JPH0690168B2 - Humidity sensor device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a humidity sensor device.

[Technical background of the invention and its problems] Generally, for humidity measurement, as shown in FIG. 18, zinc oxide, chromium oxide, etc. are main components, and substances such as lithium-vanadium glass are added as moisture-sensitive components. Use a ceramic temperature sensor in which a lead wire (23) is attached to a porous electrode (22) formed on both sides of a porous ceramic sintered body (21) obtained by pressure molding and high-temperature sintering of powder. There are many.

However, the humidity sensor has an electrical resistance between the electrodes exponentially changes with respect to the relative humidity as shown in FIG. 19 due to the adsorption and desorption phenomenon of water molecules on the surface of the microcrystals of the sintered body. You can know the value of relative humidity by
Moreover, it has excellent features such as a simple structure, high stability, and no need for cleaning, but in order to convert the change in humidity into a change in electric signal, an alternating current can be applied to the humidity sensor as shown in Fig. 20. A constant voltage is applied to detect the resistance change of the humidity sensor as a change in voltage, or a constant AC voltage is applied to the humidity sensor as shown in Fig. 21 to change the resistance of the humidity sensor to a change in current. , Or the electric resistance of the humidity sensor changes exponentially with respect to the change in humidity, so an electric signal that is as proportional as possible to the humidity is taken out by passing through a logarithmic amplifier as shown in Fig. 22. The method was taken.

However, as shown in FIG. 19, the ceramic humidity sensor has a characteristic that the relative humidity and the logarithm of the electrical resistance of the sensor are approximately proportional, so the electrical resistance of the sensor can be measured by the measurement circuit shown in FIG. 20 or 21. There is a problem that relative humidity and output electric quantities thereof are not in a proportional relationship when simply converted into a change in voltage or current, and there is a large error even when measuring over a wide humidity range, making it extremely difficult to use. Also, in the measurement circuit shown in FIG. 22, the change in the electric resistance of the humidity sensor is passed through a logarithmic amplifier, so that the output signal has a close proportional relationship with the relative humidity, but the change in the electric resistance with respect to the humidity of the sensor does not change. As shown in Fig. 19, the logarithm of the resistance is not in perfect proportion to the relative humidity,
Since it is curved, it is unavoidable that the measurement error suddenly increases as the humidity measurement range widens.

Fig. 23 shows the humidity-voltage characteristics in this case.

Furthermore, the resistance value indicated by the ceramic humidity sensor is from several KΩ to M
Since it covers a wide range of Ω region, especially in the high resistance region on the low humidity side, the signal source impedance to the humidity-voltage or current conversion circuit becomes very high, so the noise resistance characteristic from the outside deteriorates and measurement error or This is a cause of erroneous operation, and there is a problem such as destruction of circuit elements when it is excessive, which is a serious problem for a humidity measuring circuit that often uses the humidity sensor part and the humidity-voltage conversion circuit part separately.

[Object of the Invention] The present invention has been made in view of the above points, and provides a humidity sensor device of high industrial value that can contribute to miniaturization that enables highly accurate and stable humidity measurement with a simple configuration. The purpose is to do.

SUMMARY OF THE INVENTION A humidity sensor device according to the present invention electrically connects a sensor electrode provided on both sides of a ceramic humidity sensor and a substrate electrode formed on an insulating substrate, and a synthetic resistance against humidity between the substrate electrodes. When the change characteristics of is linearly approximated for each of the three to four points, the square value of the correlation coefficient with respect to the approximate straight line is 0.98.
It is characterized in that a linearization resistor constituted by a thick film resistor in the range of 0 to 1.000 is connected in parallel, and further a characteristic correction resistor constituted by a thick film resistor is connected in series and / or in parallel to the substrate electrode. It is what

Embodiments of the Invention The details of the present invention will be described below based on embodiments with reference to the drawings.

Example Two variables, that is, the humidity and the change characteristic of the resistance value with respect to each humidity, linear approximation is performed at 3 to 4 points of the humidity, and the square value of the correlation coefficient obtained at that time, that is, the value obtained by the following formula Ask for.

