JPS6122766B2 - - Google Patents

Description

[Detailed description of the invention] The present invention is based on the output voltage change (span) with respect to pressure.
This invention relates to a pressure transmitter with temperature compensation.

A conventional general pressure transmitter has an electric circuit configuration as shown in FIG. That is, 4 resistors
R ₁ to R ₄ constitute a bridge circuit, among which R ₁ ,
The resistors of semiconductor pressure-sensitive elements R _P1 and R _P2 are used as R ₂ , and the input voltage V _IN of the bridge circuit is a DC voltage stabilized by a constant voltage circuit 1 .

Therefore, in this bridge circuit, the resistances R ₁ and R ₂ of the semiconductor pressure sensitive elements R _P1 and R _P2 are as follows: R ₁ = R ₁₀ (1+α ₁ t) + ΔR ₁₀ (1 + β ₁ t) …(1) R ₂ = It is expressed as R ₂₀ (1+α ₂ t)−ΔR ₂₀ (1+β ₂ t) (2). However, R ₁₀ and R ₂₀ are the resistance values when the temperature is 0°C and the pressure is 0, ΔR ₁₀ and ΔR ₂₀ are the resistance values that change when pressure is applied at the temperature of 0°C, α ₁ ,
α ₂ , β ₁ , β ₂ are respective resistance temperature coefficients.

For ease of explanation, the coefficients of equations (1) and (2) are expressed as α ₁ =α ₂ =α, β ₁ =β ₂ =β, Δ
When R ₁₀ = ΔR ₂₀ = ΔR, the output voltage change (span) ΔVout for a certain pressure is ΔVout=V _IN ΔR・(1+βt)/(R ₁₀ +R ₂₀
)(1+αt)...(3) Among these, β usually has a negative temperature coefficient, but it can be made close to 0 depending on the manufacturing conditions of the pressure sensitive elements R _P1 and R _P2 . however,
Since α is a value determined by the material (Si) of the pressure sensitive elements R _P1 and R _P2 , when the temperature increases, Δ
Vout decreases.

Therefore, in order to compensate for the temperature of the span in a pressure transmitter, a configuration as shown in FIG. 2 has conventionally been adopted. That is, in this pressure transmitter, a thermistor 2 having a negative temperature coefficient of resistance is inserted between the bridge circuit and the positive polarity side of the constant voltage circuit 1.
The input voltage V _IN applied to the bridge circuit is changed in response to temperature changes to compensate.

However, in this span compensation method, the thermistor 2
The temperature of the resistance characteristics of the pressure sensitive elements R _P1 and R _P2
It is extremely difficult to match the resistance characteristics.
For this reason, even if span temperature compensation is possible, the compensation range is limited to a very narrow range.

In addition, as another example of the span temperature compensation method,
It is possible to drive the bridge circuit with a constant current, but in this case, the adjustment of the zero point and span and the nonlinearity compensation circuit of the pressure sensitive elements R _P1 and R _P2 become complicated, so it is not a good method. .

The present invention has been made in view of the above-mentioned circumstances, and has a temperature coefficient of resistance equal to or larger than the temperature coefficient of resistance of a pressure-sensitive element forming a bridge circuit on the input side of an operational amplifier forming a constant voltage circuit. A pressure transmitter is provided in which a resistive element through which a constant current flows is connected, thereby achieving good span temperature compensation over a wide temperature change range.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. The bridge circuit 11 shown in FIG. 3 is composed of resistances R _{1 and R 2 of pressure sensing elements R P1 and R P2 and ordinary fixed resistances R 3 and R 4 as in} the conventional case, and the bridge circuit 11 is supplied with power. A constant voltage circuit 14 that supplies input voltage V _IN is connected between terminals 12 and 13.

This constant voltage circuit 14 includes a power supply circuit 15 as a DC voltage generation source for obtaining the input voltage V _IN of the bridge circuit 11, a constant current source 16 connected between the output terminals of the circuit 15, and a sensor. Pressure element R _P
1 , a span temperature compensation circuit consisting of a resistance element 17 having a resistance temperature coefficient equal to or larger than the resistance temperature coefficient of R _P2 , and a resistance element 1 in the same circuit.
An operational amplifier 20 differentially amplifies the voltage V _REF across the terminal 7 and the divided voltage obtained by the voltage dividing resistors 18 and 19 inserted between the power supply terminals of the bridge circuit 11. It is composed of a semiconductor control element 21 that controls the voltage V _IN .

