JPS6375546A - Electronic hydroscope - Google Patents

Abstract

PURPOSE:To miniaturize an instrument and to reduce power consumption, and a cost by counting the frequency of a rectangular pulse signal outputted by an oscillating means. CONSTITUTION:A rectangular wave pulse oscillator 1 consists of an inverter element 7, a resistance element 3, and a humidity detecting element 5. This element 7 outputs the rectangular pulse signal of frequency corresponding to the oscillation frequency of a CR oscillation circuit formed of the electrostatic capacity value of the element 5 and element 3 when the electrostatic capacity value of the element 5 varies with atmospheric humidity and the oscillation frequency of the CR oscillation circuit varies. Further, a microcomputer 9 is provided with a CPU, a counter which counts the rectangular wave pulse signal outputted by the oscillator 1, a memory for storing a control program, etc., and necessary data, etc. The CPU of the microcomputer 9 counts the frequency (f) of the rectangular wave pulse signal outputted by the oscillator 1 and computes the electrostatic capacity value C of the element 5, thereby finding the atmospheric humidity value from the capacity value C and humidity- electrostatic capacitance characteristic data of the element 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to an electronic hygrometer, and more particularly, to a digital electronic hygrometer equipped with a humidity sensing element whose capacitance value varies according to changes in atmospheric humidity. Regarding.

As is well known, this type of digital electronic hygrometer has a humidity sensing element whose capacitance value changes according to changes in atmospheric humidity, and produces an electrical output. After amplifying the analog voltage signal output from the humidity sensing element according to the variable capacitance value of the humidity sensing element using an amplifier, an analog/digital converter (hereinafter referred to as rA/D converter) is used. A digital electronic circuit control device such as a microcomputer or microprocessor (hereinafter simply referred to as a "microcomputer") converts the atmospheric air detected by the moisture sensing element into a digital signal based on the digital signal. The humidity value is calculated.

By the way, as is clear from the above, conventional digital electronic hygrometers are based on the analog voltage signal output from the humidity sensing element whose capacitance value changes according to the changes in atmospheric humidity. When the microcomputer calculates the humidity value in the atmosphere, an amplifier for amplifying the analog signal output from the humidity sensing element is provided between the humidity sensing element and the microcomputer, and an amplifier for amplifying the analog signal output from the amplifier. Since it was necessary to connect the A/D converter that converts the signal to a digital signal, it was not possible to integrate the entire circuit, including the microcomputer, amplifier, A/D converter, etc., into a single chip LSI. , hence miniaturization,
There is a natural limit to reducing power consumption, and it has also been difficult to reduce costs.

Therefore, in view of the above-mentioned facts, the inventors of the present invention and others have conducted repeated research and have found that, without using a relatively expensive A/D converter in a digital electronic hygrometer as described in 2. By complementing this with other technical means, the number of parts in the circuit can be reduced, and the entire circuit can be integrated into a one-chip LSI.
I discovered that it is possible to

The present invention is based on such novel findings.

SUMMARY OF THE INVENTION Therefore, the present invention was devised based on the circumstances described above, and its purpose is to reduce the number of components in a circuit by eliminating a relatively expensive A/D converter. It is an object of the present invention to provide an electronic hygrometer that can realize miniaturization, low power consumption, and low cost by integrating the entire circuit into a single-chip LSI.

. 1. The above objectives are achieved by the electronic hygrometer according to the present invention. To summarize, the present invention provides a square wave pulse signal generator, a humidity sensing element connected to the square wave pulse signal generator and whose capacitance value varies according to changes in atmospheric humidity, and the square wave pulse signal generator. a resistance element connected to the generator and forming a CR time constant circuit with the capacitance value of the humidity sensing element, the square wave pulse responsive to variation of the capacitance value of the humidity sensing element; oscillating means for outputting a signal; counting the frequency of a square wave pulse signal output from the oscillating means;
The electronic hygrometer is characterized by having a digital arithmetic processing means for determining a humidity value in the atmosphere based on the counting results.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Takai Maruki F. will explain embodiments according to the present invention with reference to the drawings.

