KR960014000B1 - Pressure sensor structure and circuit - Google Patents

Abstract

The circuit of metallic thin film pressure sensor comprises : a constant voltage-supplying part(1) comprising a transformer(TS), a bridge diode(BD) and two regulators, and supplying constant voltage to a sensor(Sen) and an op-amp(U); an amplifying circuit(3) for performing two-step amplification of differential voltage detected from the measuring sensor(Sen); an offset controlling circuit for setting the bridge non-equilibrium voltage to "0" volt with a variable resistor(VR); a comparator for comparing the amplified voltage of the amplifying circuit with a reference voltage of the offset circuit; a relay(Ry) and a TRIAC which are turned ON or OFF by the output of the comparator; and the analog signal of the comparator is displayed by using a double-integration A/D converter(IC1).

Description

Metal Thin Film Pressure Sensor Structure and Its Circuits

1 is a diagram for explaining the present invention.

2 is a circuit diagram of an embodiment of the present invention;

(a) is a constant voltage supply circuit

(b) is a measuring sensor circuit and amplification and offset adjustment circuit.

(c) shows the relay driving circuit by the reference voltage buffer circuit and the comparison circuit.

(d) triac driving circuit

(e) means the display circuit,

3 is a structural diagram of the integrated housing of the pressure sensor.

4 is an explanatory view of a housing structure of an embodiment of the present invention;

(a) is sectional drawing for housing description.

(b) is sectional drawing of a diaphragm.

* Explanation of symbols for main parts of the drawings

1: constant voltage supply part 2: measurement sensor part

3: amplifying section 4: digital display section

5: pressure switch TS: transformer

BD: Bridge Diode C1-C4: Capacitor

Reg: Regulator Sen: Sensor

U1-U4: OP amp Ry: Relay

TRIAC: Triac IC1: Dual Integral A / D Converter

IC2: 7-segment display Lead: Load

VR1, VR2: Variable resistor a: Housing

b: diagram c: strain gauge

d: middle ped e: electric circuit board

f: variable resistor g: amplifier

h: lead wire.

The present invention relates to a metal thin film pressure sensor and a novel circuit thereof, and more particularly to a strain gauge type metal thin film pressure sensor.

It is already known that a stainless diaphragm type metal foil pressure sensor can measure pressure even in harsh environmental conditions, and according to Japanese Patent Laid-Open No. 4-265831, it is not necessary to connect a separate temperature sensor or a special sensor. In addition, a simple analog temperature compensation circuit method for resistance bridges is provided with a voltage-controlled current source that provides an output current proportional to the reference voltage to the resistance bridge, and the buffer amplifier generates a buffer output current proportional to the output current described above. Generates an initial output that is proportional to the response that is output so that the programmable gain amplifier produces a compensated output independent of the bridge's pressure response, and the gain compensation portion of the compensation network compensates for variations in the bridge response to offset offset. Initial offset current in response to the additional buffer output voltage To the production so as to be offset correction amplifier to generate a correction signal.

However, such a measurement circuit in the conventional pressure sensor has a complicated problem in adjusting the offset voltage of the sensor signal and the gain of the amplification circuit, and it is inconvenient to assemble because it is necessary to attach four sensors to the sensing plate. There is a problem that the rate of occurrence is high.

The present invention is to solve the conventional problems as described above, it is simple to perform the offset adjustment and gain adjustment of the amplifier circuit and the amplifier function with one of the quid operation amplifier, simple, easy to assemble and inexpensive and economical Furthermore, using a quip op amp for buffers and comparators, a pressure switch can be used to turn the relay on and off within a desired value, and one analog digital converter can display the measured pressure digitally.

In addition, the measuring sensor achieves the object by allowing the strain gauge to be a resistance of a metal thin film such as cons vantan.

In other words, the measuring sensor is bonded on the stainless steel diaphragm under pressure, and this diaphragm is placed on the blowing part where the gain is received. When the measuring sensor is pressurized, the resistance of the measuring sensor changes in proportion to the bending by the pressure. I did it.

Therefore, the SUS304 or SUS606 series of housings and diaphragms can be used to measure under adverse environmental conditions.

That is, in the conventional silicon, not only compensation for temperature change is required but also it cannot be used for toxic and corrosive gases or liquids. However, in the present invention, it is possible to use in a harsh environment by using a stainless steel diaphragm. Its excellent temperature elimination is not required and its long-term stability makes it economical.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram of the circuit part of the present invention, and supplies an operating current to each circuit from the constant voltage supply part 1, and the signal sensed by the measuring sensor part 2 is amplified by the amplification part 3 and the digital display part 4. And the pressure switch unit 5 is configured to operate.

FIG. 2 is a circuit diagram of the constant voltage supply unit 1 shown in FIG. 1, and a bridge diode BD is connected to a secondary side of a transformer TS to which primary AC power is applied, and a transformer TS is connected to an output side thereof. Smoothing capacitors (C1, C2) are connected between the secondary terminal of the secondary side, and constant voltage is output to the output terminal (+ Vin) (-Vin) through the regulators (Reg1, Reg2) that are constant voltage elements. It is known to supply power to the circuit. In FIG. 2A, C3 and C4 mean capacitors.

Second (b) shows a circuit diagram for offset adjustment by amplifying the signal sensed by the sensor in one stage and then again in two stages.

