JPH07110275A - Pressure sensor circuit - Google Patents

Abstract

PURPOSE:To provide a pressure sensor circuit which is hardly affected by noise. CONSTITUTION:In a pressure sensor circuit composed of a bridge circuit 29 incorporating a strain gauge 2 for detecting pressure, a measuring amplifier 7 for amplifying the output voltage of the circuit 29, and a current amplifier 8 for amplifying the current in the output of the amplifier 7, a power source section (21) which supplies electric power to each section is constituted in an insulating state so as to prevent the pressure sensor circuit from being hardly affected by noise and improved in measuring accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor (hereinafter also referred to as a pressure sensor circuit) incorporating an electronic control circuit, and more particularly to an improvement thereof.

[0002]

2. Description of the Related Art FIG. 5 is a sectional view showing a conventional example of a pressure sensor device. That is, in a cylindrical case 4 made of steel or stainless steel, a diaphragm 1 that receives a pressure and a strain gauge 2 attached to the diaphragm 1
And an electronic circuit 3 and the like. That is, the chamber that responds to the pressure and the chamber that houses the electronic circuit 3 are separated by the diaphragm 1. The diaphragm 1 is deformed when pressure is applied, and the strain gauge 2 attached to the diaphragm 1 is correspondingly distorted to change its resistance value, and this is taken out as a pressure signal. In addition, 5 is an electric wire and 6 is a bush.

By the way, since the change of the strain gauge 2 is minute, when the influence of external noise is exerted, the change in pressure cannot be detected on the receiving side. Therefore, usually, an electronic circuit is provided for converting this strain gauge change into an electric signal and amplifying it. FIG. 6 shows a specific example thereof.

The pressure sensor circuit is the strain gauge 2 described above.
Measuring bridge 29 composed of a resistor for converting the distortion of the electric field into an electric change, and a measuring amplifier 7 for amplifying the change.
And a current amplifier 8 for outputting to the outside, a constant voltage power supply circuit 9 for supplying a stable power supply to them, and the like. As described above, the signal is output as a current signal (4 to 20 mA) in order to reduce the influence of external noise on the outside.

Now, the resistance value of the strain gauge 2 shown in FIG. 6 is R1, and the other resistance values of the measuring bridge 29 are R2 and R.
3, R4, and assuming that the voltage applied to the measurement bridge 29 is ei, the voltage e output from this bridge 29
Is e =-(R1R2-R3R4) / {(R1 + R4) (R2 + R3)}. Ei (1).

Here, the resistance values R2 and R in the equation (1)
If R3 and R4 are set to the same value as R1, (R2 = R3 = R4 =
R1), the voltage output e becomes zero when no pressure is applied. On the other hand, if the strain gauge 2 is distorted under pressure and the resistance value becomes R1 + ΔR, the voltage output e
Becomes e =-{ΔRR1 / (4R1 ² + 2R1ΔR)} ei (2).

Since R1 >> ΔR in general, the above equation (2) can be approximated as e = −ΔRei / 4R1 (3). Therefore, assuming that the amplification degree of the measurement amplifier 7 in FIG. 6 is k, the output Eout of the measurement amplifier 7 is Eout = −kΔRei / 4R1 (4), which is converted into a current amount by the current amplifier 8 and externally output. Is output to.

FIG. 7 shows a concrete example of FIG. Here, the measurement amplifier includes a differential amplifier 10 including an operational amplifier (op amp), and the current amplifier includes an inverting amplifier 11 including an operational amplifier, an output transistor 12 for current amplification, an internal reference load 13, and the like. Here, the internal reference load 13 is, for example, 250 when the output is 4 to 20 mA.
Ω is selected, and the voltage drop (1 to 5 V) here is fed back to the inverting amplifier 11 for current adjustment.