FIG. 1 shows an electronic hygrometer according to a first embodiment of the invention. The outline of the electronic hygrometer according to the first embodiment of the present invention is as follows:
As is clear from FIG. 1, it consists of an oscillation stage f, ie, a square wave pulse oscillator 1, and a digital arithmetic processing means, ie, a microcomputer 9, which receives 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 which is a logic level signal, a resistor element 3 connected to a feedback circuit of the inverter element 7, and a resistor element 3 connected to a feedback circuit of the inverter element 7. The humidity sensing element 5 forms a CR constant circuit, that is, a CR oscillation circuit, with the electrical resistance value of the resistance element 3. The humidity sensing element 5 is a so-called variable capacitance type humidity sensing element whose capacitance value changes according to changes in atmospheric humidity. The above-mentioned variable capacitance type moisture sensing element is produced by forming a dielectric anodic oxide film by anodizing on an anode base made of a valve metal such as tantalum, titanium, niobium, aluminum, or hafnium. Furthermore, a semiconducting metal oxide layer such as manganese dioxide is formed on the entire surface or a part of the dielectric anodic oxide film by thermal decomposition of a thermally decomposable metal salt such as manganese nitrate. Some have a structure in which a water vapor permeable conductive electrode is formed on top using carbon and silver paint. 1- The process of humidity detection using the variable capacitance type humidity sensing element having the above structure is as follows.

That is, when the humidity sensing element 5 adsorbs moisture in the air according to the relative humidity, this moisture acts as a counter electrode of the dielectric anodic oxide film, and in the case of high humidity, the area of this electrode increases. Therefore, a high capacitance is obtained, and in the case of low humidity, a low capacitance is detected as a signal, and finally a change in relative humidity in the air is detected as a change in capacitance. The variable capacitance type humidity sensing element described above has high measurement accuracy and sensitivity over a range of 0 to 100% RH, as shown in FIG. The responsiveness of groove removal is also very good.

The inverter element 7 has a structure in which the capacitance value of the humidity sensing element 5 changes according to changes in atmospheric humidity, so that a capacitance value is formed between the capacitance value of the humidity sensing element 5 and the resistance element 3. When the oscillation frequency in the CR oscillation circuit is varied, a square wave pulse signal having a frequency corresponding to the oscillation frequency is output. In this example,
A C-MOS Schmidt inverter is used for the inverter element 7, and in this way, the inverter element 7 has a C-MOS Schmidt inverter.
- By using a MOS Schmitt inverter,
In addition to lowering costs and power consumption, e.g.
A stable square wave pulse signal can be obtained even at frequencies on the order of 0 KHz.

The microcomputer 9 described above includes a CPU that performs arithmetic operations and logical operations, a counter that counts the square wave pulse signal output from the square wave pulse oscillator 1, a control program, etc., and also has a memory that stores necessary data, and an input. It is equipped with output boats, etc. The microcomputer 9
The data stored in the memory includes, for example, the humidity-capacitance characteristic data of the humidity sensing element 5 as shown in FIG. 2, the temperature compensation value data of the humidity sensing element 5, the first Square wave pulse oscillator 1 illustrated in the figure
Expression expressing the relationship between the oscillation frequency f of the square wave pulse signal outputted from the humidity sensing element 5 and the capacitance value C of the humidity sensing element 5. However, vO: the output voltage of the square wave pulse oscillator 1 VTR: the inverter element 7 ( (ie, C-MOS Schmitt inverter) Hr level threshold voltage VTL: LO level threshold voltage k of the inverter element 7 (ie, C-MOS Schmitt inverter): 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, and calculates the oscillation frequency f of the counted square wave pulse signal and 0 stored in the memory. The capacitance value C of the humidity sensing element 5 is calculated from the formula, and the calculated capacitance value C of the humidity sensing element 5 and the humidity sensing value shown in FIG. 2 stored in the memory are calculated. The atmospheric humidity value is determined from the humidity-capacitance characteristic data of the element 5.

As explained above, according to the first embodiment of the present invention, a C-MOS Schmitt inverter is used for the inverter element 7, so that cost and power consumption can be reduced. At the same time, a stable square wave pulse signal can be obtained even at frequencies on the order of, for example, 100 KHz.

Further, the humidity sensing element 5 is connected to the input side of the inverter element 7, and the capacitance value of the humidity sensing element 5 is connected to the feedback circuit of the inverter element 7 according to the humidity change of the humidity sensing element 5. The CR formed between the resistor element 3
Since a square wave pulse signal of a frequency corresponding to the variation of the oscillation frequency in the oscillation circuit is output from the inverter element 7 and the square wave pulse signal is counted by the microcomputer 9, the humidity value in the atmosphere is determined.
It became possible to implement the entire circuit into a single-chip LSI.

