JPH0776762B2 - Electronic hygrometer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an electronic hygrometer, and in particular, for example, a digital electronic hygrometer equipped with a humidity detecting element whose capacitance value varies according to a change in humidity in the atmosphere. Regarding

TECHNICAL BACKGROUND OF THE INVENTION AND ITS PROBLEMS As is well known, in this type of digital electronic hygrometer, the capacitance value of the humidity sensitive element is changed according to the humidity change in the atmosphere, and the electric output is changed. The obtained product is used, and the analog voltage signal output from the humidity-sensitive element is amplified by an amplifier according to the change in the capacitance value of the element, and then the analog / digital converter (hereinafter referred to as "A / D converter"). The digital electronic circuit control device (hereinafter simply referred to as "microcomputer") such as a mylocomputer, a microprocessor, etc. is detected by the humidity sensitive element based on the digital signal. It is designed to calculate the humidity value in the atmosphere.

By the way, as is apparent from the above description, the conventional digital electronic hygrometer is based on the analog voltage signal output from the humidity sensitive element whose capacitance value is variable according to the humidity change in the atmosphere described above. In order for the microcomputer to calculate the humidity value in the atmosphere, an amplifier for amplifying an analog signal output from the humidity sensitive element between the humidity sensitive element and the microcomputer and an analog signal output from the amplifier are used. Since it was necessary to connect an A / D converter that converts to a digital signal, the entire circuit including the amplifier such as a microcomputer, A / D converter, etc.
Since it could not be made into a chip LSI, there was a limit to achieving miniaturization and low power consumption, and it was difficult to reduce the cost.

Therefore, in view of the above-mentioned fact, as a result of the present inventors' repeated research, the digital electronic hygrometer as described above does not use a relatively expensive A / D converter, but the function of the A / D converter is different. It has been found that the number of components of the circuit can be reduced by complementing the technical means of (1) and the entire circuit can be integrated into one chip LSI.

The present invention is based on such a new finding.

Therefore, the present invention has been made in view of the above-mentioned background, and its purpose is to eliminate a relatively expensive A / D converter and reduce the number of circuit components. Therefore, it is possible to reduce the size of the entire circuit to a single chip LSI, reduce power consumption, and reduce costs, and eliminate the effects of variations in component constants in the circuit and temperature characteristics. It is to provide an electronic hygrometer with accuracy.

Means for Solving the Problems The above object is achieved by the electronic hygrometer according to the present invention. In summary, the present invention relates to a square-wave pulse signal generator, a humidity-sensing element connected to the square-wave pulse signal generator and having a capacitance value that varies according to a change in humidity in the atmosphere, and the square-wave pulse signal. A square wave pulse according to the variable capacitance value of the humidity sensing element, the resistance sensing element being connected to a generator and forming a CR time constant circuit with the capacitance value of the humidity sensing element. Oscillating means for outputting a signal, counting the frequency of the square wave pulse signal output from the oscillating means,
An electronic hygrometer having a digital arithmetic processing means for obtaining a humidity value in the atmosphere based on the counting result, wherein a reference capacitance element is connected in parallel to the humidity detection element,
First switching means for opening / closing the humidity detecting element side and second switching means for opening / closing the reference capacitance element side are provided, and by the digital arithmetic processing means,
A square wave output from the oscillating means when only the first switching means is closed, which corresponds to the ratio of the capacitance value of the humidity sensing element to the capacitance value of the reference capacitance element. A ratio between the oscillation frequency of the pulse signal and the oscillation frequency of the square wave pulse signal output from the oscillation means when only the second switching means is closed is calculated,
The electronic hygrometer is characterized in that a humidity value in the atmosphere is obtained based on the calculation result.

