JP2570391Y2 - Pressure sensor circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor circuit for detecting the capacitance of a capacitance-change type pressure sensor.

[0002]

2. Description of the Related Art Conventionally, a general pressure sensor circuit 20 of this type includes a timer IC 11, two resistors 12, 13 and a capacitor 14 for preventing malfunction, as shown in FIG.
And a capacitor 2 whose capacitance changes in response to a change in pressure, so that its oscillation cycle or oscillation frequency can be detected.

[0003]

An invention is to you'll solve]] The In the conventional pressure sensor circuit, such as, the electrostatic capacitance of the capacitor 2 and C _1, the resistance value of the resistor 12 and R _3, the resistance value of the resistor 13 Is R ₄ , the oscillation period T is

## EQU1 ## It is expressed as T = ln2 · (R ₃ + R ₄ ) · C ₁ . However, since the capacitance C ₁ of the capacitor 2 generally has a temperature characteristic, the capacitance changes according to the temperature. Since the IC 11 itself has a temperature characteristic, it is difficult to detect the pressure with high accuracy. When the capacitance of the capacitor 2 changes by ΔC due to pressure, the change ΔT of the oscillation cycle becomes

## EQU2 ## ΔT = ln2 · (R ₃ + R ₄ ) · ΔC However, when used as a sensor, it is easy to use that a change corresponding to the pressure of ΔT appears with the reference being 0. When the reference is not 0, it is sufficient that the reference is always a fixed known value. However, in the case of the conventional product, the reference varies depending on variations in C ₁ , R ₁ , R ₂ and the timer IC 11, and is applied as a sensor. Had many disadvantages.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a capacitor for determining output pulses of two one-shot multivibrators is provided with a capacitance by pressure. Of the two one-shot multivibrators by using a capacitor that changes in temperature and a capacitor for temperature compensation, and using each output as an input to the other one-shot multivibrator. Each output is differentially amplified through an integration circuit,
High-precision pressure detection over a wide temperature range enables the offset caused by the temperature characteristics of the capacitor, the capacitance of which varies with pressure, and the errors due to the resistance and IC to be eliminated, and the reference point to be easily set to zero. The aim is to obtain a possible pressure sensor circuit.

That is, the pressure sensor circuit according to the present invention comprises a one-shot multivibrator 3 having a time constant portion including a resistor 1 and a capacitor 2 whose capacitance changes according to pressure.
Is used as a trigger input of a one-shot multivibrator 7 having a resistor 4, a variable resistor 5, and a temperature compensating capacitor 6 for compensating the temperature characteristics of the capacitor 2 in a time constant section. An output of the vibrator 7 is used as an input to the one-shot multivibrator 3 to constitute an astable multivibrator, and an output of each of the one-shot multivibrator 3 and the one-shot multivibrator 7 is integrated by an integrating circuit 8.
And an integrating circuit 9 are provided, and the integrated voltages of the two integrating circuits are amplified by a differential amplifier 10.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a pressure sensor circuit of the present invention. A one-shot multivibrator 3 includes a resistor 1 and a capacitor 2 whose capacitance changes according to pressure in a time constant section. The other one-shot multivibrator 7 has a resistor 4, a variable resistor 5, and a temperature compensating capacitor 6 for compensating the temperature characteristics of the capacitor 2 in a time constant portion.
And The output of the one-shot multivibrator 3 is used as a trigger input of the other one-shot multivibrator 7 and the output of the one-shot multivibrator 7 is used as an input of the one-shot multivibrator 3. It constitutes an astable multivibrator. The one-shot multivibrator 3 and the one-shot multivibrator
Each output of the multivibrator 7 is connected to an integrating circuit 8 and an integrating circuit 9, and the integrated voltages of these integrating circuits are amplified by a differential amplifier 10.

[0007]

The operation of the pressure sensor circuit thus configured will be described with reference to the timing chart of FIG. Resistance 1 of Figure 1, the resistor 4, the resistance value of each of R ₁ of the variable resistor 5,
And R _2, R _X, the capacitor 2, C _S, respectively the capacitance of the capacitor 6, when C _X, the output pulse width T1 of one-shot multivibrator 3 in point A,

Equation 3] _{T1 = K · R 1 · C} S Also, the output pulse width T2 of the one-shot multivibrator 7 at point B,

Equation 4 is a _{T2 = K · (R 2 +} R X) · C X. One-shot multivibrators 3 and 7
Is T1 or T2 depending on the falling edge of the input.
The output of the one-shot multivibrator 3 and the output of the one-shot multivibrator 7 are input to the other one-shot multivibrator, and therefore oscillate at a period of (T1 + T2). It becomes a multivibrator that lasts.