FIG. 4 shows an electronic hygrometer according to a second embodiment of the invention. 1 of the electronic hygrometer according to the second embodiment of the present invention! In short, as is clear with reference to FIG. 4, the reference capacitive element Co is
11 are connected in parallel, and a first switching means, that is, SWI, opens/closes the side to which the humidity sensing element 5 is connected, and a second switching means opens/closes the side to which the reference capacitance element Co11 is connected. means, SW2, and the microcomputer detects only the SW1 corresponding to the ratio: CO/C between the capacitance value C of the humidity sensing element 5 and the capacitance value CO of the reference capacitance element Co11. The oscillation frequency fH of the square wave pulse signal output from the square wave pulse oscillator l when SW2 is closed, and the oscillation frequency fH of the square wave pulse signal output from the square wave pulse oscillator 1 when only the SW2 is closed. Ratio r f to oscillation frequency fO
= f H/ f O, calculate r f E f H/
From the relational expression of f 0 = CO/C, C = CO/ r f
By determining the -cct7) value, the humidity value in the atmosphere can be determined from the value of C and the data shown in FIG. 2. The reason why the square wave pulse oscillator 1 is configured as described above is as follows. That is, as a result of experiments conducted by the present inventors using the square wave pulse oscillator 1 shown in FIG. Level threshold voltage VTR2
It has been found that the LO level 1/threshold voltage VTL of the element 7, the output voltage 2o of the oscillator 1, variations in constant values, temperature characteristics, etc. have some influence.

Therefore, as described in -1-, the present inventors connected the reference capacitive element Co11 in parallel to the humidity sensing element 5, and
When WI and SW2 are provided and one is closed, the other is opened, and the oscillation frequency is determined by the oscillation frequency when only SWI is closed. ), oscillation frequency fO when only SW2 is closed (fo=1/rk-
The R-C computer 9 calculates the ratio of fH and fO and calculates the VTR, VTL, and VO.
, by eliminating R and determining the value of the oscillation frequency f only by the value of CO/C, it was possible to obtain more accurate humidity measurement value data. The reference capacitance element Co11 mentioned above has a capacitance value whose fluctuation due to the influence of temperature changes is so small that it can be ignored compared to the characteristic value fluctuations of the VTH, VTL, VO1R, etc. By calculating the value of rf, that is, the value of f h / f o , the values of VTH, VTL, VO, R, etc. described in in are canceled, and the value of rf becomes the value of capacitance C of the humidity sensing element 5. By making it determined only by variables,
This allows for more accurate humidity measurement. Note that a normal analog switch or a 3-state buffer is used for the above-mentioned SWI and SW2.

FIG. 5 shows an electronic hygrometer according to a third embodiment of the invention. The outline of the electronic hygrometer according to the third embodiment of the present invention is as follows:
As is clear with reference to FIG. 5, in the square wave pulse oscillator l having the circuit configuration shown in FIG. A capacitance value C1 larger than a capacitance value C in a steady state of the humidity sensing element 5 forming a composite capacitance C' between the capacitance value C of the humidity sensing element 5;
A first protective capacitance element, that is, a capacitor C1 having a capacitor C1 is connected in series, and the humidity sensing element 5 and the capacitor C1 are connected in series, and a combined capacitance C' is further connected between the humidity sensing element 5 and the capacitor C1. 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 sensing element 5, forming (C'' = C'+ C2), is connected in parallel. The upper limit of the combined capacitance C'' of the humidity sensing element 5, capacitor C1, and capacitor C2 must be less than the sum of the capacitance value CI of the capacitor C1 and the capacitance value C2 of the capacitor C2. The lower limit value of the combined capacitance C'' of the humidity sensing element 5, the capacitor C1, and the capacitor C2 is regulated so that it does not exceed 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 capacitance value C of the humidity sensing element 5, which varies according to changes in atmospheric humidity, is equal to or greater than a preset constant value. Alternatively, by regulating the frequency so that it does not fall below a certain value, the square wave pulse oscillator 1 can transmit to the microcomputer 9 a frequency higher than the oscillation frequency data having a certain range stored in the memory of the microcomputer 9. This is to prevent a square wave pulse signal from being output. In addition, if a square wave pulse signal with a frequency outside the setting range of the oscillation frequency is output from the square wave pulse oscillator 1, the CPU will notify the display section (not shown) of an overflow or underflow signal. It is designed to output a command to display the following. In this embodiment, in order to regulate the variable range of the capacitance value C of the humidity sensing element f-5 within a certain range, the capacitance value C of the humidity sensing element 5 in a steady state is set as described above. A capacitance C greater than
1 is connected in series with the humidity sensing element 5, and a capacitor C2 having a capacitance value c2 smaller than the capacitance value C of the humidity sensing element 5 is connected in series with the humidity sensing element 5. The humidity sensing element 5 and the capacitor C are connected in parallel to the series body with the capacitor C1.
Using the fact that the combined capacitance 1B-c' of the series body with 5. When the capacitance value C of the humidity sensing element 5 increases, the value of the composite capacitance c'' formed by the capacitor c1 and the capacitor C2 becomes C''<C'+
On the other hand, when the capacitance value C of the humidity sensing element 5 decreases and the C' becomes very small, the c'' is restricted to C''> 02. It is something.