Examples Hereinafter, examples according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram for explaining the principle of the electronic hygrometer of the present invention. An outline of the electronic hygrometer of the present invention is, as is apparent with reference to FIG. 1, an oscillating means, that is, a square wave pulse oscillator 1,
It comprises a digital arithmetic processing means or a microcomputer 9 for receiving the output signal of the square wave pulse oscillator 1. The square wave pulse oscillator 1 described above includes a square wave pulse signal generator, that is, an inverter element 7 that outputs a square wave pulse signal that is a logic level signal, and the inverter element 7
The resistance element 3 connected to the feedback circuit and the humidity detecting element 5 forming a CR time constant circuit, that is, a CR oscillation circuit, between the resistance element 3 and the electric resistance value of the resistance element 3. As the humidity detecting element 5, a humidity sensitive element of which the electrostatic capacitance value is variable according to a change in humidity in the atmosphere, that is, a so-called electrostatic capacitance variable type is used. Examples of the variable capacitance type humidity sensitive element described above include tantalum, titanium, niobium,
A dielectric anodic oxide film is formed by anodic oxidation on an anodic substrate made of a valve metal such as aluminum or hafnium, and the whole or a part of the dielectric anodic oxide film is coated with, for example, manganese nitrate. A semiconducting metal oxide layer such as manganese dioxide was formed by the thermal decomposition of such a pyrolytic metal salt, and a water vapor vortex conductive electrode was formed on it by using carbon and silver paint. There is a structure like this. The process of humidity detection by the variable capacitance type humidity sensitive element having the above-described structure is as follows. That is, when the humidity detecting element 5 adsorbs moisture in the air according to the relative humidity, this moisture acts as a counter electrode of the dielectric anodized film, and in the case of high humidity, this electrode area increases. Therefore, a high capacitance is obtained, and when the humidity is low, the low capacitance is detected as a signal, and finally the change in relative humidity in the air is detected as a change in capacitance. As described above, the variable capacitance type humidity detecting element has high measurement accuracy and sensitivity over 0 to 100% RH as shown in FIG. 2, and as shown in FIG. ,
The response of adsorption and dehumidification is also very excellent.

The inverter element 7 is formed between the capacitance value of the humidity detecting element 5 and the resistance element 3 by changing the capacitance value of the humidity detecting element 5 according to a change in humidity in the atmosphere. When the oscillation frequency of the CR oscillation circuit is changed, a square wave pulse signal having a frequency corresponding to the oscillation frequency is output. For example, a C-MOS short inverter is used for the inverter element 7, and by using the C-MOS short inverter for the inverter element 7 in this way, cost reduction and power consumption reduction are achieved. For example, a stable square wave pulse signal can be obtained even at a frequency on the order of 100 KHz.

The above-mentioned micro computer 9 has a CPU for performing arithmetic and logical operations, a counter for counting the square wave pulse signal output from the square wave pulse oscillator 1, a memory for storing necessary data, an input memory, and the like. Equipped with output ports and so on. Examples of the data stored in the memory of the microcomputer 9 include humidity-capacitance value characteristic data of the humidity detecting element 5 as shown in FIG. 2 and temperature compensation value of the humidity detecting element 5. Data, an expression representing the relationship between the oscillation frequency f of the square wave pulse signal output from the square wave pulse oscillator 1 shown in FIG. 1 and the capacitance value C of the humidity detecting element 5. However, VO: output voltage of the square wave pulse oscillator 1 VTH: Hi level threshold voltage of the inverter element 7 (that is, C-MOS shift inverter) VTL: the inverter element 7 (that is, C-MOS shift inverter) LO level threshold voltage of k: There is a constant. The CPU of the microcomputer 9 counts the frequency f of the square wave pulse signal output from the square wave pulse oscillator 1 described above, and the oscillation frequency f of the counted square wave pulse signal and the expression stored in the memory. And the capacitance value C of the humidity detecting element 5 is calculated from
From the calculated electrostatic capacitance value C of the humidity detecting element 5 and the humidity-electrostatic capacitance value characteristic data of the humidity detecting element 5 shown in FIG. Will be asked.

