JPH11241962A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor capable of precisely measuring pressure without using a separately mounted heater. SOLUTION: This pressure sensor is provided with a resistive bridge circuit B comprising a pressure sensitive resistor 1, a voltage measuring circuit 7, a current control means 11 for performing the control of switching a measuring constant current value and a heating constant current value to the resistive bridge circuit B, a temperature sensor 12 for measuring the outside air temperature and a control parameter setting part 13 for setting the magnitude and/or current applying time of the heating constant current value. The heating current is carried to the resistance of the resistive bridge circuit B before and after the measurement of the pressure sensitive resistor 1 to regulate the temperature by the bridge resistor itself.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor for use in a gas chromatograph sample inlet.

[0002]

2. Description of the Related Art In a gas chromatograph, when a sample is introduced from a sample introduction section to a column, a sample is introduced while maintaining a constant column inlet pressure. I have.

FIG. 1 shows a configuration diagram of a pressure sensor conventionally used in a sample introduction device of a gas chromatograph. In the figure, 1 is a pressure-sensitive resistor by a strain gauge, 2
4 is a bridge resistance in the sensor, 5 is a constant current circuit, 6
Is an amplifier circuit, 7 is a voltage measurement circuit, and 8 and 9 are voltage measurement points.

A constant current circuit 5 supplies a constant current for measurement (generally several mA) to a bridge composed of 1 to 4. The voltage between the voltage measurement points 8 and 9 in the bridge composed of 1 to 4 is amplified by the amplifier circuit 6 and then measured by the voltage measurement circuit 7. When the pressure-sensitive resistor 1 is not exposed to the pressure to be measured, the pressure-sensitive resistor 1 and the bridge resistors 2 to 4 are selected to have substantially equal electric resistance values. Therefore, since the voltage difference between the voltage measurement points 8 and 9 is almost 0, the voltage measured by the voltage measurement circuit 7 is also close to 0.

When the pressure-sensitive resistor 1 is exposed to a measured pressure, the pressure-sensitive resistor 1 is distorted by the pressure. The pressure-sensitive resistor 1 has a characteristic that an electric resistance value changes when it is distorted. Thus, when the pressure-sensitive resistor 1 is exposed to pressure, the pressure-sensitive resistor 1
Is changed, a voltage difference is generated between the voltage measurement points 8 and 9, and the voltage difference is input to the amplifier circuit 6. as a result,
The voltage according to the observed pressure can be measured by the voltage measurement circuit 7.

[0006]

In the pressure sensor as described above, the resistance value of the heat-sensitive resistor or the bridge resistor changes according to the change of the outside air temperature. The measurement was difficult. for that reason,
Conventionally, when performing accurate measurement, a temperature control mechanism including a temperature sensor and a heater circuit for keeping the temperature of the bridge portion constant at, for example, 40 degrees Celsius was provided as a countermeasure against temperature, and the temperature was controlled so as to be constant. . However, for this reason, a heater for controlling the temperature had to be separately provided, which increased the number of parts and hindered miniaturization.

Accordingly, an object of the present invention is to provide a pressure sensor capable of performing stable pressure measurement without providing such a separate temperature control mechanism.

[0008]

A pressure sensor according to the present invention, which has been made to solve the above problems, has a resistance bridge circuit including a pressure-sensitive resistor whose resistance value changes with a change in pressure, and the resistance bridge circuit. A voltage measuring circuit for detecting the resistance value of the pressure-sensitive low antibody as a voltage value, a first constant current value flowing through the resistance bridge circuit when measuring the voltage value, and a second constant current value flowing when heating the resistance bridge circuit. Current control means for performing control for switching between the constant current value and a temperature sensor for measuring the outside air temperature, and the magnitude of the second constant current value and / or the second constant current value according to the temperature measured by the temperature sensor. Parameter setting means for setting the time for flowing the constant current value in the current control means.

In this pressure sensor, the resistance value of the pressure-sensitive resistor in the bridge resistor is changed to a voltage value by flowing a first constant current value (a small current that causes no or negligible heating by the resistor). Is measured as in the prior art, but the current control means switches the current to a second constant current value (a current that can heat the resistor), thereby heating the resistor with current, that is, using the resistor itself as a heater. By using this, heating is performed without attaching a separate heater, and the temperature is kept constant.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. FIG. 2 is a configuration diagram of a pressure sensor according to one embodiment of the present invention. 1 is a pressure-sensitive resistor, and 2 to 4 are bridge resistors in the sensor. Reference numeral 11 denotes a current control unit capable of generating a duty ratio and a current specified by a parameter setting unit described later, 6 denotes an amplifier circuit, 7 denotes a voltage measurement circuit, 8 and 9 denote voltage measurement points, and 12 measures outside air temperature. Temperature sensor.