In the electronic hygrometer according to each of the embodiments of the present invention, the humidity sensing 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 sensing element 5 may be connected to the feedback circuit side of the inverter element 7, and the resistor element T-3 may be connected to the input side of the inverter element f-7.

1. As explained above, according to the present invention, the frequency of the square wave pulse signal output from the oscillation means is counted, and the humidity value in the atmosphere is determined based on the counting result. This eliminates the need for a relatively expensive A/D converter and reduces the number of components in the circuit, making it possible to implement the entire circuit on a single chip LSI, resulting in smaller size and lower power consumption. , it is possible to provide an electronic hygrometer that can reduce costs.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an electronic hygrometer according to a first embodiment of the present invention. FIG. 2 is a humidity-capacitance characteristic diagram of the humidity sensing element f used in the electronic hygrometer shown in FIG. 1. FIG. 3 is a characteristic diagram showing the moisture absorption and desorption response characteristics of the humidity sensing element used in the electronic humidity IT shown in FIG. 1. FIG. 4 is a circuit diagram of an electronic humidity IT according to a second embodiment of the present invention. FIG. 5 is a circuit diagram of an electronic hygrometer according to a third embodiment of the present invention. ■ = Square wave pulse signal oscillator 3: Resistance element 5: Humidity detection element 7: Inverter element 9: Microcomputer

Claims (1)

[Scope of Claims] 1) A square wave pulse signal generator, a humidity sensing element connected to the square wave pulse signal generator and whose capacitance value varies according to changes in atmospheric humidity, and the square wave pulse signal generator. C between the capacitance value of the humidity sensing element connected to the signal generator.
oscillation means for outputting a square wave pulse signal according to variation of the capacitance value of the humidity sensing element; and a square wave pulse signal output from the oscillation means. 1. An electronic hygrometer, comprising: a digital calculation processing means for counting the frequency of the hygrometer and calculating a humidity value in the atmosphere based on the counting result. 2) The humidity sensing element is connected to the input side of the square wave pulse signal generator, and the resistance element is connected to the input side of the square wave pulse signal generator.
The electronic hygrometer according to claim 1, wherein the electronic hygrometer is connected to a feedback circuit of the square wave pulse signal generator. 3) The electronic hygrometer according to claim 1 or 2, wherein the square wave pulse signal generator is an inverter element. 4) An electronic hygrometer according to claim 3, wherein the inverter element is a C-MOS Schmitt inverter. 5) A humidity sensor connected to the input side of the square wave pulse signal generator. A reference capacitance element is connected in parallel to the element,
A first switching means for opening/closing the humidity sensing element side and a second switching means for opening/closing the reference capacitance element side are provided, and the digital arithmetic processing means
a square wave output from the oscillation means when only the first switching means corresponding to the ratio of the capacitance value of the humidity sensing element to the capacitance value of the reference capacitance element is closed; calculating the 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;
The electronic hygrometer according to any one of claims 1 to 4, wherein an atmospheric humidity value is determined based on the calculation result. 6) Static capacitance of the humidity sensing element in a steady state forming a composite capacitance with the humidity sensing element connected to the input side of the square wave pulse signal generator. A first protective capacitor element having a capacitance value larger than the capacitance value is connected in series, and a composite capacitor formed by connecting the humidity sensing element and the first protective capacitor element in series. On the other hand, a second element having a capacitance value smaller than the capacitance value in the steady state of the humidity sensing element forming a composite capacitance with the composite capacitance.
protective capacitance elements are connected in parallel, and the upper limit of the combined capacitance of all the elements is the sum of the capacitance value of the first protective capacitance element and the capacitance value of the second protective capacitance element. The lower limit value of the combined capacitance of all the elements is regulated so as not to be less than the capacitance value of the second protective capacitance element. The electronic hygrometer described in Section 5.