JPS6152945B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention uses a temperature/humidity detection device, particularly a solid state temperature/humidity detection element whose electrical resistance value changes depending on humidity and whose capacitance value changes depending on temperature. The present invention relates to a highly accurate temperature/humidity detection device.

Currently, there are many solid-state humidity sensing elements, and most of them are solid-state humidity sensing elements that can be formed into solid-state circuits. Among these humidity sensing elements, the electrical resistance of the element changes due to adsorption or adhesion of moisture in the surrounding air, and if a DC voltage is applied for a long time, it will change due to electrolysis,
Since the characteristics may change or the element itself may deteriorate, it is usually used by applying an alternating current voltage.

In addition, the characteristics of many of these solid-state humidity sensing elements change not only with humidity but also with temperature, so
In order to accurately detect humidity, a temperature detection element has been used to perform temperature correction.

The present invention calculates the resistance value and capacitance value by applying two alternating current signals with different frequencies to a temperature/humidity sensing element whose electrical resistance value changes with humidity and whose capacitance value changes with temperature. This realizes a temperature/humidity detection device that determines temperature-corrected humidity and humidity-corrected temperature.

Hereinafter, one embodiment of the present invention will be described in detail using the drawings. FIG. 1 shows the humidity characteristics of the resistance value of the solid-state temperature/humidity sensing element used in this example. Furthermore, FIG. 2 shows the temperature characteristics of the capacitance value of the sensing element.

From FIG. 1 and FIG. 2, the characteristics of the temperature/humidity sensing element are shown by the following two equations, respectively.

R=Roexp{B(1/T-1/To)}exp(-AH)...
(1) C=-αT+βH+γ...(2) However, T: Ambient temperature (〓), To: Reference temperature (〓) H: Relative humidity (%), B: Temperature coefficient (〓) A: Humidity coefficient (1) /%) R: Resistance value of the element (Ω) Ro: Resistance value when T=To〓, H=0% (Ω) C: Capacitance value of the element (pF) α, β, γ: Depends on the element Determined constant Therefore, the above temperature/humidity sensing element is equivalent to a parallel circuit of passive elements shown by equations (1) and (2).

FIG. 3 shows the frequency characteristics of the capacitance value of the sensing element, and in the low frequency region, it is greatly affected by humidity on the high humidity side. Therefore, capacitance measurement must be performed at a sufficiently high frequency (for example, 300 KHz or higher).

FIG. 4 is a block diagram of this embodiment. In the figure, 1 is an oscillation circuit, 2 is a frequency divider circuit, 3 is a selection circuit that selects either the output of the oscillation circuit 2 or the output of the frequency divider circuit 2, and C is the DC component of the output of the selection circuit 4. 4 is a solid temperature/humidity sensing element with a heater H, Rs and Cs are fixed resistors and capacitors connected in series with the sensing element 4, 5 is a rectifier circuit, 6 is a hold circuit, 7 is a Analog-digital converter (A/
D converter), 8 is an arithmetic circuit which outputs temperature information and humidity information from terminals _T1 and _T2 , respectively. Note that 9 is a control circuit.

The functions of the embodiment shown in FIG. 4 will be explained using FIG. 3. The frequencies of the output of the oscillation circuit 1 and the output of the frequency dividing circuit 2 are determined as follows.

(1) The output frequency of the oscillation circuit 1 is such a high frequency that the capacitance value of the sensing element 4 has no humidity dependence as shown in Fig. 3, and the minimum resistance within the measurement temperature range and measurement humidity range. than the value
Select so that the impedance value due to element capacitance is sufficiently small.

(2) The output frequency of the frequency dividing circuit 2 is set to a low frequency such that the impedance due to the capacitance of the sensing element 4 is sufficiently larger than the element resistance value.

The control circuit 9 connects the output of the frequency dividing circuit 2 via the selection circuit 3 to a series connection body of the solid temperature/humidity sensing element 4 and a parallel circuit consisting of a fixed resistor RS and a capacitive element Cs, and to a capacitor C. Therefore, the DC component is removed and supplied. The divided voltage at point P at that time
Vo is expressed by the following formula, where the applied voltage is V.

Vo=Rs/R+RsV ……(3) This equation (3) is based on equation (1) So, by rearranging, we get the following formula.

B/T-B/To-AH=l _o {V-Vo/Vo・Rs
/Ro}...(4) Next, the control circuit 9 supplies the output of the oscillation circuit 1 to the series connection body via the selection circuit 3. The divided voltage Vo at point P at this time is It can be expressed as However, ω is the output angular frequency of the oscillation circuit 1. From equations (5) and (2), −αT+βH=Vo/V−VoCs−γ (6). By combining equations (4) and (6), Here, C=Vo/V-VoCs-γ D=l _o {V-Vo/Vo Rs/Ro}+B
/To is found. Also, the humidity H is calculated from equation (4). It can be found by substituting the temperature T obtained from equation (7) into .

Therefore, the outputs of the oscillator circuit 1 and the frequency divider circuit 2 obtained by dividing the output of the oscillator circuit 1 are applied alternately via the selection circuit 3, and the divided voltage Vo at the point P at that time is converted to DC by the rectifier circuit 5. After conversion, the temperature and humidity can be determined by holding the data in the hold circuit 7 and digitally converting it in the A/D converter 7 and calculating it according to equations (7) and (8). The control circuit 9 holds and resets the selection circuit 3 and the hold circuit 6,
It also controls the arithmetic circuit 8.

Moreover, the above-mentioned solid-state temperature/humidity detection element must be used while being exposed to the air due to its nature. Therefore, not only moisture in the air but also various other substances adhere to the surface of the solid-state temperature/humidity detection element, reducing its sensitivity to humidity. Therefore, in this embodiment, as shown in FIG. 4, the control circuit 9 controls the solid temperature/humidity sensing element 4 at regular intervals by the heater H placed near the sensing element to Substances attached to the element surface are removed by heating to .degree.

As described above, the present invention has the following effects.

(1) Temperature and humidity can be measured with high precision using only a single sensing element, without the need for temperature or humidity compensation elements.

(2) Since the circuit configuration is simple and there is only one sensing element, it is easy to implement.

(3) Most of the circuit configuration can be integrated into ICs.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the humidity characteristics of the resistance value of the solid-state temperature/humidity sensing element used in the embodiment of the present invention;
FIG. 2 is a diagram showing the temperature characteristics of the capacitance value, and FIG. 3 is a diagram showing the frequency dependence of the capacitance value. FIG. 4 is a block diagram of a temperature/humidity detection device which is an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Oscillation circuit, 2... Frequency division circuit, 3... Selection circuit, 4... Solid temperature/humidity sensing element, 5... Rectifier circuit, 6... Hold circuit, 7... A/D converter, 8 ...Arithmetic circuit, 9...Control circuit, H...
...Heater, C...Capacitor, Rs...Fixed resistor, Cs...Capacitor.

Claims (1)

[Claims] 1 Using a solid-state temperature/humidity detection element whose electrical resistance value changes according to humidity and whose capacitance value changes according to temperature, and whose humidity dependence of the capacitance value exhibits a frequency characteristic, A temperature/humidity detection circuit consisting of a humidity detection element and a parallel circuit of a fixed resistance element and a fixed capacitance element is supplied with two alternating current signals at a frequency where the capacitance value of the detection element shows humidity dependence and a frequency where it does not. is selectively applied to measure the voltage at the connection point of the solid-state temperature/humidity sensing element and the parallel circuit, thereby detecting the electrical resistance value and capacitance value of the solid-state temperature/humidity sensing element; A temperature/humidity detection device characterized by calculating temperature and humidity from values.