The constant voltage power supply is composed of an output transistor 15, a voltage control transistor 16 and a constant voltage diode 17 here, and the voltage control transistor is controlled so that the output voltage of the output transistor 15 becomes equal to the voltage of the constant voltage diode 17. 16 controls the base current of the output transistor 15 to adjust the output voltage. A well-known one can be used as such a constant voltage power supply. Reference numeral 14 in FIG. 7 indicates a load (RL), 18 indicates a power supply terminal, 19 indicates an output terminal, and 20 indicates an external receiving amplifier.

[0010]

As described above, the pressure sensor circuit is of a compact structure because it is housed in the cylindrical case as shown in FIG. 5, and is of a non-insulated type which has a simple circuit structure for cost reduction. I am trying. However,
In the case of such a non-insulated type, if external noise enters, it propagates in the circuit and adversely affects it. For example, GIS (Gas Insulated Switchc)
The gas pressure sensor used for the purpose of monitoring the gas pressure, such as hGear), G-GIS, or gas-insulated cubicle, is often placed in a severe electromagnetic environment such as a substation and therefore has a bad noise environment. It is easily affected.

The location where noise invades is the power supply terminal 18 or the output terminal 19 in FIG. 7, and if noise intrudes from there and the internal power supply fluctuates by Δe, the output Eout of the measurement amplifier is Eout =- It becomes kΔR (ei ± Δe) / 4R1 (5) and fluctuates by ± kΔRΔe / 4R1, and this is converted into current and output. The amplification factor k of the measurement amplifier is very large, so when affected by noise,
This causes a problem that this is greatly amplified and output. Therefore, an object of the present invention is to prevent the invasion and propagation of noise and improve the accuracy.

[0012]

In order to solve such a problem, according to the first invention, a pressure sensor section for detecting a pressure change, a first amplifying circuit for amplifying the output of the pressure sensor section, and an output thereof are provided. In a pressure sensor circuit comprising a second amplification circuit for current amplification and a power supply section for supplying power to the pressure sensor section and the first and second amplification circuits, the power supply section is an insulated power supply section. It is characterized by doing.

According to a second aspect of the present invention, a pressure sensor section for detecting a pressure change, a first amplifying circuit for amplifying its output by voltage, a second amplifying circuit for amplifying its output by current, the pressure sensor section, and In a pressure sensor circuit having a power supply section for supplying electric power to the first and second amplification circuits, the power supply section is of an insulating type, and a dual output type is provided for the first amplification circuit and the second amplification circuit. It is characterized in that power is supplied individually and an insulating amplifier is inserted between the first amplifier circuit and the second amplifier circuit.

[0014]

[Action]

(1) The power source of the pressure sensor circuit is an insulated type. (2) Insulate the power supply of the pressure sensor circuit and
As an output type, power is supplied individually to the voltage amplification section and the current amplification section, and an isolation amplifier is inserted between the voltage amplification section and the current amplification section. By setting either of the above, the influence of noise is extremely reduced and the measurement accuracy is improved.

[0015]

1 is a schematic diagram showing an embodiment of the present invention, FIG.
Is a detailed circuit diagram thereof. This embodiment is roughly constructed as shown in FIG. As is clear from the figure, the feature is that the power source is configured by the insulated power source 21 so that noise is not superimposed on the power source applied to the bridge 29. In this way, it is effective not only for normal mode noise coming between the lines of the power supply terminal 18 but also for common mode noise, that is, common mode noise.

The insulating power source 21 is specifically composed of a switching transistor 22, an insulating transformer 23, a rectifying diode 24, a voltage control circuit 25, etc., as shown in FIG. The insulated power supply 21 is generally well known as a switching power supply.

That is, while the transformer 23 is used for insulation, the voltage control circuit 25 monitors the power supply voltage,
Switching transistor 22 so that this becomes constant
The constant voltage is maintained by controlling the gate of the. The diode 24 is used as a rectifier. Moreover, if a noise filter or the like is added to the output stage, the noise removing effect is further enhanced.

