JP2010127923A - Method for temperature correction in sensor for discovering the concentration of co2 gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct the temperature of an infrared sensor that is used as a sensor for discovering the concentration of CO<SB>2</SB>gas, and to prevent saturation of an amplifier that amplifies a signal from the infrared sensor and fluctuations in direct-current output voltage of the amplifier, thereby correcting the direct-current output voltage of the amplifier to be zero. <P>SOLUTION: The infrared sensor is placed in a space, and a bead-like temperature-detecting element that is used for detecting the temperature in the space is placed in the space so as to detect the temperature in an area around the infrared sensor. A temperature-detecting element having a negative temperature characteristic is inserted into a feedback circuit of an amplifier that amplifies a signal from the infrared sensor, and the negative temperature characteristic of the infrared sensor is corrected by rendering the amplification degree of temperature characteristic a positive temperature characteristic. As for the direct-current output voltage of an infrared sensor having a temperature characteristic, the direct-current output voltage is always corrected to be zero in the absence of a signal by adding an automatic zero correction circuit to an amplifier that amplifies a signal from the infrared sensor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a temperature correction method in a CO2 gas concentration value sensor.

As a conventional temperature correction method for a CO2 gas concentration value sensor, there is a method in which a heater and a temperature detection element are arranged in an adiabatic space and the temperature in this space is controlled to be constant. (For example, refer to Patent Document 1.)
JP 2000-213986 A

  Infrared sensors used for CO2 gas concentration value sensors generally have (−) temperature characteristics that the voltage sensitivity decreases as the temperature increases, and (+) temperature characteristics that the DC output voltage increases as the temperature increases. It is necessary to correct the temperature of the CO2 gas concentration sensor.

  The temperature of the infrared sensor changes due to a change in ambient temperature and light irradiation from a lamp that has passed through the detection gas.

  In addition, since the amplifier that amplifies the signal from the infrared sensor has a high amplification degree, it is saturated by the DC output voltage of the infrared sensor. If this DC output voltage has temperature characteristics, it cannot be handled by a normal zero correction circuit, and an auto zero correction circuit is required.

  In the conventional technique, a chip-shaped temperature detecting element is mounted on a printed circuit board, and the temperature in the chip is detected to control the temperature in the heat insulating space in which the infrared sensor is arranged to be constant.

  However, since the chip-shaped temperature detection element is mounted on the printed board, the temperature detected by the temperature detection element is not the temperature in the space but the temperature of the printed board.

  Therefore, the temperature in the space where the infrared sensor is disposed cannot be controlled to be constant, and the temperature of the printed circuit board in the vicinity of the infrared sensor is controlled.

  In addition, it is difficult to achieve control without fluctuation by such temperature control, and a large circuit is required to achieve control without fluctuation.

  As the temperature detection element for detecting the temperature in the space where the infrared sensor is arranged, a bead-shaped element is used and arranged in the space so as to detect the temperature in the vicinity of the infrared sensor.

  Rather than controlling the temperature in the space constant by the temperature detected by this temperature detection element, a temperature detection element having a temperature characteristic of (−) is provided in the feedback circuit of the amplifier that amplifies the signal from the infrared sensor. Insert the (+) characteristic into the temperature characteristic of the amplification degree to correct the (−) temperature characteristic of the voltage sensitivity of the infrared sensor.

  For DC output voltage with temperature characteristics, an auto-zero correction circuit is added to the amplifier that amplifies the signal from the infrared sensor, and the DC voltage when no signal appears is always controlled to zero.

  Rather than performing difficult temperature control, a temperature detection element with a temperature characteristic of (-) is inserted into the feedback circuit of the amplifier, so that the temperature characteristic of the amplification degree has a characteristic of (+) and is easy Corrects the temperature characteristics of the voltage sensitivity of the infrared sensor (-)

  In addition, the auto-zero correction circuit can cope with fluctuations in the DC output voltage of the infrared sensor.

  Hereinafter, an embodiment of the present invention will be described with reference to the thermistor arrangement diagram of FIG. 1, the signal amplification circuit from the infrared sensor of FIG. 2, and FIG.

  In order to detect the temperature in the space where the infrared sensor is disposed, a thermistor is disposed in the heat insulation space near the infrared sensor as shown in FIG.

  The thermistor is soldered to a thermistor soldering pad on the printed circuit board and arranged perpendicular to the board.

  Here, the light from the lamp that has passed through the detection gas is irradiated from above in FIG.

