JPH11101675A - Flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent grounding via a pipe, by providing isolation transformers between an arithmetic circuit generating a current indicating the flow rate of a fluid based on the transmission/reception signals of a transmitter and a receiver and outputting it to a measuring instrument and the transmitter and the receiver respectively. SOLUTION: A current flows in the secondary coil 11b by the magnetic field change generated on the primary coil 11a of isolation transformers 11A, 11B on the transmission side and reception side, and the coils 11a, 11b are electrically insulated. The isolation transformers 11A, 11B are provided between the oscillating circuit 8 of an arithmetic circuit 6 and a transmitter 3 and between the wave-form shaping circuit of the arithmetic circuit 6 and a receiver 4 respectively. The current from the power supply 22 of a measuring instrument 7 flows in a current detection side line 24, thereby the flow meter does not cause grounding, i.e., a phenomenon that the current from the power supply 22 flows to the ground side via a power feed line 23, the arithmetic circuit 6, the transmitter 3, the receiver 4, and a pipe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter for measuring a flow rate of a fluid.

[0002]

2. Description of the Related Art An example of a conventional flow meter is an ultrasonic vortex flow meter shown in FIG. In FIG. 4, a vortex generating column 2 is provided in a pipe 1 through which a fluid flows, and Karman vortices are generated alternately on both sides. The tube 1 is provided with an ultrasonic sensor 5 including transmitters / receivers 3 and 4 made of piezoelectric ceramics such as PZT for transmitting and receiving ultrasonic waves. The transmitters / receivers 3 and 4 are attached to the wall of the tube 1 so as to face each other with the Karman vortex generation region in the tube 1 interposed therebetween. The tube 1 is made of metal and is grounded. Sending
Each of the receivers 3 and 4 has two electrodes (referred to as first electrodes 3a and 4a and second electrodes 3b and 4b, respectively). First electrode 3 of each of transmitter / receiver 3 and 4
Reference numerals a and 4a are connected to the tube 1 via an insulating member such as a silicon resin (not shown).

An arithmetic circuit 6 is connected to the second electrodes 3b and 4b of the transmitters and receivers 3 and 4, respectively. The arithmetic circuit 6 includes a main arithmetic unit 6a provided on the transmitter / receiver 3 or 4 side.
And a sub-operation unit 6b to which a measuring instrument 7 having a display and a recorder (not shown) is connected, and an oscillating signal A and an ultrasonic reception signal B (which will be described later).
In order to indicate the flow rate of the fluid flowing through the tube 1 based on the transmission / reception signals of the power supply line 4 (for example, in FIG.
A current value flowing through a switching circuit 18, an analog output circuit 17, a current detection side line 24, and a closed circuit line formed by a voltage conversion resistor 25 whose one end is grounded, is adjusted. Output.

[0004] The main arithmetic unit 6a is provided with an oscillation signal A having a predetermined frequency.
And an oscillation circuit 8 for inputting the oscillation signal A to the transmitter 3 to transmit ultrasonic waves, an oscillation signal A generated by the oscillation circuit 8 and a signal received by the receiver 4 (ultrasonic reception signal B A) a phase comparison circuit 9 that compares the phase difference of the ultrasonic wave to extract the modulation received from the fluid and outputs it as a fluid change signal H, and a microcomputer that converts the fluid change signal H into a flow signal D indicating the flow rate of the fluid. And a circuit 10.

The microcomputer circuit 10 includes an insulating transformer 11
DC / DC converter 12 (4V / 5V conversion)
An output control circuit 13 to which power is supplied from the secondary circuit 12b is connected, generates a pulse signal E indicating the flow rate of the fluid based on the flow rate signal D, and outputs a photocoupler 40 connected to the output control circuit 13. Is output to the light emitting element 40a.
A filter circuit 1 is provided between the receiver 4 and the phase comparison circuit 9.
4, an amplifier circuit 15, and a waveform shaping circuit 16 are interposed in this order. The filter circuit 14 has a band-pass function, removes noise caused by impact on the transmitter / receiver 3, 4 or the like, and passes the ultrasonic reception signal B containing only fluid information.

The sub-operation unit 6b receives the optical signal corresponding to the pulse signal E output from the light emitting element 40a and receives the signal from the light receiving element 40b to indicate the flow rate of the fluid. An analog output circuit 17 that generates a current (hereinafter, appropriately referred to as a flow current) F, and a primary circuit 12a of the DC / DC converter 12 that supplies power to the analog output circuit 17 are provided.

