JPH03148030A - Pressure measuring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to read pressure simply by providing a single-shot multivibrator circuit whose oscillating frequency is changed with the changes in resistance values of a plurality of strain gages that are arranged on a diaphragm. CONSTITUTION:A diaphragm part 1a is formed on one surface of a silicon chip 1. Gage resistor parts 4 (4a - 4c) are formed on the other surface of the chip 1. Aluminum electrodes 3a - 3e are formed on the side surfaces of the resistor parts 4. The electrodes 3a and 3d, 3c and 3b and 3d and 3e form the electrodes of the electrode parts 4, respectively. The electric circuits form a triangular-wave generating circuit by using resistors R1 - R3 at the resistor parts 4. The +input terminal of an operational amplifier OP5 is grounded through the resistor R1 and connected to one end es of a Zener diode ZD2 through the resistor R2. One end es is connected to the output terminal of the OP5 through the resistor R5 and also connected to the +input terminal of an operation amplifier OP6 through a delay circuit comprising the resistor R3 and a capacitor C. Thus the triangular wave can be generated at an output terminal et of the OP6 in the triangular-wave generating circuit such as this.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a pressure measuring device that measures pressure using a diaphragm type pressure sensor combined with a semiconductor strain gauge.

<Prior Art> As a type of pressure sensor, one using an element (strain gauge) whose resistance changes when strain occurs is commercially available. This pressure sensor has four strain gauges formed on a diaphragm and has a bridge-type circuit configuration, and when pressure is applied, the resistance of the strain gauges changes.

By passing a constant current through the bridge, it is possible to detect changes in voltage due to changes in resistance (see Japanese Patent Publication No. 68-58933).

The strain gauges mentioned above can be made of metal, but those made of semiconductors, which have a large coefficient of change in voltage with respect to pressure, are often used, so below we will assume a pressure sensor using a semiconductor strain gauge. and proceed with the explanation.

A conventional circuit for detecting the above voltage change is shown in Figure 4 (
[Transistor Technology J pp, 470-481゜＾p
ril 1989). Operational amplifier OPI is based on the constant voltage created by resistor RO and Zener diode ZDL.
From this, the optimum value of the current IIN that causes a constant current of 11N to flow through one end c and d of the bridge BD, which is composed of the strain gauge resistors R1-R4, is determined according to the pressure sensor standard. Measure the voltage V between the other two terminals e and f. Note that the variation range of the voltage Vs corresponding to the rated pressure range (the pressure range for which measurement accuracy is compensated) is defined as a span voltage.

Voltage V is amplified by differential amplifier circuit DA.

The differential amplifier circuit DA includes an operational amplifier OP2. OP3, OF
It is composed of 2nd class. The output V a u l of the differential amplifier circuit DA is displayed by a level meter or the like.

<Problems to be Solved by the Invention> The pressure measuring device described above uses a semiconductor with a high temperature coefficient of resistance, so it is possible to read minute pressure changes, but residual stress acting on the diaphragm and chip An offset voltage (a voltage that appears even at a pressure of -0) Vso is always generated due to thermal distortion and stress generated during installation. The value of this offset voltage depends on the structure and standards of the pressure measuring device, but the value of this offset voltage is approximately 10% of the span voltage (for example, the span voltage
00 mV), which is large.

Furthermore, even pressure measuring devices with the same structure and standard have variations.

Therefore, a variable resistor VRI etc. shown in FIG. 3 is provided on the output side or input end (output side in the figure) of the bridge BD,
There is a problem in that it is time-consuming because it is necessary to individually adjust the offset for each pressure measuring device during manufacturing, inspection, etc.

In addition, when reading the voltage V with the voltage reading needle without adjusting the offset, it is possible to force the reading of the voltage v5o at pressure -O to 0 (applying a reset), but the voltage V5 If ゜ exceeds the resettable range of the voltage reading needle, it will not be possible to reset. Also, since there is no offset adjustment, the dynamic range (
(readable pressure fluctuation width) becomes smaller.

The present invention has been made in view of the above problems, and is an adjustment of a pressure measuring device that measures pressure using a diaphragm type pressure sensor combined with a semiconductor strain gauge, which saves the effort of adjustment. The purpose is to provide.

<Means for Solving the Problems> The pressure measuring device of the present invention for achieving the above object has the following features:
A plurality of strain gauges are arranged on a diaphragm, and an astable multi-vibration break circuit is provided in which the oscillation frequency changes according to a change in the resistance value of the plurality of strain gauges.

<Operation> According to the above method, changes in the resistance value of the strain gauge due to pressurization can be captured as changes in the astable multivibrator circuit oscillation frequency, and changes in the pressure applied to the diaphragm can be measured from this frequency change. can.

<Example> Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments.

Figure 1(a) shows three strain gauge resistors R1 to R.
A perspective view showing a pressure measurement pellet using 3, Fig. 1 (b
) is a sectional view taken along line X-X.