Reference numeral 13 denotes a parameter setting unit, which has a built-in memory. The memory has an optimum current value flowing through the bridge when the bridge temperature is to be maintained at, for example, 40 degrees Celsius for each outside air temperature value. And the duty ratio are stored. Therefore, the optimum current value and the duty ratio according to the measurement value output from the temperature sensor 12 are determined by the parameter setting unit 13, and the parameter values are set in the current control unit 11.

The constant current control section 11 has a constant duty for measurement (generally several mA) with a preset duty ratio in the bridge B composed of 1 to 4 and a constant current for measurement determined by the parameter setting section 13. A heating constant current of several times the current is passed. This is shown in FIG.

In FIG. 3, T1 is a period of a current applied by the current control unit 11, T2 is a time for flowing a constant current for measurement, T3 is a time for flowing a constant current for heating, I1 is a current for measurement, I2 is a heating current. The current control unit 11 determines T based on the outside air temperature measured by the temperature sensor 12.
Each value of 1, T2, T3, and I1 is stored in a table as a table. The temperature of the entire bridge is I1
Is almost the same even if the current I2 flows, but I1 and I2 are set so as to rise when the current I2 flows. Further, the above table is created so that the temperature of the entire bridge is about 40 ° C. regardless of the outside air temperature.

The voltage between the voltage measuring points 8 and 9 in the bridge constituted by 1 to 4 is amplified by the amplifier circuit 6 and then measured by the voltage measuring circuit 7. When the pressure-sensitive resistor 1 is not exposed to the pressure to be measured, the pressure-sensitive resistor 1 and the bridge resistors 2 to 4 have substantially equal electric resistance values. Therefore, since the voltage difference between the voltage measurement points 8 and 9 is almost 0, the voltage measured by the voltage measurement circuit 7 is also close to 0.

When the pressure-sensitive resistor 1 is exposed to a measured pressure, the pressure-sensitive resistor 1 is distorted by the pressure. The pressure-sensitive resistor 1 has a characteristic that an electric resistance value changes when it is distorted. Therefore, the pressure-sensitive resistor 1
Is exposed to pressure, the resistance of the pressure-sensitive resistor 1 changes,
A voltage difference occurs between the voltage measurement units 8 and 9, and the voltage difference is input to the amplifier circuit 6. The current control unit 11 notifies the voltage measurement circuit 7 of the timing at which the current I1 flows. The voltage measurement circuit 7 measures a voltage difference between the voltage measurement points 8 and 9 while the current control unit 11 is flowing I1. As a result, the voltage according to the pressure to be observed can be measured by the voltage measurement circuit 7.

As described above, since the temperature of the bridge composed of 1 to 4 is maintained at about 40 ° C., an accurate pressure which is not affected by the outside air temperature can be measured.

In the above embodiment, both the setting of the heating current value and the time for supplying the heating current are changed, but the same effect can be obtained by changing only one of them.

Hereinafter, embodiments will be summarized. (1) A resistance bridge circuit including a pressure-sensitive resistor whose resistance value changes according to a pressure change, a voltage measurement circuit for detecting the resistance value of the pressure-sensitive low antibody in the resistance bridge circuit as a voltage value, A current control unit that has two current values and is capable of changing a duty ratio of the current values, and further includes a temperature sensor that can measure an outside air temperature; A pressure sensor, comprising: a current control unit that causes a current to flow through a resistor of the resistance bridge circuit at a duty ratio according to an output from the sensor.

[0019]

As described above, in the pressure sensor according to the present invention, the temperature is controlled by using the pressure sensor itself without providing a separate temperature control mechanism. In addition, accurate pressure can be measured without being affected by the outside temperature with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a conventional pressure sensor.

FIG. 2 is a configuration diagram of a pressure sensor according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a current controlled by a current control unit according to one embodiment of the present invention.

[Explanation of symbols]

 1: pressure-sensitive resistor 2 to 4: bridge resistor 5: constant current circuit 6: amplifier circuit 7: voltage measurement circuit 8, 9: voltage measurement point 11: current control unit 12: temperature sensor 13: parameter setting unit T1: cycle T2: Time for flowing constant current for measurement T3: Time for flowing constant current for heating I1: Current for measurement I2: Current for heating

Claims (1)

[Claims] 1. A resistance bridge circuit including a pressure-sensitive resistor whose resistance value changes according to a pressure change, a voltage measurement circuit for detecting a resistance value of a pressure-sensitive low antibody in the resistance bridge circuit as a voltage value, A first constant current value flowing through the resistance bridge circuit at the time of measuring the voltage value, a current control means for performing control to switch between a second constant current value flowing when heating the resistance bridge circuit, and measuring the outside air temperature A temperature sensor, and parameter setting means for setting the magnitude of the second constant current value or / and the time for flowing the second constant current value to the current control means in accordance with the temperature measured by the temperature sensor. Pressure sensor characterized by the above-mentioned.