Where r is the correlation coefficient, x Is the humidity value at each approximation point, y
Is the electric resistance value at each approximation point, and n is the number of approximation points.
You

It is known statistically that the square value of this correlation coefficient is 0 without correlation and becomes 1 when it completely matches the approximate straight line and always takes a value between 0 and 1.

Therefore, the degree of linearization can be known from the square value of the correlation coefficient. FIG. 1 shows a circuit diagram of a humidity sensor device according to an embodiment of the present invention in which a linearized resistor (2) is connected in parallel to a ceramic humidity sensor (1) and a characteristic correction resistor (3) is further connected in series. In the humidity sensor device, substrate electrodes (5), (6) and (7) made of, for example, gold, platinum or silver-palladium are formed on an insulating substrate (4) made of alumina as shown in FIG. Electrodes (5) (7)
A linearization resistor (2) made up of a thick film resistor is provided between them, and a characteristic correction resistor (3) made up of a thick film resistor is provided between the substrate electrodes (6) and (7).
And the sensor electrodes (8) provided on both sides of the substrate electrodes (5) and (6) and the ceramic humidity sensor (1).
Each of them is connected by a connecting line (9).

In the humidity sensor device thus configured, a characteristic correction resistor (3) having a resistance value of 28 KΩ is used, and linear approximation is performed for each humidity of 50% RH, 80% RH, 90% RH. FIG. 3 shows the squared value of the correlation coefficient obtained with respect to the value of the linearization resistance. In this way, when the linearization resistor (2) and the characteristic correction resistor (3) are connected to the ceramic humidity sensor (1), there is a linearization resistance value in which the change in electric resistance with respect to the change in humidity is the closest to a straight line. By the way, the resistance value is 80 KΩ as is clear from Fig. 3, and the square value of the correlation coefficient at that time is 1.0
It is 00, and if the square value of the correlation coefficient is less than 0.980, the linear function is poor, and highly accurate measurement is difficult and impractical.

As a result of examining the relationship between humidity and output voltage when a 30 KΩ linearized resistor having a squared correlation value of 0.975 was connected to the humidity sensor, the results are shown in FIG. Therefore, since the square value of the correlation is preferably in the range of 0.980 to 1.000, the linearization resistor (2) has a variation characteristic of the combined resistance of 3
It is assumed that the thick film resistance is such that the square value of the correlation coefficient with respect to the approximated straight line is in the range of 0.980 to 1.000 when the linear approximation is performed for each of the four humidity points.

Then, as shown in FIG. 5, the humidity sensor device shown in FIG. 2 was connected to the humidity-voltage conversion circuit (10) and the humidity-voltage characteristics were measured. As a result, as shown in FIG. Compared with the measurement values shown in FIG. 23 by the conventional measurement circuit shown in FIGS. 20 to 22 using the humidity sensor shown in the figure, a significant improvement in measurement accuracy is seen, and in this case, the humidity-electricity according to the present invention The relationship of resistance was as shown in FIG. 7, and the curve was corrected.

In the humidity sensor device configured as described above, the linearization resistor (2) and the characteristic correction resistor (3) are appropriately formed between the substrate electrodes (5) (6) (7) formed on the insulating substrate (4). Since it is composed of a thick film resistor, it is possible to reduce the size by reducing the size and man-hours compared with the case of using a normal discrete resistor, and to match the characteristics of the ceramic humidity sensor (1). Since the resistance value can be finely adjusted by the sandblast method or trimming by laser irradiation, it is possible to linearize it according to the sensor characteristics, which greatly contributes to the improvement of the characteristics.

In addition, when linearly approximating the change characteristic of the composite electric resistance with respect to humidity as a linearized resistance (2) from the thick film resistance for each of 3 to 4 points of humidity, the square value of the correlation coefficient for the approximate straight line is 0.980 to 1.000. Since we are using a range,
Regardless of the humidity measurement range, the change in resistance value with respect to humidity can be corrected to a proportional relationship, and simple and highly accurate humidity measurement without measurement error becomes possible.