The primary circuit 1 of the DC / DC converter 12
2a includes a primary coil 11a of the insulating transformer 11 and a switching circuit 18 connected to the primary coil 11a. The secondary circuit 12b of the DC / DC converter 12 includes a secondary coil 11b of the insulating transformer 11,
And a rectifier circuit 19 connected to the secondary coil 11b. Here, the insulation transformer 11 is a primary coil 1
While a current flows through the secondary coil 11b due to the magnetic field change generated by 1a, the primary coil 11a and the secondary coil 11b are electrically insulated. In addition,
The oscillation circuit 8, the phase comparison circuit 9, and the microcomputer circuit 10 are connected to the rectification circuit 19 together with the output control circuit 13, so that power is supplied.

The sub-operation unit 6b has a power supply terminal 20 connected to the switching circuit 18 and a common terminal 21 connected to the analog output circuit 17. Power supply terminal 20
Is connected via a power supply line 23 to a positive pole of a power supply 22 of a predetermined voltage (for example, 24 V) provided in the measuring instrument 7. The negative pole of the power supply 22 is grounded. The common terminal 21 is grounded via a current detection side line 24 and a voltage conversion resistor 25 having a predetermined resistance value (for example, 250Ω) provided in the measuring instrument 7. And the current detection side line 2
4, 4 to 20 mA (for example, 4 mA when the flow rate is 0,
A current (flow current F) of 20 mA flows at the maximum flow rate, and a voltage (flow voltage) having a magnitude corresponding to the flow current F is generated in the voltage conversion resistor 25, and the flow voltage is measured. Thus, the flow rate of the fluid flowing through the pipe 1 can be obtained.

In this prior art, power is supplied to the arithmetic circuit 6 through a power supply line 23 and a current detection line 24, and a flow current F (flow voltage ), Which constitutes a so-called two-wire type flow meter.

By the way, in a flow meter, the transmitter / receivers 3 and 4 are generally connected to a metal tube 1 (for example, in the above-mentioned prior art, each of the tubes 1 and the first transmitter / receivers 3 and 4 is connected). Electrodes 3a and 4a). Therefore, the flow meter must be
When configured as a wire system, the transmission and reception
When the first electrodes 3a and 4a of the receivers 3 and 4 are electrically connected to the tube 1, for example, as shown in FIG. The current flows from the power source 22 to the current detection side line 24 because the current flows from the power supply 22 to the current detection side line 24 through the circuit 6, the transmitter / receivers 3 and 4, and the tube 1 to the ground (ground) side. Can no longer be measured.

In the case where the flow meter is configured as a two-wire system, the above-described problem may be caused. On the other hand, the above-described prior art shown in FIG. 4 insulates the main operation unit 6a from the sub operation unit 6b. DC / DC converter 12 and photocoupler 4
0 is provided to ensure the flow of the flow current F indicating the flow rate of the fluid to the current detection side line 24.

[Problems to be solved by the invention]

However, in the above-mentioned prior art, the switching circuit 18
DC / DC converter 12 having photomask and photocoupler 40
In addition, the DC / DC converter 12 is integrally provided with an insulating transformer 11 in order to prevent the above-mentioned ground fault via the tube 1 and to secure the flow of the flow current F to the current detection side line 24, and Since the filter circuit 14 is provided to remove the noise of the ultrasonic reception signal B output from the receiver 4, the circuit configuration becomes complicated, and the power consumption increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a flow meter having a simple configuration capable of preventing a ground fault via a pipe.

[0014]

SUMMARY OF THE INVENTION The present invention provides two terminals for a pipe through which a fluid flows, a transmitter / receiver attached to the pipe for transmitting and receiving ultrasonic waves through the fluid in the pipe, and a measuring instrument having a power supply. And an arithmetic circuit that is supplied with electric power from the power source, generates a current indicating the flow rate of the fluid based on the sending / receiving signals of the sending / receiving device, and outputs the current to the measuring instrument, and the operating circuit And an insulating transformer interposed between each of the transmitter and the receiver.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A flow meter according to an embodiment of the present invention will be described below with reference to FIGS. FIG.
The same reference numerals are given to members and portions equivalent to the members and portions shown in (1) and the description thereof is omitted as appropriate.

1 and 2, the arithmetic circuit 6 includes an oscillation circuit 8, a phase comparison circuit 9, a microcomputer circuit 10,
An analog output circuit 17 that receives a flow signal D from the microcomputer circuit 10 and generates a current (flow current F) indicating the flow rate of the fluid, and a voltage (24 V) of a power supply 22 provided in the measuring instrument 7
To a predetermined voltage (5V), a DC / DC converter 12, a waveform shaping circuit 16 interposed between the receiver 4 and the phase comparator 9, and an oscillator 8 and the transmitter 3. It is roughly composed of insulating transformers 11 (referred to as transmitting and receiving insulating transformers 11A and 11B, respectively) interposed between the waveform shaping circuit 16 and the receiver 4. The analog output circuit 17 has a DC / DC converter 1
2 are connected and supplied with electric power. The phase comparison circuit 9 is connected to the DC / DC converter 12 so as to form a closed circuit. The microcomputer circuit 10 is also D
It is connected to the C / DC converter 12 so as to form a closed circuit.