As described above, according to the present invention, the cost and the power consumption can be reduced by using the C-MOS synchronous inverter as the inverter element 7, and at the same time, for example, on the order of 100 KHz. A square wave pulse signal that is stable with respect to frequency can be obtained. Further, the humidity detecting element 5 is connected to the input side of the inverter element 7, and is connected to the capacitance value of the humidity detecting element 5 and the feedback circuit of the inverter element 7 according to the humidity change of the humidity detecting element 5. The square wave pulse signal having a frequency corresponding to the variable oscillation frequency in the CR oscillation circuit formed between the resistance element 3 and the resistor element 3 is output from the inverter element 7 and the square wave pulse signal is counted by the microcomputer 9. By doing so, it was possible to obtain the humidity value in the atmosphere, which made it possible to form a single chip LSI for the entire circuit.

FIG. 4 shows an electronic hygrometer according to the first embodiment of the present invention. The outline of the electronic hygrometer according to the first embodiment of the present invention is as follows.
As is apparent from FIG. 4, the reference capacitance element CO11 is connected in parallel to the humidity detecting element 5 connected to the input side of the inverter element 7 of the square wave oscillator 1 shown in FIG. The first switching means or SW1 for opening / closing the side connected to the humidity detecting element 5 and the second switching means or SW2 for opening / closing the side connected to the reference capacitance element CO11. Is provided, and only the SW1 corresponding to the ratio CO / C of the capacitance value C of the humidity detecting element 5 and the capacitance value CO of the reference capacitance element CO11 is closed by the microcomputer. The oscillation frequency fH of the square-wave pulse signal output from the square-wave pulse oscillator 1 and the oscillation frequency fO of the square-wave pulse signal output from the square-wave pulse oscillator 1 when only the SW2 is closed. And the ratio rf≡fH / fO is calculated and rf≡fH By calculating the value of C at C = CO / rf from the relational expression of / fO = CO / C,
The humidity value in the atmosphere is determined from the value of C and the data shown in FIG. The reason why the square wave pulse oscillator 1 is configured as described above is as follows. That is, as a result of the experiments performed by the inventors of the present invention using the square wave pulse oscillator 1 shown in FIG. 1, the oscillation frequency f of the oscillator 1 is determined by the resistance value R of the resistance element 3 and the inverter element 7. It was found that it is somewhat affected by the Hi level threshold voltage VTH, the LO level threshold voltage VTL of the same element 7, the output voltage VO of the oscillator 1 and the variation of the value of the constant k and the temperature characteristics. . Therefore, as described above, the present inventors connect the reference capacitance element CO11 to the humidity detection element 5 in parallel, and when the SW1 and SW2 are provided and one of them is closed, the other is opened. Oscillation frequency fH when only SW1 is closed Can be obtained by ), Oscillation frequency fO when only SW2 is closed Can be obtained by ) Is counted by the microcomputer 9 and then the ratio of fH to fO is taken to obtain the above VT.
By deleting H, VTL, VO, k, and R and determining the value of the oscillation frequency f only by the value of CO / C, more accurate humidity measurement value data could be obtained. In the reference capacitance element CO11 described above, the variation of the electrostatic capacitance value due to the influence of the temperature variation or the like is almost negligible as compared with the variation of the characteristic values of VTH, VTL, VO, R, k and the like. , VTH, VTL, V by determining the value of rf
By making the values of O, R, k, etc. to be canceled so that the value of rf is determined only by changing the capacitance value C of the humidity detecting element 5, more accurate humidity measurement can be performed. It was done like this. In addition, the above SW1, SW2,
A normal analog switch or a 3-state buffer is used.

