JPS5832152A - humidity detection device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity detection device and a high-precision humidity detection device using a solid state sensing element.

Conventionally, there are humidity sensing elements that utilize changes in electrical resistance due to physical adsorption of water onto the surface of a substance. This humidity sensing element has the advantage that it can be easily connected to an electronic circuit and has a wide range of applications because it can treat changes in humidity as changes in electrical resistance, and has been actively developed. However, the aforementioned sensing elements also have problems.

This is because the amount of physical adsorption of water changes not only with humidity but also with temperature, so it is necessary to correct the temperature when detecting humidity, and because the change in electrical resistance due to physical adsorption of water is exponential, the electrical resistance value It is impossible to obtain a linear output with respect to humidity without logarithmically converting it, and when performing humidity detection.

3.-0 When a DC voltage is applied to the humidity sensing element for a long period of time, electrolysis and polarization of water occur, which accelerates characteristic changes and deterioration of the humidity sensing element.

Generally, in devices that display humidity, etc.

4. It is preferable that the output of the humidity detection device be linear with respect to humidity. This is because if the humidity is nonlinear, it is necessary to perform logarithmic conversion using a nonlinear circuit such as a logarithmic amplifier. Furthermore, in order to prevent changes and deterioration of characteristics due to the application of a DC voltage, it is necessary to perform measurements using an AC voltage.

Note that, as the above-mentioned logarithmic converter, a nonlinear element such as a transistor or a diode is generally used as the logarithmic conversion element. According to this, although highly accurate logarithmic conversion can be performed, the electrical characteristics of the logarithmic conversion element are easily influenced by temperature, and it is necessary to maintain the logarithmic conversion element at a constant temperature or compensate for changes in electrical characteristics due to temperature. Therefore, it is necessary to thermally couple the logarithmic conversion element to the logarithmic conversion element using a resistor or the like that can handle the temperature dependence, and to perform temperature compensation using a circuit. Furthermore, the measurement method using alternating current voltage requires a rectifier circuit and an amplifier tube, which has drawbacks such as a tendency to reduce accuracy and a complicated circuit.

From the above, in addition to the humidity detection circuit, a temperature detection and compensation circuit is required, making the circuit complex.

The number of adjustment points increases, which significantly increases the manufacturing cost of the device.

The present invention is useful in overcoming all of the aforementioned problems.

That is, 5 the present invention uses a diode as a nonlinear element for logarithmic conversion of the resistance of the humidity sensing element, performs all logarithmic conversion while detecting the entire ambient temperature with this diode, and separates the logarithmic conversion output and the temperature detection signal by a circuit, The temperature detection signal is used to perform all temperature compensation in logarithmic conversion and temperature compensation for humidity detection output, and what conventional devices required two temperature detection circuits can now be done with one temperature detection. It can also serve as logarithmic conversion. In addition, the voltage applied to the humidity sensing element is a pulse, and by reducing its duty ratio, the average DC voltage is reduced.

This prevents element deterioration and characteristic changes. And 6.

By measuring the resistance of the humidity sensing element when the applied pulse voltage is at its peak value.

During AC measurement, F can also be measured with high accuracy and the 5 circuit can be simplified.

A more detailed explanation will be given below using one drawing.

FIG. 1 is a diagram showing the humidity dependence of the electrical resistance of the humidity sensing element used in the present invention. The temperature in the figure indicates the ambient temperature.

The humidity sensing element used here is made of MgCr.
A sintered body made of a porous metal oxide containing 20<i;
Its characteristics can be expressed by the following formula.

However, T: Ambient temperature (0K) TO22 humidity temperature (0K) H: Relative humidity (96) B: Temperature coefficient (0K) Mu: Humidity coefficient (1/%) R8: Element resistance (Ω) Ro: T =To, resistance when H==O(f%) (
2) Here, the ambient temperature T can be expressed by the following formula: T=To +Δt ・・・・・・・・・−・・・・・・・・・
・・・・・・・・・・・・・・・・・・(2) However, Δt
is the difference between the ambient temperature T- and the reference temperature Tυ. formula(
If we completely substitute equation (2) into 1) and transform it.

Rs BB In =- person) I-1-,. +Jt−π・・・・・・
......Side O The ambient temperature range for humidity detection is limited to 10 to 60°C, the reference temperature Toi is 30a°, that is, 36°C, and the difference Δ between the ambient temperature T and the reference temperature TO is ±26° in total. Then, equation 1 (3) can be transformed into the following equation.