The isolation transformers 11A, 1 on the transmission side and the reception side
1B, a current flows through the secondary coil 11b due to a magnetic field change generated by the primary coil 11a, while the primary coil 11a and the secondary coil 11b are electrically insulated. Transmitter-side and receiver-side isolation transformers 11
A and 11B have a turns ratio of a value exceeding “1” and have a boosting function.

One terminal T _Aa1 of the primary coil 11a of the transmitting side insulation transformer 11A is connected to the oscillation circuit 8,
The other terminal T _Aa2 is connected to a common terminal 12T of the DC / DC converter 12 (common potential of the entire operation circuit 6). Secondary coil 1 of insulating transformer 11A on the transmission side
One terminal T _Ab1 of 1b is connected to a first electrode 3a of the transmitter 3, the other terminal T _Ab2 second electrode 3 of the transmitter 3
b.

One terminal T _Ba1 of the primary side coil 11a of the insulating transformer 11B on the receiving side is connected to the first electrode 4 of the receiver 4.
a, and the other terminal T _Ba2 is connected to the second electrode 4 b of the receiver 4. Isolation transformer 11B on the receiving side
One terminal T _Bb1 of the secondary coil 11b is connected to the input terminal of the waveform shaping circuit 16, and the other terminal T _Bb2 is
/ DC converter 12 is connected to common terminal 12T.

The isolation transformers 11A, 1 on the transmission side and the reception side
The impedance of 1B is set to a predetermined value. A resonance system is formed by the transmission-side and reception-side insulation transformers 11A and 11B and the ultrasonic sensor 5 (transmitter / receiver 3 and 4), and the transmission-side and reception-side insulation transformers 11A and 11B are formed.
The desired resonance frequency is obtained by the impedance value of, and the required signal is efficiently extracted. Here, when the transmitter 3 of the transmitter / receivers 3 and 4 is represented by an electrical equivalent circuit by way of example, the result is as shown in FIG. That is, a circuit (equivalent circuit) 30 is shown in which the capacitor C ₁ , the resistor R and the coil L are connected in series, and the capacitor C ₂ is connected in parallel to this series connection. The secondary coil 11b of the transmitting-side insulating transformer 11A is connected to the circuit 30. The receiver 4 includes a primary-side coil 11 of a receiving-side insulating transformer 11B.
a is connected. A resonance system is formed by the transmitter / receivers 3, 4 and the transmission and reception side isolation transformers 11A, 11B. As described above, resonance is achieved by changing each coil 11a, 11b to a coil having a different inductance (impedance). The frequency can be adjusted.

The impedance characteristics of the transmitters / receivers 3 and 4 change with temperature. When the flowmeter is used over a wide temperature range, the ultrasonic transmission characteristics may be reduced in a certain temperature range. In particular, if the transmission efficiency of ultrasonic waves is set to be good at normal temperature, transmission transmission characteristics may be reduced in a high temperature region or a low temperature region within the operating temperature range. In the present embodiment, the above-described setting of the resonance frequency is performed by the transmitter / receiver 3, which changes within the operating temperature range.
The measurement is performed with the center value of the impedance change width of the impedance characteristic of No.

In the present embodiment, the impedance of the transformers (11A, 11B) follows as the resonance frequency of the ultrasonic sensors (transmitter / receiver 3, 4) changes depending on the temperature (that is, the impedance of the transformer (11A, 11B) follows). The impedance (resonance system) of the ultrasonic sensor and transformer changes with temperature,
(Transformer whose impedance changes equivalently to the impedance-temperature characteristic of the ultrasonic sensor) is selected, whereby the reduction in efficiency due to the difference between the impedance of the ultrasonic sensor and the impedance of the transformer can be suppressed, and any temperature range Thus, stable transmission and reception of ultrasonic waves can be achieved.

In the flow meter configured as described above, the waveform shaping circuit 16 and the receiver 4 are connected between the oscillator 8 and the transmitter 3.
Between the transmission side and the reception side, respectively.
As shown in FIG. 2, the current from the power supply 22 provided in the measuring instrument 7 flows to the current detection side line 24 because A and 11B are interposed. Therefore, a ground fault occurring in the flow meter of FIG. 5 [a phenomenon in which a current from the power supply 22 flows to the ground (ground) side via the power supply line 23, the arithmetic circuit 6, the transmitters / receivers 3, 4 and the pipe 1] Never invite.

