap between these detection electrodes in the circumferential direction. And a pair of guard electrodes divided and arranged to hold the above, a pair of amplifying means for controlling the potentials of the preceding guard electrode and the preceding detection electrode to be the same, and a frequency generating means for generating a predetermined frequency signal. And a switching means for switching the previous guard electrode between the previous amplification means and the previous frequency generation means, and the previous amplification obtained in a state where the previous frequency signal is applied to the previous guard electrode by this switching means. Difference in frequency characteristics of output of means From those which is adapted to detect the environmental conditions associated with the previous measurement fluid.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention. The conduit 35 is made of an insulating material, and the outer wall of the conduit 35 has the detection electrode 3 with respect to the center of the conduit 35.
6 and 37 face each other and are fixed in an arc shape.

Furthermore, the guard electrodes 38a, 38b and the guard electrodes 39a, 39b are arranged in a divided manner with a gap therebetween in the direction in which they are circumferentially separated from the detection electrodes 36, 37.

The non-inverting input terminal (+) of the operational amplifier 40 is connected to the detection electrode 36, and the inverting input terminal (-) thereof is connected to the output terminal and to the guard electrodes 38a and 38b.

The non-inverting input terminal (+) of the operational amplifier 41 is connected to the detection electrode 37, and the inverting input terminal (-) of the operational amplifier 41 is connected to the output terminal, and is connected to the guard electrodes 39a and 39b via the switch 42. It is connected.

The common end 42c of the switch 42 is connected to the guard electrodes 39a and 39b, one switching end 42a of which is connected to the inverting input end (-) of the operational amplifier 41 and the other switching end 42b. Are connected to the frequency generation circuit 43.

The frequency generating circuit 43 is for generating a frequency signal V _O having a constant amplitude and having a SIN-like waveform whose frequency f can be varied as required.

The common end 42c of the switch 42 is the switching end 42.
When connected to a, the signal processing circuit 44 incorporating a microcomputer calculates a flow rate signal using the signal V _Q output from the operational amplifiers 40 and 41 and outputs it to the output end 45 thereof.

When the common end 42c of the switch 42 is connected to the switching end 42b, the signal processing circuit 44 calculates the frequency characteristic by using the signal V _f output from the operational amplifiers 40 and 41, and outputs the frequency characteristic. Output to the output terminal 45.

Next, the operation of the embodiment thus configured will be described with reference to the characteristic diagrams shown in FIGS. 2, 3 and 4. First, the operation in the normal flow rate measurement state will be described. At this time, the common end 42c of the switch 42 is connected to the switching end 42a.

In this state, both the operational amplifiers 40 and 41 operate so that the inverting input terminal (-) and the non-inverting input terminal (+) have the same potential.
1 can detect the signal voltage generated in the measurement fluid without being affected by the stray capacitance existing in the vicinity of the detection electrodes 36 and 37. The signal processing circuit 44 executes the flow rate calculation using the detection results detected by the operational amplifiers 40 and 41, and outputs it to the output end 45.

Next, the case of detecting the environmental conditions of the measurement fluid will be described. In this case, the common end 42c of the switch 42 is connected to the switching end 42b. In this state, the frequency generating circuit 43 applies a frequency signal V _O having a constant amplitude which changes in a SIN manner to the guard electrodes 39a and 39b.

Then, the operational amplifier 40 receives this frequency signal V _O via the measurement fluid and the detection electrode 36, and outputs it from the output end thereof to one end of the input of the signal processing circuit 44.
On the other hand, the operational amplifier 41 receives without passing through the measurement fluid and outputs it to the other end of the input of the signal processing circuit 44.

In this way, the signal processing circuit 44 receives the signal V obtained at the output terminals of these operational amplifiers 40 and 41.
_f is divided by the frequency signal V _O (V _f / V _O ) and its amplitude G
The change between A and the phase PH is calculated and stored in a built-in memory or the like.

This calculation is executed for each frequency f by changing the frequency f of the frequency signal V _O in the range of 10 Hz to 40 MHz, for example. As a result, characteristic curves as shown in FIGS. 2 to 4 are obtained corresponding to the environmental conditions of the measured fluid.

The characteristic curve shown in FIG.
3 is not filled with water, the characteristic curve shown in FIG. 3 shows that the measured fluid is in the normal state of the conduit 35 (conductivity is 0.2 μS / c).
m), the characteristic curve shown in FIG. 4 shows the respective characteristic curves when the range of the conductivity of the measured fluid is 0.01 μS / cm, which is the lower limit of measurement.