  With such a thermistor arrangement, the temperature in the vicinity of the infrared sensor can be detected.

  As shown in FIG. 2, the thermistor is connected in series with R_s and in parallel with R_p, and is inserted into the feedback circuit of the amplifier.

When the combined resistance value of the thermistor resistance values RTH, R_s and R_p is Rt,
Rt = (RTH + R_s) × R_p / ((RTH + R_s) + R_p) (1)
The amplification degree A of the amplifier is
A = R2 / R1 × (1 + R3 / Rt) --------------- (2)
It is expressed.

  In the equation (1), R_s adjusts the change in Rt due to the temperature gradient of the thermistor resistance value, and R_p functions to adjust the resistance value of Rt and set the amplification degree A. If R_s is small, the change with respect to the temperature of the amplifier becomes large, and if R_s is large, the change with respect to the temperature of the amplifier becomes small.

  Since the resistance value of the thermistor decreases as the temperature rises, the amplification factor A in equation (2) has a characteristic that increases as the temperature rises, and the infrared sensor characteristic that the voltage sensitivity decreases as the temperature rises can be corrected. it can.

  R_s is adjusted so that the temperature characteristic of the amplification degree corrects the temperature characteristic of the infrared sensor. These characteristics are shown in FIG.

  Next, the auto zero correction circuit will be described with reference to FIG.

  In FIG. 2, since the signal output of the infrared sensor is small, the amplification degree A is as large as 100 to 1000 times. On the other hand, the DC output voltage of the infrared sensor is generally around (+) 1 V, and the output of the amplifier is saturated by this voltage.

  Therefore, the DC output voltage of the amplifier is integrated by an integrator and applied to the input of the amplifier through R_bal.

  The output of the integrator is applied to the amplifier input with a voltage division ratio of R_bal and R_sig, and the signal from the infrared sensor is applied to the input of the amplifier with a voltage division ratio of R_sig and R_bal.

  Due to the (+) DC output voltage of the amplifier, the (-) voltage is output to the output of the integrator, which is the opposite of the (+) DC output voltage of the infrared sensor, and the (+) DC of the amplifier Reduce output voltage.

  Even with a slight (+) DC output voltage of the amplifier, a (−) voltage is output to the integrator output, and finally the DC output voltage of the amplifier becomes zero.

  Since the lamp is lit with a pulse width of about 1 second and flashes repeatedly for about 10 seconds, the signal from the infrared sensor is in the form of a pulse having a time constant of about 1 second.

  The time constant of the integrator is C × R4, and this value is set to about 200 seconds larger than 1 second. Therefore, the signal from the infrared sensor is averaged, and the DC output voltage of the integrator by this signal is averaged. There is no change.

  Therefore, the output change of the amplifier due to the fluctuation of the direct current output voltage due to the temperature change of the infrared sensor is always corrected, and the direct current output voltage of the amplifier becomes zero.

  Here, in order to correct the bias current of the operational amplifier used in the integrator, R4 = R5 is set.

  Thermistor layout   Signal amplification circuit from infrared sensor   Temperature characteristics of voltage sensitivity of infrared sensor and normalized amplification of amplifier

Explanation of symbols

FIG.
1 Thermistor 2 Infrared Sensor 3 Printed Circuit Board 4 Thermistor Lead Wire 5 Thermistor Soldering Pad
1 Lamp 2 Infrared sensor 3 Amplifier 4 Integrator 5 Thermistor 6 FET

Claims (2)

  In an infrared gas concentration sensor that uses a lamp that illuminates in a short time as a light source, a bead-shaped temperature detection element with a temperature characteristic of (-) is used in the space near the infrared sensor to detect the temperature of the infrared sensor. The temperature detection element is inserted into a feedback circuit of an amplifier that amplifies the signal from the infrared sensor, and the temperature characteristic of the amplification degree has a (+) temperature characteristic, and the temperature characteristic of the infrared sensor (−) Infrared type gas concentration value sensor comprising a temperature correction circuit for correcting the temperature.   In an infrared gas concentration sensor that uses a lamp that illuminates in a short time as a light source, the output voltage of the amplifier of the signal from the infrared sensor is integrated by an integrator having a time constant larger than the time constant of the signal. In addition to the input of the amplifier, the amplifier is prevented from saturation and fluctuation of the DC output voltage due to the DC output voltage having temperature characteristics from the infrared sensor, and the DC output voltage of the amplifier is corrected to zero. Infrared gas concentration sensor, equipped with an auto-zero correction circuit.

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