JP2748196B2 - Correction method of temperature dependence of chemical sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention generally relates to a humidity sensor, an oxygen sensor, a hydrogen sensor, a hydrocarbon sensor, a carbon monoxide sensor, a nitrogen oxide sensor, and other chemical mediated intercalation functions. The present invention relates to a method for correcting temperature dependency of a sensor, and more particularly to a method for correcting temperature dependency of a chemical sensor whose temperature dependency is non-linear.

[0002]

2. Description of the Related Art For example, the amount of a specific component in an object such as a gaseous phase or a liquid phase (specifically, the amount of moisture in the air, the sealing gas in a closed vessel such as a transformer filled with insulating oil, etc.) Various types of measuring devices for measuring the amount of water in water or insulating oil, the amount of water in seal gas or oil in various oil tanks, etc.) have semiconductors whose impedance changes according to changes in the amount of the specific component. A type sensor, an electrolyte type sensor, a capacitance type sensor or the like is used. As is well known, such a sensor has a temperature dependency in the capturing ability of the sensor, so that the measured quantity needs to be corrected with the temperature. Normally, this correction is
As shown in FIG. 1, the temperature dependence is good linearity.

That is, in order to correct the temperature dependence of this type of sensor, for example, in detecting the amount of moisture, a circuit configuration in which a temperature detecting circuit is incorporated in a moisture amount detecting circuit is adopted as shown in FIG. ing. Here, to supply an AC voltage of constant frequency to the humidity sensor R _H of the detection and the detection circuit 2 via a DC blocking capacitor from the oscillator circuit 1, amplifies the detection output in response to the impedance change of the humidity sensor R _H The signal is amplified by the circuit 3 and the amplified output is supplied to the arithmetic circuit 4 as a voltage output representing the amount of water. Meanwhile, for correcting the temperature dependency of the humidity sensor R _H, and connect the temperature sensor R _T which resistance changes according to a change in temperature to the temperature detection and amplification circuit 5, corresponding to the resistance change of the temperature sensor R _T The detected voltage output is detected and amplified, and the amplified output is supplied to the arithmetic circuit 4 as a temperature correction voltage output. Which adds the two voltage output which is supplied the arithmetic circuit 4 (or in some cases the subtraction) to the voltage signal obtained by correcting the temperature dependency of the humidity sensor R _H, and outputs it as a voltage signal representative of the true moisture content It is.

[0004]

As described above, since the correction amount conventionally corresponds to the measured temperature value T, if the value determined by the circuit constant is α, the temperature correction amount Δ becomes Δ = α · T. Become.

However, the temperature dependence of a chemical sensor is not limited to a good linearity, and a chemical sensor having a non-linear temperature dependence may be used depending on the application. For example, as shown in FIG. 5, when the temperature coefficient of the temperature-dependent characteristic of the sensor changes (non-linearity) and the temperature coefficient differs depending on the measured amount, a large error occurs in the conventional temperature correction method. There was a serious drawback that it could not be put to practical use.

Further, to correct the temperature dependence of the non-linearity, a considerably complicated circuit configuration is required, and a correction circuit must be configured so that various temperature coefficients can be set. For this reason, the number of parts is greatly increased, the power consumption is increased, the size is increased, and the cost is considerably increased.

Accordingly, an object of the present invention is to provide a method for correcting the temperature dependence of a chemical sensor which can accurately correct the temperature dependence of non-linearity by arithmetic processing without taking a complicated circuit configuration. It is to provide.

[0008]

The above object is achieved by a method for correcting temperature dependence of a chemical sensor according to the present invention. In summary, the present invention relates to a measuring apparatus including a measured quantity detection circuit for detecting a measured quantity to be measured using a chemical sensor and a temperature detection circuit for detecting a temperature at the time of measurement. The measured quantity supplied from the measured quantity detection circuit to the arithmetic unit without temperature correction is denoted by DP ', the value representing the temperature supplied from the temperature detection circuit to the arithmetic unit is denoted by T, and the temperature-corrected measured quantity is measured. When the true value of the quantity is DP, the following equation DP = DP '+ (A * DP' + B) * (TC) ² (where A, B and C are constants) is set in the arithmetic unit. Calculating the true value DP of the temperature-corrected measured quantity by an arithmetic process in the arithmetic device based on the arithmetic expression, and correcting the temperature dependency of the chemical sensor. This is a method for correcting dependence.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Figure 1 is a circuit diagram showing an example of a moisture content detecting apparatus according to the present invention method, a semiconductor-type humidity sensor R _H in which the impedance changes according to the change in water content is used as a chemical sensor. This moisture content detection circuit includes two serially connected inverters 11 and 12 such as a C-MOS type Schmidt inverter;
A humidity sensor R _H , which is a pulse frequency determining element inserted into a feedback circuit of the preceding inverter 11, a switch SW ₁ composed of a three-state buffer connected in series with the humidity sensor R _H , A CR oscillation circuit that generates a square wave pulse signal related to the amount of water is constituted by a fixed-capacitance capacitor C that is a pulse frequency determining element connected between the input and the ground, and a humidity sensor R _H that is a pulse frequency determining element. The impedance of the oscillating circuit changes in accordance with the change in the amount of water, so that the output frequency of the CR oscillating circuit is changed correspondingly. The output frequency of the oscillation circuit is detected by counting the input digital signal, and To calculate the amount of water to respond.

