JPH0712769A - Hygrometer - Google Patents

Abstract

PURPOSE:To provide a hygrometer capable of accurately detecting humidity with quick responsiveness, independent of ambient temperature, and ensuring freedom from the dispersion of heater resistance. CONSTITUTION:This hygrometer has a resistance measuring circuit 1 for measuring the resistance value of a heater 13, an arithmetic circuit 2 for finding a difference between a measured value and a theoretical value, and a memory information circuit 3 for storing relationships between a resistance value and temperature, between a resistance value and electric power, and between a resistance value and absolute humidity. Furthermore, a difference between a rise in resistance value resulting from the actual application of required power to the heater 13 and a rise in theoretical resistance value available from the assumed application of the required power is obtained, and an actual measurement resistance value and humidity to be added are thereby found.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hygrometer, and more particularly to a hygrometer that raises the temperature detected by a resistor to determine the humidity by changing the resistance value.

[0002]

2. Description of the Related Art Gas detectors, for example, semiconductor gas detectors, utilize the fact that a heated metal oxide semiconductor, for example, SnO ₂ , reacts with a reducing gas to reduce its resistance value. It is designed to detect.

FIG. 4 is a configuration diagram for explaining an example of a gas detector formed in a cantilever structure to which the present invention is applied. FIG. 4 (a) is a plan view and FIG. 4 (b) is B of FIG. 4 (a)
-B line sectional drawing, in the figure, 10 is a substrate, 11 is the substrate 10
2 is a thin film insulator of a silicon chip formed on the substrate 10, and the thin film insulator 12 is a cantilever-shaped overhanging portion of the silicon thin film insulator or the concave portion of the concave portion. The bridge portion 12 is bridged in a double-supported beam type, and the heater 13 and the gas detection element 14 are provided on the overhang portion or the bridge portion 12 in the vicinity of the heater 13. The gas detection element 14 is specifically a metal oxide semiconductor of SnO ₂ as described above. The concave portion 11, the projecting portion 12, the resistance heating element portion 13, and the gas detecting portion 14 are preferably formed on the same substrate 10.

When performing gas detection, the heater 13 is heated with a constant power regardless of the ambient temperature depending on the gas to be detected, and gas detection is performed by the change in resistance of the gas detection element 14. .

[0005]

However, according to the above-mentioned prior art, since the gas detection element is provided in addition to the heater for detecting the gas, the cost is increased, and the detection temperature varies depending on the detection gas, so that the ambient temperature is different. You must also consider the difference between.

[0006]

In order to solve the above-mentioned problems, the present invention provides (1) a hygrometer which raises the temperature detected by a resistor and detects the humidity by the resistance value at the temperature. A power control circuit, a circuit for measuring the resistance value of the resistor, a theoretical resistance value obtained by adding constant power to the resistance value of the ambient temperature, and an actually measured resistance value after adding constant power from the theoretical resistance value. And a memory information circuit that stores the relationship between the difference between the logical resistance value and the measured resistance value and the added power and absolute humidity, and (2) In (1) above. A memory information circuit that stores the relationship between the resistance value and the temperature and the relationship between the temperature and the saturated vapor pressure, and the arithmetic circuit that calculates the relative humidity from the temperature, the absolute humidity, and the saturated vapor pressure. is there.

[0007]

Function: A constant power is applied to a resistor (hereinafter referred to as a heater) to raise the temperature of the heater by a constant temperature regardless of the ambient temperature, and the absolute humidity is obtained from the change in the resistance value at that time. Further, the atmospheric temperature and the saturated water vapor pressure are obtained from the resistance value of the atmospheric temperature, and the relative humidity is also obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a diagram for explaining the operating principle of the present invention. In the figure, R _H01 and R _H02 each have an ambient temperature of 20.
It shows the resistance value of the heater 13 at the temperature of 40 ° C. Then, a constant power P is applied to the heater 13 to heat it. When the electric power P is applied to the heater 13, the temperature rises by T ° C. due to self-heating. This rising temperature T ° C. is determined by the heat capacity of the heater 13 and the applied power P, and is not affected by the ambient temperature. At this time, the heater 1
3 is, of course, a well known equation for resistors, R = R ₀ + α
The resistance value increases due to ΔT. That is, assuming that the resistance values at the current temperature are R _H01 and R _H02 , respectively, the temperature is T
Resistance values Rs ₁ and Rs ₂ as theoretical values when the temperature rises by
The values should be s ₁ = R _H01 + αT and Rs ₂ = R _H02 + αT. However, when actually measured, the value does not match the theoretical value. That is, the measured value R _H1 after the power P is added to R _H01 and the measured value R _H2 after the power P is added to R _H02 are
The value is ΔR lower than the theoretical values Rs ₁ and Rs ₂ . This difference ΔR
Has a correlation between the absolute humidity in the atmosphere and the applied power P. The present invention has been made with this in mind.