That is, the output of the sensor Sen is connected to the inverting terminals (+) of the first stage amplification op amps U1 and U2, and the output of the op amps U1 and U2 is amplified in two stages through the resistors R4 and R5. It is input to the op amp U4, and the inverting terminal (+) of the offset adjustment op amp U3 is controlled through the variable resistor VR so that the bridge unbalance voltage is adjusted to zero. It is fed back to the non-inverting terminal (-) and is connected to the inverting terminal (+) of the op amp (U4) through the resistor (R6). In FIG. 2 (b), the symbols R1-R3, R5, and R7 denote resistances, and the output Vol of the op amp U4 of FIG. 2 (b) is shown in FIG. The non-inverting terminal (-) of the comparator U6 of the relay drive circuit by the reference voltage buffer circuit and the comparison circuit is connected to each other to form a buffer circuit using hysteresis characteristics by comparing the amplified voltage with the reference voltage.

That is, the buffer amp U5 for supplying the reference voltage of the comparator U6 is provided, the reference voltage is adjusted and supplied by the variable resistor VR2, and the output of the comparator U6 is the resistor R11. To the base of the emitter grounded transistor (Q1) and at the same time a light emitting diode (LED) connected between grounds to indicate the operation and to trigger the gate of the triac (TRIAC) through transistor (Q2). It is also possible to control the load (LOAD) connected between the AC power source (AC) and the triac (TRIAC).

FIG. 2E shows the output of the comparator U6 by the 7-segment display IC2 through the dual-integrated A / D converter IC1. The bridge output at is given by the following equation (1).

Vol = KεVin... … … … … … … … … … … … … … … … … … … … … … (One)

Where Vin is the bridge voltage, or a variation, K is the gauge rate, and Vo1 is the bridge differential output voltage.

The output voltage of the amplifier circuit is shown in the following equation (2).

Vo2 = G1 G2 (E2-E1) + Voff... … … … … … … … … … … … … … … … … (2)

G1 = 1 + (2R2 / R1) or 1+ (2R3 / R1)

G2 = R6 / R5

The gain is adjusted by the resistor R1, and the offset is adjusted by the variable resistor VR.

In addition, the equation for setting the desired pressure range of the switch is as shown in the following equation (3) (4).

Where Vut is the voltage at which the pressure switch is OFF

V1t is the voltage at which the pressure switch is turned on

n = R13 / R11

Vr = (Vin + R12) / (R11 + R12)

+ Vsat is opamp + Saturation voltage

-Vsat is opamp-Saturation Voltage

That is, until the output voltage Vo1dl Vut of the amplifier circuit becomes the output voltage (+ Vsat) of the comparator U6, current flows into the base of the transistor Q1, the transistor Q1 operates, and the current flows into the collector. When the relay Ry is turned on and Vut is reached, the output voltage of the comparator U6 becomes (-Vsat) and the transistor Q1 does not operate so that the relay Ry is turned off.

In this OFF state, when the input becomes low and Vo1 becomes V1t, the relay Ry is turned on. TRIAC is driven on the same principle.

In addition, the 7-segment (IC2) for digital display of pressure using the dual integral type A / D converter (IC1) converts the output voltage Vo1 of the amplifying circuit having the analog output value to the A / D converter (IC1) and the resistor. And it becomes possible to display digitally using a capacitor | condenser.

The value to be displayed is given by the following equation (5).

On the other hand, the housing of the pressure sensor may be integrated as shown in FIG. 3 or assembled as shown in FIG.

However, since the integral type as shown in FIG. 3 is made integrally by using SUS304 or SUS606, it can be used even in a poor environment, while it is stable, and the diaphragm thickness of 0.5t or less, for example, is difficult and expensive. There is a disadvantage that can not be used by mounting on the high pressure.

On the other hand, as shown in FIG. 4, the prefabricated type is made of SUS304 or SUS606 in two stages as shown in FIGS. 4A and 4B, respectively, so that the diaphragm b of frame (b) becomes the frame of (a). The strain gauge C of (a) can be screwed into the end to which it fits.

Therefore, when the assembly type as shown in FIG. 4 is used, the diaphragm b can be manufactured and assembled separately, so that the thickness can be processed up to 0.1t, and thus it can be used for the low pressure part.

5 is another embodiment of the present invention, the diaphragm (b) is installed in the housing (a) and the strain gauge (c) is attached to the pressure change to cause a change in resistance, the strain gauge (c) is broken Connect and fix the connection line by using an intermediate pad (d) so that the electronic circuit board (e) has a variable resistor (f) for zero adjustment and an amplification part (g) for amplifying the output signal of the pressure sensor. The power supply is supplied to the lead wire h, and the variable resistor f can be adjusted from the outside by drilling a hole j in a portion where the variable resistor f is located in the housing a. .

Since the strain gauge (c) is fixed to the diaphragm (b) as described above, as well as workability and economical efficiency, assembling is easy and adjustment is convenient.

Claims (3)

The differential voltage detected by the above-described measuring sensor (Sen) is constituted by constructing a constant voltage supply unit (1) for supplying a stable constant voltage by a transformer, a bridge diode, and a regulator. An amplification circuit for amplifying the voltage by two stages with a quid operation amplifier and an offset adjustment circuit for zero-volt bridge unbalance with a variable resistor (VR), the reference being the amplified voltage of the amplifying circuit and the total power of the offset circuit. Comprising a comparator for comparing the voltage and the output of the comparator to turn on or off the relay or triac, characterized in that to display the analog signal of the comparator using a dual integral A / D converter Circuit of metal thin film type pressure sensor. The diaphragm (b) is installed in the housing (a), the strain gauge (c) is attached to the diaphragm (b), the connection line is connected and fixed to the strain gauge (c) through the intermediate pad (d) And the zero point variable resistor f and the amplifying part g are fixed to the electronic circuit board e, and the housing a is perforated in the hole j in the position where the variable resistor f is located. Structure of a metal thin film type pressure sensor, characterized in that the variable resistor (f) can be adjusted from the outside. The structure of a metal thin film pressure sensor according to claim 2, wherein the housing (a) can be assembled in two stages, and the diaphragm (b) is installed in the housing (a).