Further, the humidity sensor R _H for correcting the temperature dependency of, for example, the temperature sensor R _T and a switch S consisting of 3-state buffers of the resistance change type, such as a thermistor
And inserted into the feedback circuit of the W ₂ of the series circuit of the same previous stage inverter 11 constitute a CR oscillation circuit for generating a square-wave pulse signal relating to the temperature, the resistance of the temperature sensor R _T is the pulse frequency determining element is the temperature The output frequency of the CR oscillation circuit is correspondingly changed by changing the output of the CR oscillation circuit, and this oscillation output, that is, a square wave pulse signal is sent to the microcomputer 13, and the temperature corresponding to the frequency is changed in the same manner as in the case of the water content. Is calculated. Each switch S
A control signal is supplied to W ₁ and SW ₂ from the microcomputer 13 via control lines 14 and 15, respectively, and these switches are turned on and off. That is, the switch SW ₁ is turned on by a control signal from the microcomputer 13, the switch SW ₂ is turned off, it constitutes the normal water content detection circuit, contrast, switch SW ₁ through the control signal from the microcomputer 13 There turned off, the switch SW ₂ is turned on, constitutes a normal temperature detection circuit. These detection circuits are switched and controlled by a control signal from the microcomputer 13 to supply the moisture content output from the moisture content detection circuit and the temperature output from the temperature detection circuit to the microcomputer 13 alternately, for example. The arithmetic processing based on a predetermined arithmetic expression in the above section corrects the water content output value according to the temperature output value, thereby preventing an error due to a temperature change. Thus, since the water content detection circuit and the temperature detection circuit can be configured with one simple circuit configuration, the number of components increases as in the case where the temperature detection circuit is provided separately,
The disadvantages such as an increase in power consumption, an increase in the size of the device, and an increase in cost are eliminated.

[0011] Figure 2 is a characteristic diagram showing an example of the temperature dependency of the humidity sensor R _H, which is used in the moisture content detecting device,
Take the impedance of the humidity sensor R _H on the vertical axis, in which took the dew point on the horizontal axis. Thus the temperature dependence of the humidity sensor R _H is exhibited nonlinear, and the measured quantity, if the dew point, the temperature coefficient depending differs in this example, the conventional as described above taken a complicated circuit configuration I had no choice.

In this embodiment, an output value (output value not subjected to temperature correction) representing the dew point from the moisture amount detection circuit is DP ', and a temperature from the temperature detection circuit is DP in the moisture amount detection device having the above-described structure. When the output value to be represented is T, the true dew point of which the temperature has been corrected, that is, the true value DP of the dew point is calculated by the following equation set in the microcomputer 13.

DP = DP '+ (A * DP' + B) * (T
-C) ² where A, B and C are constants determined by the characteristics of the sensor.

Now, assuming that the reference characteristic of the temperature dependency of the humidity sensor R _H is a curve F at a temperature T = 25 ° C. in FIG. 2, the temperature around the humidity sensor R _H at the time of measuring the dew point is 2
When the temperature is 5 ° C., when an output value DP ′ representing a dew point not subjected to temperature correction from the moisture detection circuit is input to the microcomputer 13, the dew point based on the reference characteristic curve F of FIG. 2 is calculated as DP ′. Here, in the above equation, DP = DP ', and the second term on the right-hand side which is a temperature-dependent correction term [(A * DP' + B) * (TC) ² ]
Becomes 0 (because the constant C = 25), the dew point DP 'based on the reference characteristic curve F calculated by the microcomputer 13 based on the output value indicating the dew point from the moisture content detection circuit is a true dew point. And the true value DP of the dew point can be easily obtained. On the other hand, the humidity sensor R
_If the temperature at the time of measuring the dew point around _H is 45 ° C., for example, the true value DP of the dew point is based on the characteristic curve G at the temperature of 45 ° C. the output values not is inputted, the dew point D based on the reference characteristic curve F of the humidity sensor R _H
P 'is calculated. Next, the microcomputer 13 performs an arithmetic process based on the above-mentioned arithmetic expression based on the output value DP 'representing the dew point which has not been temperature-corrected and the temperature value T representing the temperature of 45 ° C. inputted from the temperature detecting circuit, and the humidity sensor R A true value DP of the dew point in which the temperature dependency of _H is sufficiently corrected is calculated. That is, as is clear from FIG.
The true value DP of the dew point at 5 ° C. is DP = DP ′ + ΔDP, where ΔDP corresponds to the temperature-dependent correction term (the second term on the right side) of the above equation, and ΔDP = (A * DP ′ + B) *
(TC) ² .