The outputs of the one-shot multivibrator 3 and the one-shot multivibrator 7 are integrated by the integrating circuits 8 and 9, respectively, so that the output voltage of the integrating circuit 8 and the output voltage of the integrating circuit 9 are V1 respectively. , V2,

[Number 5] _{V1 = V H · (T1 /} T1 + T2) V2 = V 'H · (T2 / T1 + T2) here, V _H, V' _H is the voltage at the time of one-shot multivibrator High. Therefore, if V1 and V2 are amplified by the differential amplifier circuit 10 (amplification degree G), the output voltage Vout becomes

[6] Vout = G · (V1 -V2) = G ((V H · T1 -V 'H · T2) / (T1 + T2)) = G ((V H · K · R 1 · C S -V ' _H · K · (R ₂ + R _X ) · C _X ) / (T 1 + T 2)), and Vout is V _H , R ₁ , C _S , V ′ _H , R ₂ , R
Depending on _X and C _X , the following effect can be expected.

That is, the above-mentioned one-shot multivibrator is, for example, 74LS123, 74LS22.
ICs with model numbers of 1,4538 and the like can be used, each having two circuits in one package, and their temperature characteristics and output voltages V _H and V ′ _H have very similar characteristics. Furthermore, if adjusted to Vout = 0 by R _X of the variable resistor 5, the capacitor 2 whose capacitance changes according to the pressure C
Vout changes as _X increases or decreases, making it very easy to use as a pressure sensor. Further, as the C _X capacitor 6, the use of those C _X the same characteristics of the capacitor 2, the temperature to offsetting effect is obtained, it is possible to improve the temperature characteristics of the output voltage. The same applies to the resistor and the one-shot multivibrator, and it can be easily inferred that the characteristics work to offset each other.

[0010]

As described above, according to the present invention, each of the capacitors for determining the output pulses of the two one-shot multivibrators 3 and 7 includes the capacitor 2 whose capacitance changes according to pressure, and the temperature. An astable multivibrator is constructed by using a compensating capacitor 6 and using each output as the input of the other one-shot multivibrator, and integrating the outputs of the two one-shot multivibrators. Since the signal is differentially amplified through a circuit, the action of a one-shot multivibrator having a temperature compensating capacitor 6 in a time constant section causes an error due to a temperature characteristic of a capacitor whose capacitance changes due to pressure, High accuracy pressure over a wide temperature range because errors due to resistance and IC can be offset Out are possible, also easily used as a sensor to increase or decrease the output voltage in response to pressure from the reference point, its practical effects are those large becomes.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a pressure sensor circuit according to the present invention.

FIG. 2 is a circuit diagram of a conventional pressure sensor circuit.

FIG. 3 is a timing chart of the pressure sensor circuit of the present invention.

[Explanation of symbols]

1 Resistance. 2 Capacitor. 3 One-shot multivibrator. 4 Resistance. 5 Variable resistance. 6
Temperature compensation capacitor. 7 One-shot multivibrator. 8 Integrating circuit. 9 Integrator circuit. 10 Differential amplifier. 11 Timer IC. 12 Resistance. 1
3 Resistance. 14 Malfunction prevention capacitor.

Claims (1)

(57) [Scope of request for utility model registration] 1. An output of a one-shot multivibrator 3 having a resistor 1 and a capacitor 2 whose capacitance changes according to pressure in a time constant part is output from a resistor 4, a variable resistor 5, and a temperature characteristic of the capacitor 2. Is used as a trigger input of a one-shot multivibrator 7 having a temperature compensating capacitor 6 as a time constant part, and an output of the one-shot multivibrator 7 is used as an input of the one-shot multivibrator 3 as an input. A multivibrator is constructed, and an integrating circuit 8 and an integrating circuit 9 are provided at the output of each of the one-shot multivibrator 3 and the one-shot multivibrator 7, and the integrated voltages of these two integrating circuits are amplified by the differential amplifier 10. Pressure sensor circuit configured as described above.