FIG. 5 shows an electronic hygrometer according to a second embodiment of the invention. The outline of the electronic hygrometer according to the second embodiment of the present invention is as follows.
As is apparent from FIG. 5, in the square wave pulse oscillator 1 having the circuit configuration shown in FIG. 4, the humidity detecting element 5 connected to the input side of the inverter element 7 is connected to the humidity detecting element 5. A capacitance value C1 which is larger than the capacitance value C in the steady state of the humidity detection element 5 which forms a combined capacitance C'with the capacitance value C of the humidity detection element 5 is used. 1 protective capacitance element, that is, the capacitor C1 is connected in series, and the humidity detecting element 5 and the capacitor C1
And the combined capacitance C'formed by connecting in series. With respect to the combined capacity C ′, further combined capacity C ″
A second protective capacitance element, that is, a capacitor C2 having a capacitance value C2 smaller than the capacitance value C in the steady state of the humidity detecting element 5 forming (C ″ = C ′ + C2) is connected in parallel. However, regarding the upper limit value of the combined capacitance C ″ of the humidity detecting element 5, the capacitor C1 and the capacitor C2, the capacitance value C1 of the capacitor C1 and the capacitance value C2 of the capacitor C2.
It is regulated so that it is less than the sum value C1 + C2, and the combined capacitance C ″ of the humidity detecting element 5, the capacitor C1 and the capacitor C2.
The lower limit value of is regulated so as not to be less than the capacitance value C2 of the capacitor C2. The reason why the square wave pulse oscillator 1 is configured as described above is that the variable range of the electrostatic capacitance value C of the humidity detecting element 5 that varies according to the humidity change in the atmosphere is equal to or more than a predetermined value. Alternatively, the square wave pulse oscillator 1 to the micro computer 9 is controlled so that it does not fall below a certain value.
On the other hand, this is to prevent a square wave pulse signal having a frequency higher than the oscillation frequency data having a fixed range stored in the memory of the microcomputer 9 from being output. If a square wave pulse signal having a frequency outside the set range of the oscillation frequency is output from the square wave pulse oscillator 1,
The CPU outputs a command to display an overflow or underflow to a display unit (not shown). In the present embodiment, in order to regulate the variable range of the capacitance value C of the humidity detecting element 5 within a certain range, as described above, the capacitance value C of the humidity detecting element 5 in the steady state is lower than that in the steady state. A capacitor C1 having a large capacitance C1 is connected in series with the humidity detecting element 5, and a capacitor C2 having a capacitance value C2 smaller than the capacitance value C of the humidity detecting element 5 is connected to the humidity detecting element. 5 and capacitor
By utilizing the parallel connection with the series body with C1 to make the combined capacitance C'of the series body of the humidity detecting element 5 and the capacitor C1 not larger than the electrostatic capacitance C1 of the capacitor C1. The value of the combined capacitance C ″ formed by the humidity detecting element 5, the capacitor C1 and the capacitor C2 becomes C ″ <C ′ + C2 when the capacitance value C of the humidity detecting element 5 increases. On the other hand, when the electrostatic capacitance value C of the humidity detecting element 5 decreases and the C ′ becomes very small, the C ″ is restricted to C ″> C2. is there.

In the electronic hygrometer according to each of the embodiments of the present invention, the humidity detecting element 5 is connected to the input side of the inverter element 7, and the resistance element 3 is connected to the feedback circuit side of the inverter element 7. The humidity detecting element 5 may be connected to the feedback circuit side of the inverter element 7, and the resistance element 3 may be connected to the input side of the inverter element 7.