In the unfilled state shown in FIG. 2, the amplitude GA has a substantially flat characteristic up to 10 KHz, and in the filled state shown in FIG. 3, the amplitude GA shows a characteristic that the amplitude GA increases linearly up to 1 KHz. From this difference, it is possible to distinguish between full water and non-full water. Further, when the conductivity is at the lower limit of the measurable range, as shown in FIG. 4, the attenuation of the amplitude GA in a state where the frequency f is low is not so large as when the water is full.

As described above, since there are large differences in the frequency characteristics depending on the environmental conditions of the fluid to be measured, it is possible to judge from this frequency characteristic whether the water is full, non-full, or out of the lower limit of the conductivity.

However, even if the frequency is not changed in this way, when the frequency characteristic of the fluid to be measured is known in advance, the environmental condition can be determined only by detecting the attenuation of the amplitude GA with respect to the specific frequency. .

For example, this is set to 20 as a fixed frequency f.
Focusing on the point M of each characteristic diagram, which is the point of Hz, the amplitude GA is approximately 0.9 from FIG. 2, the amplitude GA is approximately 0.03 from FIG. 3, and the amplitude GA is approximately 0.4 from FIG. Can be asked.

Therefore, when the amplitude GA is in the range of 0.4 to 0.9, it indicates that the water is not full or the lower limit of the conductivity is exceeded, and it can be judged that the measurement is impossible.
When the amplitude GA has a value smaller than 1 by about two digits, it can be determined that the measurement state is normal.

Whether or not the measurement state is normal is determined by the signal processing circuit 4 even when the flow rate is being measured normally.
The common end 42c of the switch 42 by the switching signal from
Can be automatically executed at any time by switching from the switching end 42a to the switching end 42b at a constant time interval.

[0043]

As described above in detail with reference to the embodiments of the present invention, according to the present invention, in the capacitive electromagnetic flowmeter, the frequency signal is applied to the guard electrode by the switching means and is obtained at the detection electrode. From the difference in the frequency characteristics of the generated signals, it is possible to detect the environmental condition related to the measurement fluid as needed without contacting the measurement fluid.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a characteristic diagram showing characteristics when the embodiment shown in FIG. 1 is not full of water.

FIG. 3 is a characteristic diagram showing characteristics when the embodiment shown in FIG. 1 is full of water.

FIG. 4 is a characteristic diagram showing characteristics at the lower limit conductivity in the embodiment shown in FIG.

FIG. 5 is a configuration diagram showing a configuration of a conventional capacitive electromagnetic flow meter.

FIG. 6 is a configuration diagram showing a configuration of a detector of a conventional electromagnetic flow meter that detects non-full water.

7 is a configuration diagram showing a configuration of a converter coupled with the electromagnetic flowmeter shown in FIG.

[Explanation of symbols]

10 Excitation Circuit 11A, 11B Excitation Coil 12 Converter 13A, 13B, 23a, 23b, 36, 37 Detection Electrode 14, 21, 35 Conduit 15A, 15B Preamplifier 16 Differential Amplifier 17 Signal Processing Circuit 20 Pipeline 22 Lining 26a , 26b electrode 30 transistor 38a, 38b, 39a, 39b guard electrode 40, 41 operational amplifier 42 switch 43 frequency generation circuit 44 signal processing circuit

Claims (3)

[Claims] 1. A conduit made of an insulating material for flowing a measurement fluid, and an excitation means for applying a magnetic field to the measurement fluid,
A pair of detection electrodes for detecting the signal voltage generated in the measurement fluid via the electrostatic capacitance formed by the conduit, and a plurality of detection electrodes which are spaced apart from each other and are arranged in a circumferential direction with a gap maintained therebetween. A pair of guard electrodes, a pair of amplification means for controlling the potentials of the guard electrode and the detection electrode to be the same, a frequency generation means for generating a predetermined frequency signal, and the guard electrode for the amplification means. And a switching means for switching between the frequency generating means and the frequency generating means, which is related to the measurement fluid from the difference in frequency characteristic of the output of the amplifying means obtained by applying the frequency signal to the guard electrode by the switching means. Capacitive electromagnetic flowmeter characterized by detecting environmental conditions. 2. The capacity type electromagnetic flowmeter according to claim 1, wherein whether or not the inside of the conduit is filled with a measurement fluid is detected as the environmental condition. 3. The capacitive electromagnetic flowmeter according to claim 1, wherein whether or not the environmental condition is a conductivity within a measurable range of the measurement fluid is detected.