The pressure measuring bellet is made by hollowing out one side of a silicon chip 1 cut into a rectangular parallelepiped shape and forming a guyafram part 1a.
is formed. The outer periphery of the diaphragm part 1a is the rim part 1
b.

Three gauge resistance parts 4a to 4c with impurities diffused therein are formed on the other surface of the silicon chip 1, and aluminum electrodes 3a to 3e are formed on the side surfaces of each of the gauge resistance parts 4a to 4c via elongated lead wires, respectively. has been done. Aluminum electrode 3a
, 3d constitute electrodes of the gauge resistance section 4a, aluminum electrodes 3c and 3b constitute electrodes of the gauge resistance section 4b, and aluminum electrodes 3d and 3e constitute electrodes of the gauge resistance section 4c.

What aluminum electrode 3d has in common is the circuit configuration (see Figure 2).
This is because we took into account.

FIG. 2 shows an electrical circuit diagram of a pressure measuring device using the pressure pellet described above. This electric circuit consists of each gauge resistance section 4a.
This is a triangular wave generation circuit using resistors R1 to R3 of ~4C. Note that the resistors R1 to R3 have a characteristic that they all change in the same direction in response to a change in pressure in one direction.

The input terminal of operational amplifier OP5 is grounded through resistor R1, and connected to Zener diode ZD through resistor R2.
It is also connected to one end e5 of 2.

The open end e of the Zener diode ZD2 is connected to the output terminal of the operational amplifier OP5 through a resistor R5, and is also connected to the input terminal of another operational amplifier OP6 through a delay circuit including a resistor R3 and a capacitor C. The input terminal of the operational amplifier OP6 is connected to the output terminal e of the operational amplifier OP6 through a variable resistor VR2. The terminal et is connected to one input terminal of the operational amplifier OP5, divided by resistors RD, R, and connected to one input terminal of the operational amplifier OP6.

According to the triangular wave generation circuit, by using the delay circuit characteristics of the resistor R3 and capacitor C together with the positive feedback effect, a triangular wave can be generated at the output terminal e of the operational amplifier OP8.

The shape of the triangular wave appearing at terminal el is It becomes e+ -2es r (e"'-1)/R3C.

however, r-R3VH2C/(R3-VH2).

From the above equation, it can be seen that when the value of VH2 is made smaller than R3, the exponent becomes positive, and when the value of VH2 is made larger than R3, the exponent becomes negative. Further, if the variable resistor VR2 is adjusted to VH2-R3, a triangular wave that changes linearly will be obtained, and its frequency f will be f -1/4KVR2C. However, K-R1/(RI+R2).

The shape of the above triangular wave is shown in FIG. Waveform e. is VH2
-Linearly changing triangular wave, waveform e when set to R3
, is a triangular wave that changes with a positive index when VH2<R3, and waveform e,2 is a triangular wave that changes with a negative index when VH2>R3.

Here, when no pressure is applied, the resistance values R1, R2, R
Assume that all 3 are equal.

When expressed as R1-R2-R3-R, under conditions where the triangular wave changes linearly, the frequency fO becomes fo -1/2RC.

If the pressure changes and becomes R1-R2-R3 R+ΔR, the frequency fP under pressure is fp=1
/2(R+ΔR) C , which means that the frequency of the waveform has changed due to pressurization.

Therefore, use a frequency counter to read the respective frequencies fo and fp, and the difference Δf-1/2RC-1/
2 (R+ΔR) C−ΔR/2CR2 The applied pressure can be determined. Therefore, there is no need to use a differential amplifier circuit with a complicated configuration like the conventional one.

Furthermore, in the past, offset adjustment was performed so that the applied pressure becomes V, . . . -O when the applied pressure is -0, but this embodiment does not require offset adjustment.

In the above example, if you want to display the applied pressure,
An oscillation circuit with a frequency fo may be prepared, this frequency fO may be compared with a frequency f during pressurization, and the frequency difference Δf may be displayed.

<Effects of the Invention> As described above, according to the pressure measuring device of the present invention, an astable multi-vibrator circuit using a strain gauge as a resistor is provided, and the oscillation frequency of the astable multi-vibrator circuit is controlled by changes in the resistor. By utilizing changes in the pressure, the pressure can be easily read without the need for complicated offset adjustment work.

[Brief explanation of the drawing]

Fig. 1(a) is a perspective view of a pressure measuring pellet used in a pressure measuring device, Fig. 1(b) is a sectional view of the pressure measuring pellet, and Fig. 2 shows an example of an astable multivibration circuit. FIG. 3 is a graph showing a triangular wave generated by the circuit of FIG. 1; FIG. 4 is a circuit diagram of a conventional pressure measuring device. 4a~4C...Strain gauge R1~R3...S]・Rain gauge resistor 0

Claims (1)

[Claims] 1. Combined with semiconductor strain gauge Pressure is measured using a diaphragm pressure sensor. In a pressure measuring device that measures force, Multiple strips placed on the diaphragm train gauge and the above multiple strains. The oscillation frequency changes due to changes in the resistance value of the in-gauge. Astable multivibrator with variable number A pressure circuit comprising: measuring device.