FIG. 3 is a schematic diagram showing another embodiment of the present invention. Since noise may enter not only from the power supply terminal but also from the output terminal, the insulating amplifier 26 is inserted between the measurement amplifier 7 and the current amplifier 8 in order to cope with such a case. Together with the measurement bridge 29
Also, the power supply to the measurement amplifier 7 and the power supply to the current amplifier 8 are separated, and a two-output power supply 27 is used to reduce mutual influence.

A detailed circuit diagram of the dual output power supply 27 is shown in FIG. That is, the isolation amplifier 26 is installed between the differential amplifier 10 and the inverting amplifier 11 to insulate the measurement side from the output side and prevent noise from entering from the output terminal 19 side.
The power supply unit is composed of a two-output isolation transformer 28 having two outputs each insulated on the output side, a switching transistor 22, a rectifying diode 24 and a voltage control circuit 25 which are independent of each other. The details are omitted because it is the same as FIG. 2 except that the transformer 28 has two outputs.

By doing so, the measuring section (bridge and measuring amplifier) is completely shielded from noise. However, although the current amplifier side is still exposed to noise even in this way, the amplification degree of the amplifier is considerably smaller than that of the measurement amplifier, and the output is a current type that is not easily affected by noise. Therefore, it is not necessary to consider the influence of noise.

[0021]

As described above, according to the present invention, the power source section is of the insulating type, so that the influence of noise can be reduced and the measurement accuracy can be improved. Therefore, this invention is GIS, G-GIS
Alternatively, if the present invention is applied to a gas pressure sensor such as a gas-insulated cubicle that must be used in a place where the noise environment is extremely bad, the effect will be greater.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is a detailed view of FIG.

FIG. 3 is a schematic view showing another embodiment of the present invention.

FIG. 4 is a detailed view of FIG.

FIG. 5 is a cross-sectional view showing a conventional example of a pressure sensor device.

FIG. 6 is a schematic diagram showing a conventional example of a pressure sensor circuit.

FIG. 7 is a detailed view of FIG.

[Explanation of symbols]

1 ... Diaphragm, 2 ... Strain gauge, 3 ... Electronic circuit, 4 ... Case, 5 ... Electric wire, 6 ... Bush, 7 ... Measurement amplifier, 8 ... Current amplifier, 9 ... Constant voltage power supply, 10 ... Differential amplifier, 11 ... Inversion amplifier, 12 ... Output transistor, 1
3 ... Reference load, 14 ... Load (RL), 15 ... Power supply output transistor, 16 ... Voltage control transistor, 17 ... Constant voltage diode, 18 ... Power supply terminal, 19 ... Output terminal, 20
External reception amplifier, 21 ... Insulated power supply, 22 ... Switching transistor, 23 ... Isolation transformer, 24 ... Rectifier diode, 25 ... Voltage control circuit, 26 ... Isolation amplifier, 27
… 2-output isolated power supply, 28… 2-output isolated transformer, 29…
Measurement bridge.

Claims (2)

[Claims] 1. A pressure sensor unit for detecting a pressure change, a first amplifier circuit for amplifying the output of the pressure sensor, a second amplifier circuit for amplifying the output of the current with a current, the pressure sensor unit and the first and first pressure circuits. 2. A pressure sensor circuit having a power supply section for supplying electric power to an amplifier circuit, wherein the power supply section is an insulated power supply section. 2. A pressure sensor section for detecting a pressure change, a first amplification circuit for amplifying the output of the pressure sensor by a voltage, a second amplification circuit for amplifying the output of the current with a current, the pressure sensor section, and the first and the first circuits. A pressure sensor circuit having a power supply section for supplying power to two amplifier circuits, wherein the power supply section is an insulating type, and the first output circuit and the second supply circuit are individually supplied with power as two output types. The pressure sensor circuit according to claim 1, wherein an insulation amplifier is inserted between the first amplification circuit and the second amplification circuit.