Note that the constants A, B, and C in the above arithmetic expressions are determined by the characteristics of the sensor, and are obtained by measuring in advance at a predetermined measured amount and temperature.

Thus, by performing the arithmetic processing in the microcomputer 13 using the above arithmetic expression, the temperature dependence of the humidity sensor _RH can be reduced without having to take a complicated circuit configuration even when the temperature at the time of measurement varies. , The true value DP of the dew point can be easily calculated.

The above embodiment is merely an example of the present invention, and it goes without saying that the present invention can be easily applied to various devices using a chemical sensor other than a humidity sensor. Further, the circuit configuration, elements used, and the like shown in the above embodiments can be arbitrarily changed as necessary. For example, a capacitance sensor using an aluminum oxide film or the like may be used as the humidity sensor. In the case of the capacitance sensor, the other pulse frequency determining element of the oscillation circuit is a resistor (impedance element). Of course. Further, an electronic switch or a logic gate other than the three-state buffer may be used, or an analog switch may be used. Of course, an inverter other than the C-MOS Schmitt inverter and other circuit elements can be used, and an element other than a resistance change type temperature sensor (temperature detection element) or a microcomputer may be used. Further, the oscillating means may generate a pulse other than a square wave pulse.

[0018]

As described above, according to the present invention,
Since the temperature dependence of the chemical sensor is corrected by performing an arithmetic process based on an arithmetic expression set in the arithmetic unit, even if the temperature dependence of the chemical sensor is non-linear, Even when the temperature coefficient differs depending on the measured amount, the temperature dependency of the chemical sensor can be sufficiently corrected. Therefore, even if any temperature-dependent chemical sensor is used, a measurement error due to a temperature change is very small, and there is a remarkable effect that highly accurate measurement can be performed. In addition, since the temperature detection function can be added by adding only a minimum number of elements, the size of the device can be increased without increasing the number of components and power consumption compared to the case where a temperature detection circuit is provided separately. There is also an effect that the temperature change can be accurately detected without any disadvantages such as the disadvantage of increasing the cost and increasing the cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a water content detection device to which the method of the present invention is applied.

FIG. 2 is a characteristic curve diagram showing temperature dependence of a humidity sensor used in the moisture content detection device of FIG.

FIG. 3 is a characteristic curve showing the temperature dependence of a humidity sensor used in a conventional moisture content detection device.

FIG. 4 is a circuit connection diagram showing an example of a conventional moisture detection device incorporating a temperature detection circuit for correcting the temperature dependency of the humidity sensor of FIG.

FIG. 5 is a characteristic curve diagram illustrating an example of temperature dependence of non-linearity of a humidity sensor.

[Explanation of symbols]

11, 12 C-MOS Schmidt inverter 13 microcomputer 15 control lines R _H humidity sensor R _T temperature sensor SW _1, SW ₂ 3-state buffer C condenser

Claims (2)

(57) [Claims] 1. A measuring apparatus comprising: a measured quantity detection circuit for detecting a measured quantity to be measured using a chemical sensor; and a temperature detection circuit for detecting a temperature at the time of measurement. It is assumed that the measured quantity supplied from the circuit to the arithmetic unit without temperature correction is DP ', the value representing the temperature supplied from the temperature detection circuit to the arithmetic unit is T, and the true value of the temperature-corrected measured quantity is represented by T'. When the value is DP, the following equation is set in the arithmetic unit: DP = DP '+ (A * DP' + B) * (TC) ² (A, B and C are constants) Calculating the corrected true value DP of the measured quantity by an arithmetic processing based on the arithmetic expression in the arithmetic device, and correcting the temperature dependence of the chemical sensor. Correction method. 2. The method according to claim 1, wherein the measuring device selects, instead of the humidity sensor, an oscillating means including a humidity sensor as a pulse frequency determining element, and a temperature sensor for detecting a temperature in a subject where the humidity sensor is positioned. Means to be a pulse determining element of the oscillating means, and counting the number of pulses in a fixed time of the pulse signal output from the oscillating means,
2. The method according to claim 1, wherein the apparatus is a water content detecting device including digital processing means for calculating a water content or a temperature based on the counting result.