In the above embodiment, the humidity sensor device configuration has been described by exemplifying the one shown in FIG. 2, but as shown in FIGS. 8 and 9, the substrate electrode is provided, for example, below the insulating substrate (4) made of alumina. (5) (6) (7) is formed and a linearized resistor (2) consisting of a thick film resistor is formed between the substrate electrodes (5) and (7).
A characteristic correction resistor (3) made of a thick film resistor is formed between the substrate electrodes (6) and (7), and the substrate electrodes (5), (6) and (7) of the insulating substrate (4) are provided above the substrate. A ceramic humidity sensor (1) is attached via an adhesive (11), and a space (1) for air circulation is provided between the sensor (1) and the insulating substrate (4).
2) is provided, and the sensor electrodes (8) constituting both surfaces of the humidity sensor (1) and the electrodes (5) and (6) are electrically connected by a connecting wire (9), or FIG. Substrate electrodes on an insulating substrate (13) made of an insulating coating formed by coating resin or glass on one side of the ceramic humidity sensor (1) having sensor electrodes (8) formed on both sides as shown in FIG. (5) (7) is formed, and the insulating substrate (1
A substrate electrode (6) is formed via 3) and the sensor electrode (8), and the electrodes (5) and (7) on the insulating substrate (13) are formed.
A linearization resistor (2) made up of a thick film resistor is provided between them, and a characteristic correction resistor (3) made up of a thick film resistor is provided between the substrate electrodes (6) and (7).
Forming the substrate electrode (5) and the humidity sensor (1)
It is also possible to use a structure in which the sensor electrode (8) formed on the other surface of is connected by the connecting wire (7). Also, the ninth
In the figure, the air circulation gap (12) is described as an example in which the insulating substrate (4) and the sensor electrode (8) are provided with a space therebetween via the adhesive (11), but the invention is not limited to this. Needless to say, for example, a structure in which a through hole is provided in an insulating substrate on which the sensor electrode is located may be used.

Further, in the above-described embodiment, the characteristic correction resistor is connected to the humidity sensor in series, but it may be connected in parallel or in combination of series and parallel. Furthermore, the signal source impedance seen from the humidity-voltage conversion circuit in the present embodiment on the sensor side is 100 K at most because the resistance value determined by the present invention is the maximum impedance.
Ω was a little over, and no unstable operation, malfunction, or increase in error due to high signal source impedance was observed at all, and an excellent effect was obtained.

Reference Example Next, a reference example of the present invention will be described. In the drawings, the same reference numerals as those of the embodiment are given to the same part names as those of the embodiment. That is, FIG. 11 is a circuit diagram of a humidity sensor device according to a reference example in which a linearization resistor (2) is connected in parallel to a ceramic humidity sensor (1) without using a characteristic correction resistor. As shown in FIG. 12, a linearized resistor (2) consisting of a thick film resistor is formed by printing between the substrate electrodes (5) and (6) provided on the insulating substrate (4), and the substrate electrodes (5) ( 6) and the sensor electrodes (8) provided on both sides of the ceramic humidity sensor (1) are connected by a connecting wire (9). Using the humidity sensor device configured in this way, 50% RH, A linear approximation was performed for each humidity of 80% RH and 90% RH, and the squared value of the correlation coefficient obtained at that time was expressed with respect to the value of the linearized resistance. There is a linearized resistance that changes the electrical resistance to the nearest straight line. The resistance value of is 110 KΩ as is clear from Fig. 13, and the squared value of the correlation coefficient at that time is 0.999, and if the squared value of the correlation coefficient is less than 0.980, the linear function is poor and high-precision measurement is difficult. Is not practical.

Therefore, from the above reference example, the square value of the correlation function is 0.980 to 1.000.
As the linearized resistance (2) has a good range, the linearized resistance (2) has a squared value of the correlation coefficient with respect to the approximated straight line when the change characteristic of the combined resistance is linearly approximated for each of 3 to 4 points of humidity.
It shall be composed of thick film resistors in the range of 0.980 to 1.000.