FIG. 1 is a diagram for explaining one embodiment of the present invention, in which 1 is a resistance value measuring circuit, 2 is an arithmetic circuit, and 3 is a circuit.
Is a memory information circuit, and 4 is a power control circuit. FIG. 2 is a flow chart for explaining the operation of the circuit of FIG.
A description will be given based on each step of this flowchart.

Step 1 : The resistance value measuring circuit 1 measures the resistance value R _H0 at ambient temperature (hereinafter referred to as the initial value R _H0 ).
At this time, measurement is performed with a small current so that the heater 13 does not self-heat and the temperature of the heater 13 does not rise due to the current flowing through the resistance to be measured. step2 : The calculation circuit 2 is the heater 13 from the power control circuit 4.
The theoretical resistance value Rs of the heater 13 when the electric power P is applied is Rs =
It is calculated from R _H0 + αT (α: a value determined by the heater 13). step3 : The power control circuit 4 applies a constant power P to the heater 13. step 4 : The resistance value measuring circuit 1 measures the resistance value R _H1 of the heater 13 after applying the electric power P (hereinafter, referred to as an actual measurement value R _H1 ). step 5 : The arithmetic circuit 2 obtains the difference ΔR (Rs−R _H1 ) between the theoretical value Rs and the measured value R _H1 . step6 : In the storage information circuit 3, the absolute humidity D is obtained from the table of the absolute humidity D determined by the applied power P and the resistance value difference ΔR. If the absolute humidity D is acceptable, the output is ended and the relative humidity H is obtained. step7 : The memory information circuit 2 contains a table of the ambient temperature t and the initial resistance value R _H1, and the ambient temperature t is determined from the initial resistance value R _H1 . The stored information circuit 2, there is also a table showing the relationship between the ambient temperature t and the saturated water vapor pressure e _S, determining the saturation vapor pressure e _S than the ambient temperature t. step8 : The arithmetic circuit 2 calculates the relative humidity from the following equation (1) and then outputs it.

[0011]

[Equation 1]

Although the present invention obtains each humidity by using the resistance value difference ΔR as a parameter, the present invention is not limited to this, and ΔT is obtained from the equation R = R ₀ + αT.
May be a parameter, or ΔE, Δ can be calculated from the equation of E = IR.
I may be used as a parameter.

[0013]

【effect】

(1) Effect on claim 1: Since a predetermined electric power is applied to the heater, the resistance value of the heater is measured, and the absolute humidity is measured, a gas sensitive element is not required, which leads to cost reduction and is naturally affected by ambient temperature. I don't have to. (2) Effect on claim 2: Absolute humidity can be converted to relative humidity by determining the ambient temperature from the resistance value of the heater.

[Brief description of drawings]

FIG. 1 is a circuit diagram for explaining an embodiment of the present invention.

FIG. 2 is a flowchart illustrating an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between resistance value and temperature.

FIG. 4 is a diagram for explaining a conventional technique.

[Explanation of symbols]

1 ... Resistance value measuring circuit, 2 ... Arithmetic circuit, 3 ... Memory information circuit, 4 ... Constant power output circuit, 10 ... Substrate, 11 ... Recessed portion, 1
2 ... Overhanging portion, 13 ... Heater, 14 ... Gas sensitive element.

Claims (2)

[Claims] 1. A hygrometer that raises a temperature detected by a resistor and detects humidity by a resistance value at the temperature, a resistor, a power control circuit, a circuit for measuring a resistance value of the resistor, and an atmosphere. Between a theoretical resistance value obtained by adding constant power to the resistance value of temperature and a difference between the theoretical resistance value and the measured resistance value after adding constant power from the theoretical resistance value; and the logical resistance value and the measured resistance value. A hygrometer having a storage information circuit that stores the relationship between the difference, the added power, and the absolute humidity. 2. The storage information circuit according to claim 1, which stores the relationship between the resistance value and the temperature and the relationship between the temperature and the saturated vapor pressure, and the arithmetic circuit which calculates the relative humidity from the temperature, the absolute humidity, and the saturated vapor pressure. A hygrometer characterized by having.