In the pressure transmitter having the above configuration, the input voltage V _IN of the bridge circuit 11 and the voltage V _REF across the resistance element 17 supplied to the positive input terminal of the operational amplifier 20 can be expressed by the following equation.

V _IN = R ₅ + R ₆ / R ₆ V _REF ...(4) Therefore, when calculating the output voltage change (span) ΔVout for a certain pressure from equations (3) and (4), ΔVout = ΔR/(R ₁₀ +R ₂₀ )・R ₅ +R ₆ /R
₆・1+βt/1+αtV _REF … (5) R ₅ and R ₆ are the resistance values of the voltage dividing resistors 18 and 19.

Therefore, as is clear from equation (5), if V _REF has a temperature coefficient of 1+αt/1+βt, it is possible to perform temperature compensation for the span. To this end, when the temperature changes, a constant current source 16 causes a constant current to flow through the resistance element 17, so that the temperature coefficient of the resistance element 17 becomes 1+αt/1+βt. That is, as shown in FIG. 3, a series circuit consisting of a constant current source 16 and a resistor element 17 is inserted between the output terminals of the power supply circuit 15, and their common part is connected to the positive input terminal of the operational amplifier 20. By applying a voltage across the element 17, temperature compensation of the span becomes possible. Moreover, for the resistance temperature coefficient of the resistance element 17, for example, when β=0, the resistance temperature coefficient is the same as that of the pressure sensitive elements R _P1 and R _P2 , and when β<0, the resistance temperature coefficient of the pressure sensitive element R _P
1 , a material with a higher temperature coefficient of resistance than R _P2 may be used.

Generally, the semiconductor pressure-sensitive elements R _P1 and R _P2 use silicon single crystal as a material, and the temperature coefficient of resistance is about 2000 to 2500 ppm, so the resistance element 1
If a material with relatively linear temperature-resistance characteristics such as Ni or Cu is used for 7, good span temperature compensation can be performed over a wide temperature change range even when β<0.

Next, FIG. 4 shows another example of the pressure transmitter of the present invention, in which a variable resistor 22 is connected in parallel to a span temperature-compensating resistance element 17. With such a configuration, the temperature compensation value of the span can be arbitrarily changed by varying the variable resistor 22 connected in parallel to the resistance element 17. The variable resistor 22 may have a small resistance temperature coefficient.

It goes without saying that the pressure transmitter shown in FIGS. 3 and 4 can also be applied to a pressure transmitter that transmits the differential pressure between two pressures.

As described in detail above, according to the present invention, the resistance temperature coefficient of the pressure sensitive element constituting the bridge circuit is connected to the input side of the voltage control operational amplifier constituting the constant voltage circuit that supplies the input voltage to the bridge circuit. By connecting a resistor element that receives a constant current with the same or larger resistance temperature coefficient and controlling the voltage using the voltage obtained across this resistor element, a good span can be achieved over a wide temperature change range. Temperature compensation can be performed. Further, it is sufficient to add a constant current source and a relatively easily manufactured resistance element to a conventional constant voltage circuit using an operational amplifier, and therefore, it can be realized with a simple circuit configuration.

[Brief explanation of the drawing]

1 and 2 are circuit configuration diagrams of a conventional pressure transmitter, FIG. 3 is a circuit configuration diagram of a pressure transmitter according to the present invention, and FIG. 4 is a pressure transmission diagram illustrating another embodiment of the present invention. FIG. 3 is a circuit configuration diagram of the device. 11... Bridge circuit, R _P1 , R _P2 ... Pressure sensitive element,
_R1 to _R4 ...Resistor, 14...Constant voltage circuit, 15...Power supply circuit, 16...Constant current source, 17...Resistance element, 18,
19... Voltage dividing resistor, 20... Operational amplifier, 22... Variable resistor.

Claims (1)

[Scope of Claims] 1. A pressure transmitter that configures a bridge circuit using a resistor of a semiconductor pressure-sensitive element and converts pressure into an electrical signal and transmits the same, comprising: a constant voltage circuit that supplies an input voltage to the bridge circuit. The output terminal of a voltage dividing resistor circuit inserted between the input voltage supply terminals of the bridge circuit is connected to one input side of the operational amplifier for voltage control, and the constant current source and resistor element output a predetermined constant current to the other input side. are connected in series, and a predetermined constant current is applied from the constant current source to the resistive element, so that the resistive element has the same resistance temperature coefficient as the semiconductor pressure sensitive element. or a larger resistance temperature coefficient, and the output of the operational amplifier is obtained as the input voltage of the bridge circuit through a semiconductor control element, thereby performing span temperature compensation. pressure transmitter.