Then, as shown in FIG. 14, the humidity sensor device according to the present invention shown in FIG. 12 is connected to the humidity-voltage conversion circuit (8a) and the humidity-voltage characteristics are measured. As a result, as shown in FIG. In comparison with the measured values shown in FIG. 23 by the conventional measuring circuit shown in FIGS. 20 to 22 using the humidity sensor shown in FIG.

In the above reference example, the humidity sensor device configuration has been described by exemplifying the one shown in FIG. 12, but as shown in FIG. 16 and FIG. 17, similar to FIG. 8 to FIG. 10 described in the above embodiment. Alternatively, the structure of the insulating substrate (4) made of alumina may be changed. The same reference numerals are given to the partial names in FIGS. 16 and 17, and the description is omitted.

[Advantages of the Invention] According to the present invention, it is possible to correct the change in resistance value with respect to humidity into a proportional relationship and contribute to miniaturization, and
It is possible to obtain a humidity sensor device that is low in price, enables highly accurate humidity measurement, has low signal source impedance, and is stable and has high industrial value.

[Brief description of drawings]

1 is a circuit diagram of a humidity sensor device according to an embodiment of the present invention, FIG. 2 is a plan view of the humidity sensor device shown in FIG. 1, and FIG. 3 is a linearization in the humidity sensor device shown in FIG. FIG. 4 is a characteristic diagram showing the relationship between the resistance and the square value of the correlation coefficient, FIG. 4 is a relative humidity-output voltage characteristic diagram, and FIG. 5 is a circuit showing an example of a humidity measuring circuit using the humidity sensor device shown in FIG. Figure, 6th
The figure shows the humidity measured by the humidity measurement circuit shown in FIG.
FIG. 7 is a voltage characteristic diagram, FIG. 7 is a humidity-electric resistance characteristic diagram measured by FIG. 5, and FIGS. 8 and 9 are other examples of the humidity sensor device which is the humidity sensor circuit shown in FIG. FIG. 8 is a plan view, FIG. 9 is a side view, FIG. 10 is a plan view according to another embodiment of the humidity sensor device which is the humidity sensor circuit shown in FIG. 1, and FIG. 11 is a humidity according to a reference example. Circuit diagram of the sensor device, FIG. 12 is a plan view of the humidity sensor device shown in FIG.
FIG. 13 is a characteristic diagram showing the relationship between the linearized resistance and the squared value of the correlation coefficient in the humidity sensor device shown in FIG. 12, and FIG.
A circuit diagram showing an example of a humidity measuring circuit using the humidity sensor device shown in FIG. 15, FIG. 15 is a humidity-voltage characteristic diagram measured by the humidity measuring circuit shown in FIG. 14, and FIGS.
FIG. 18 is a plan view according to each of other reference examples of the humidity sensor device which is the humidity sensor circuit shown in FIG. 18, FIG. 18 is a sectional view showing a general structure of the ceramic humidity sensor, and FIG. 19 is a ceramic humidity sensor shown in FIG. 20 is a circuit diagram showing respective humidity measuring circuits according to a conventional example, and FIG. 23 is a relative humidity-output voltage characteristic diagram. (1) …… Ceramic humidity sensor, (2) …… Linearizing resistor (3) …… Characteristic correction resistor, (4) …… Insulating substrate (5) (6) (7) …… Board electrode, (8) …… Sensor electrode (9) …… Connecting wire, (11) …… Adhesive (12) …… Void

Claims (1)

[Claims] 1. A ceramic humidity sensor is provided with sensor electrodes provided on both sides thereof and a substrate electrode formed on an insulating substrate, which are electrically connected to each other. When linearly approximated for each humidity, the squared value of the correlation coefficient with respect to the approximated straight line is connected in parallel with a linearized resistor composed of a thick film resistor in the range of 0.980 to 1.000, and further in series and / or in parallel with the substrate electrode A humidity sensor device characterized in that a characteristic correction resistor constituted by a thick film resistor is connected thereto.