EFFECTS OF THE INVENTION As described above, according to the present invention, the reference capacitance element is connected in parallel to the humidity detection element, and the first switching means for opening / closing the humidity detection element side and the reference capacitance element side. And a second switching means for opening / closing, the digital arithmetic processing means corresponding to the ratio of the capacitance value of the humidity detecting element to the capacitance value of the reference capacitance element. Oscillation frequency of a square wave pulse signal output from the oscillating means when only the first switching means is closed and a square wave pulse output from the oscillating means when only the second switching means is closed. Since the ratio of the signal to the oscillating frequency is calculated and the humidity value in the atmosphere is calculated based on the calculation result, the relatively expensive A / D
Since a converter is not required and the number of circuit components can be reduced, it is possible to realize a single chip LSI for the entire circuit, which in turn makes it possible to achieve miniaturization, low power consumption, and low cost. In addition, it is possible to provide a highly accurate electronic hygrometer by eliminating the influence of variations in component constants in the circuit, temperature characteristics, and the like.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram for explaining the principle of the electronic hygrometer of the present invention. FIG. 2 is a humidity-capacitance value characteristic diagram of the humidity detecting element used in the electronic hygrometer shown in FIG. FIG. 3 is a characteristic diagram showing absorption / dehumidification response characteristics of the humidity detecting element used in the electronic hygrometer shown in FIG. FIG. 4 is a circuit configuration diagram of the electronic hygrometer according to the first embodiment of the present invention. FIG. 5 is a circuit configuration diagram of the electronic hygrometer according to the second embodiment of the present invention. 1: Square wave pulse signal oscillator 3: Resistor element 5: Humidity detection element 7: Inverter element 9: Microcomputer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 61-40553 (JP, A) JP-A 61-28854 (JP, A) JP-A 59-53265 (JP, A) JP-A 60- 238715 (JP, A)

Claims (5)

[Claims] 1. A square wave pulse signal generator, a humidity detecting element connected to the square wave pulse signal generator, the capacitance value of which changes in accordance with a change in humidity in the atmosphere, and the square wave pulse signal generator. And a resistance element that forms a CR time constant circuit between the capacitance value of the humidity sensing element and a square wave pulse signal according to the variable capacitance value of the humidity sensing element. An electronic hygrometer having an oscillating means for outputting and a frequency of a square wave pulse signal output from the oscillating means, and a digital arithmetic processing means for obtaining a humidity value in the atmosphere based on the counting result, A reference capacitance element is connected in parallel to the humidity detection element,
First switching means for opening / closing the humidity detecting element side and second switching means for opening / closing the reference capacitance element side are provided, and by the digital arithmetic processing means,
A square wave output from the oscillating means when only the first switching means is closed, which corresponds to the ratio of the capacitance value of the humidity sensing element to the capacitance value of the reference capacitance element. A ratio between the oscillation frequency of the pulse signal and the oscillation frequency of the square wave pulse signal output from the oscillation means when only the second switching means is closed is calculated,
An electronic hygrometer characterized in that a humidity value in the atmosphere is obtained based on the calculation result. 2. The humidity detecting element is connected to an input side of the square wave pulse signal generator, and the resistance element is connected to a feedback circuit of the square wave pulse signal generator. The electronic hygrometer according to claim 1, which is characterized. 3. The electronic hygrometer according to claim 1 or 2, wherein the square wave pulse signal generator is an inverter element. 4. The electronic hygrometer according to claim 3, wherein the inverter element is a C-MOS dummy inverter. 5. An electrostatic capacitance in a steady state of the humidity detecting element, which forms a combined capacitance with the capacitance of the humidity detecting element connected to the square wave pulse signal generator. A first protective capacitance element having a capacitance value larger than the capacitance value is connected in series, and a combined capacitance formed by the humidity detection element and the first protection capacitance element connected in series is formed. On the other hand, a second capacitance having a smaller capacitance value than the capacitance value in the steady state of the humidity detecting element that further forms a capacitance with the capacitance.
Are connected in parallel, and the upper limit value of the combined capacitance of all the elements is the sum of the electrostatic capacitance value of the first protective capacitance element and the electrostatic capacitance value of the second protective capacitance element. It is regulated so as to be less than a value, and the lower limit value of the combined capacitance of all the elements is regulated so as not to be less than or equal to the electrostatic capacitance value of the second protective capacitance element. The electronic hygrometer according to any one of items 1 to 4.