Here, there is a relationship of To)Δt, and Equation 1 (4) can be approximated as follows.

Here, B and To are constants, and if B'-B/T02, Equation 1 (6) becomes No'. If Δ is 1 ± 2s (0K), the error due to setting is approximately 0.7% or less at maximum. Yes, there is no problem in practice.

The above are the characteristics of the humidity sensing element used in the present invention.

FIG. 2 is a block diagram of an embodiment of the humidity detection device of the present invention.

In the figure, 1 is a pulse controller, 2.3.4 is an operational amplifier, 6.6 is a voltage memory, and 7 is an arithmetic unit.

8 is a diode, 9 is a humidity sensing element (resistance value iRs), and 10 to 14 are resistors (respective resistance value j).

are Rlo, R11, R12, Rls, and R14).

FIG. 3 is a timing chart showing the operation of the humidity detection device, and shows waveforms at various parts in FIG.

This embodiment will be explained using FIGS. 2 and 3.

The pulse controller 1 outputs signals S+, S2 . S3. S4i occurs. The signal S1 nopulse width or duty ratio is determined by the humidity sensing element 9.
This can be achieved by setting a value that does not cause characteristic changes or deterioration, and by reducing the pulse width or keeping the repetition frequency low.

Here, the waveforms of the signals S+ and S2 are made so that they do not overlap each other as shown in FIG.

The aforementioned signal 31i is connected to the input terminal of an operational amplifier 2 having a resistor 10 as an input resistance and a humidity sensing element 9 as a current feedback element, and a signal S2i as an input resistance.
are respectively applied to the power terminals of the operational amplifier 3 which also has a resistor 12 as a current feedback element.

Here, the peak values of the output voltage v1 of the operational amplifier 2 and the output v2 of the operational amplifier 3 are as follows.

However, here, all the peak values of signal 8+ and S2 are Vs
shall be.

In addition, if the absolute value of the peak value of output v1 is '1V1p, and the absolute value of the peak value of output v2 is @V2 p, then Vl
p.

v2p is represented by the following equation), (81).

v, , -Rs Vs , , , , , , , ,
,,,,,−,,,,,0,,,,,,,,,,,,,,,
(7) 1 R5・Vs V21) =□・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・(8)2 The aforementioned output voltages V1 and V2 are resistors 13 and 14'i
The current is then supplied to the amplifier 4 as a current I.

Amplifier 4 operates as a nonlinear amplifier by using diode 8 as a current feedback element.

The output voltage v3 of the amplifier 4 has the waveform shown in FIG.
The peak value is a value obtained by logarithmically transforming vlp and V2pi alternately.

Here, in FIG. 2, the absolute value of the current I and the current flowing through the diode 8 is equal, and the forward voltage drop of the diode is V.
The relationship between F and electric current can be expressed by the following equation.

0 or Takashi: Diode current (MU) IO: Proportional load (MU) k: Boltzmann constant (JloK) T: Temperature (0K) q: Electron charge (C) Voltage memory 6.6 is a pulse Signal Ss from controller 1,
84, and the output v5 of the operational amplifier 4 is stored.

The signals 83 and 84 from the pulse controller 1 are output after the waveform of the output v3 becomes stable, as shown in FIG.

The signal 83 is designed to maintain an arbitrary phase difference with the saline signals S1 and 82.

The output y4 of the voltage memory device 6 can be expressed by Equation (7) and Equation (10) F.

Further, the output voltage v5 of the voltage storage device 6 can be expressed by equation (8).

The aforementioned output voltages V4 and Vs are applied to the arithmetic unit 7.

After being calculated there, the output voltage Vout is output to the output terminal 16.
obtained as. , FIG. 4 is a circuit diagram showing an example of the configuration of the arithmetic unit 7.

In the figure, input voltages V4 and Vs are applied to a subtracter 26 consisting of an amplifier 21 and resistors 22-25.

Here, assuming that the values of the resistors 22 to 26 are all equal, the output voltage v6 of the subtracter 26 is expressed by the following equation (13).

V6 = V4- Vs ・・・・・・・・・・・・
・−・・・・・・・・・・・・・・・・(13) Here, by substituting k into equation (11) and equation (1-2), the following equation is obtained.