In the prior art shown in FIG. 4 described above, a ground fault via the pipe 1 is prevented, and the flow current F
In order to secure the power supply to the DC / DC converter 12, the DC / DC converter 12 is provided integrally with the insulating transformer 11, and a filter circuit 14 is provided for removing noise of the ultrasonic reception signal B output from the receiver 4. Further, the provision of the photocoupler 40 complicates the circuit configuration, thereby increasing the power consumption. On the other hand, in the present embodiment,
The above-described ground fault prevention is performed by the insulating transformers 11A and 11B, and the transmitting and receiving insulating transformers 11A and 11B are used.
B is set to a predetermined value, a desired resonance frequency is obtained by the impedance values of the isolation transformers 11A and 11B on the transmission side and the reception side, and necessary signals are efficiently extracted. By removing the noise generated by impact or the like on the filter 4, the filter circuit 14 required for the flow meter of FIG. 4 can be omitted, and as a result, the configuration of the entire circuit can be simplified and the consumption can be reduced. Current can be suppressed.

Further, since the resonance frequency is set by the center value of the impedance change width of the impedance characteristics of the transmitter / receivers 3 and 4 which changes within the operating temperature range, the ultrasonic transmission is stable over a wide range within the operating temperature range. Transfer characteristics can be obtained.

The transmitting and receiving insulating transformers 11A, 11A
1B has a turns ratio of a value exceeding "1" and has a boosting function, so that the amplifier circuit 15 required in the prior art of FIG. 4 can be omitted, and the device configuration can be simplified accordingly. it can.

As described above, in the present embodiment, between the oscillation circuit 8 and the transmitter 3, the waveform shaping circuit 16 and the receiver 4
Between the transmission side and the reception side, respectively.
By interposing A and 11B, an insulation function is exhibited to prevent the occurrence of a ground fault phenomenon via the pipe 1 which occurs in the flow meter of FIG. 5, and the insulation required by the flow meter of FIG. While the complicated DC / DC converter 12 having the transformer 11 and the photocoupler 40 can be omitted, the insulating transformer 1
1 performs a filter function and an amplifier function, and a filter circuit 14 and an amplifier circuit 15 required for the flow meter of FIG.
Is omitted, so that the device configuration can be greatly simplified.

In the above embodiment, the case where the flow meter is an ultrasonic vortex flow meter is described as an example, but the present invention is not limited to this.
As long as the flow meter has an ultrasonic sensor, another type of flow meter that does not use Karman vortex may be used.

In the above embodiment, the insulating transformer 11
Although the case where A and 11B have a boosting function has been described as an example, an insulating transformer having no boosting function with a turns ratio of “1” may be used.

In the prior art shown in FIG. 4 described above, the insulating transformer 11 is provided near the power supply 22, so that the current in the insulating portion is large and the current loss due to the insulating transformer is correspondingly large. However, in the present embodiment, the current flowing through the power supply 22 is small, and the current flowing between the arithmetic circuit 6 and each of the transmitters / receivers 3 and 4 may be reduced. Are provided with the isolation transformers 11A and 11B, the current loss due to the insulation transformer can be suppressed to the minimum necessary, and the occurrence of the above-described problem can be reliably prevented.

[0031]

According to the present invention, an insulating transformer is interposed between the arithmetic circuit and each of the transmitter and the receiver. The insulating transformer exhibits an insulating function, and the transmitter and the receiver are connected to each other via a pipe. In addition, a resonance system is formed by the isolation transformer and the transmitter / receiver, and the resonance frequency of the resonance system can be adjusted by setting the impedance of the insulation transformer. , The required signal is efficiently extracted, and the noise generated by the impact on the transmitter / receiver or the like can be removed (that is, the insulating transformer also functions as a filter). Therefore,
The isolation transformer and photocoupler required to prevent ground faults in the conventional technology, and the filter circuit required to eliminate noise, were replaced with only the isolation transformer provided between the arithmetic circuit and the transmitter / receiver. Can be replaced, resulting in
The configuration of the entire circuit can be further simplified, and current consumption can be suppressed.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram for explaining the operation of the flow meter of FIG.

FIG. 3 is a diagram showing an electrical equivalent circuit of a transmitter (receiver).

FIG. 4 is a diagram schematically showing an example of a conventional flow meter.

FIG. 5 is a schematic diagram showing a ground fault that can occur in a flowmeter without insulation.

[Explanation of symbols]

 3 Transmitter 4 Receiver 6 Arithmetic circuit 11A Insulation transformer on the transmission side 11B Insulation transformer on the reception side

Claims (1)

[Claims] 1. A pipe through which a fluid flows, a transmitter / receiver attached to the pipe for transmitting and receiving ultrasonic waves through the fluid in the pipe, and a measuring instrument having a power supply connected via two terminals to the power supply. An arithmetic circuit which is supplied with electric power and generates a current indicating the flow rate of the fluid based on the send / receive signals of the send / receiver and outputs the current to the measuring instrument; and each of the arithmetic circuit and the send / receiver And an insulating transformer interposed between the flowmeter and the flowmeter.