Here, R11・R13:=R1o・R14, Ro=R1
z, equation (6) and equation (14) #) v6 is V6 = tan(-AH-B'Δt) -1------1-1
−(15). This output voltage v6 is the output voltage v5
It is also supplied to the divider 27. The divider 27 is 2
7, and KD is the proportionality constant between the input terminals of the divider 27.

Output voltage v77 Equation (12) and Equation (16) KD@V6 5 In Equation (16), Δt is Δt−7−TO from Equation (2).
There is a, KD and. , n (two-anal source-one) is.

R11R13I.

,fah,. A, K. , -1°7. . , 2ㅅ1).

Substituting this into equation (16) yields the following equation.

13,,-.

V7=KD'(-AH-B'T-1-B' To
) - (17) Input the aforementioned outputs Vy, Vs and the output Vc of the constant voltage source to the adder. Adder 2
8 is three input resistors 29, 30, 31 and current feedback resistor 3
2 and an operational amplifier 33. In addition, resistance 2
9,30°31.32 values R29 and Rso respectively
4 R31.

It is set as R52.

Here, the output Vout of the operational amplifier 33 can be expressed by the following equation.

Substituting equation (12) and equation (17) into equation (18) yields a linear equation.

(19) In equation (19), settings are made so that the relationship of R31f following equation holds true.

4 Also, settings are made so that the relationship of R29 and Vc'i+the following equation holds true.

Substituting equations (20) and (21) into equation (19) gives Vout −□ ・・・・・・・・・・・・・・・・・・
...(22) Rs.

becomes.

The following formula is obtained.

Vout Nim tH・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・(23) 5′: Proportionality constant (V/%) H: Relative humidity (%) The output You t of the humidity detection device is expressed by formula (23) and is independent of temperature. And its output Vo
ut is proportional only to relative humidity.

1571. -, :, As is clear from the above description, the humidity detection device according to the present invention uses an electric resistor as a solid detection element for humidity and temperature, and uses the solid detection element and reference resistor as a current feedback element. a nonlinear amplifier that uses a diode as a current feedback element; a voltage memory that stores the output voltage of the nonlinear amplifier at two different times by inputting a control pulse; and a voltage memory that stores the output voltage of the nonlinear amplifier at two different times. A computing unit that performs → calculations using the output voltage of the unit.

and a pulse controller that alternately inputs pulse voltages to the two amplifiers and generates control pulses for the voltage memory, and outputs of the two amplifiers to the nonlinear amplifier. By adding this, a humidity detection signal that has been subjected to all five temperature corrections is output. Thereby, deterioration and change in characteristics of the humidity sensing element can be prevented, and a highly reliable humidity sensing device can be realized. Humidity detection output is proportional to relative humidity, making it convenient for display and recording, and easy to connect with other devices.In addition, it is a low-cost device that can serve as both a temperature detection circuit and a logarithmic conversion circuit. of

[Brief explanation of the drawing]

Fig. 1 is a humidity characteristic diagram of a humidity sensing element used in an embodiment of a humidity detection device according to the present invention, Fig. 2 is a block diagram of this embodiment, Fig. 3 is a timing chart of Meng, and Fig. 4 1 is a circuit diagram showing seven examples of arithmetic units used in this embodiment. 1... Pulse controller, 2, 3.4...
Arithmetic amplifier, 5.6...Voltage memory, 7...
...Arithmetic unit, 8...Diode, 9...
・・Humidity detection element, 10, 11゜12.13.14・
·····resistance.

Claims (3)

[Claims] (1) Two amplifiers that use a resistor whose electrical resistance changes depending on humidity and temperature as a solid-state sensing element, use the solid-state sensing element and a reference resistor as a current feedback element, and a nonlinear amplifier that uses a diode as a current feedback element. an amplifier, and a voltage memory that stores the output voltage of the nonlinear amplifier at two different times by inputting a control pulse;
a computing unit that performs bone-bone calculations using the output voltage of the voltage memory; a pulse controller that alternately inputs pulse voltages to the two amplifiers and further generates control pulses for the voltage memory; f: A humidity detection device characterized in that it has a temperature-corrected humidity detection signal by adding the outputs of the two amplifiers to the nonlinear amplifier. (2) The humidity detection device according to claim 9, wherein the solid state detection element is made of a porous metal oxide ceramic resistor. (3) The humidity detection device according to claim 1, wherein the solid state detection element is made of a porous magnetic resistor containing MgCr2O4f. .