JPH02120660A - Humidity sensor - Google Patents

Abstract

PURPOSE:To obtain a humidity sensor having good accuracy and a high response speed over a long period of time by operating relative humidity on the basis of the absorption quantity of an ultrasonic wave and temp. CONSTITUTION:The ultrasonic wave from a transmitter 2a is received by a receiver 2b and absorbing quantity alpha in air is calculated on the basis of preset and inputted standard data by a microcomputer 6. Temp. data is successively applied to the microcomputer 6 in predetermined timing from a temp. detector 7 for detecting the temp. in a humidity detection region. Relative humidity is operated on the basis of this temp. data and the absorbing quantity alpha. By this method, humidity can be measured over a long period of time with good accuracy and can be also measured rapidly without exerting a measuring condition on a response speed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic humidity sensor that detects humidity by utilizing the change in the amount of absorption of ultrasonic waves propagating in the air depending on temperature and humidity. .

As conventionally known humidity sensors, there are a first type that measures humidity by changes in electrical resistance, and a second type that measures humidity by changes in capacitance.

These humidity sensors are configured to measure humidity by detecting a change in resistance or a change in capacitance due to physical or chemical adsorption of water molecules onto a sensor detection section. A representative example of the first type is a humidity sensor that measures changes in the conductivity of ceramics, and a representative example of the second type is a humidity sensor that measures changes in the capacitance of polymer membranes. .

However, both of the above two types of humidity sensors have the following drawbacks, which limit their ability to perform accurate measurements over a long period of time.

■Due to adsorption of water molecules, moisture-sensitive materials such as ceramics and polymer membranes may be ionized and denatured (deteriorated over time), requiring troublesome cleaning (refreshing) work.

■Since the response speed (responsiveness) of the sensor detection part is controlled by the adsorption speed of water molecules, the sensor detection part will be unable to follow these changes in situations where the humidity changes rapidly, that is, the adsorption speed changes rapidly. .

The present invention was made in order to eliminate the drawbacks of the conventional technology, and an object of the present invention is to provide an ultrasonic humidity sensor that can perform accurate measurements over a long period of time without cleaning the sensor detection section. .

Another object of the present invention is to improve response speed.

The humidity sensor according to the present invention includes an ultrasonic transmitter and an ultrasonic sensor disposed in the ultrasonic transmitter to detect ultrasonic waves emitted from the transmitter and propagating in the air. A sonic receiver, a temperature detector that detects the temperature of this detection system, and a relative that has a certain relationship with these values based on the absorption amount determined from the detection results of the ultrasonic receiver and the detected temperature of the temperature detector. It is characterized by comprising a calculator that simulates humidity and calculates relative humidity based on the simulation results.

When necessary, humidity can be measured simply by detecting ultrasonic waves propagating in the air and running a simulation, so there is no need to introduce water molecules into the sensor detection section. , the negative effects of this can be eliminated.

L-Zen One embodiment of the present invention will now be described in detail based on the drawings. FIG. 1 is a block diagram showing the overall configuration of a humidity sensor according to the present invention, and FIG. 2 is a graph showing the relationship between absorption amount and relative humidity using detected temperature as a parameter.

An ultrasonic sensor 2 is provided in the humidity detection area.

This ultrasonic sensor 2 includes a transmitter 2a connected to an oscillator l.
and a receiver 2b placed opposite to the transmitter JH2a with an interval of, for example, 0.5 m.
), the transmitter 2a emits an ultrasonic wave, which is detected by the receiver 2b.

Here, the energy of the ultrasound propagating through the opposing space is absorbed and attenuated by air, which is a medium intervening in the space, and the sound pressure level (dB) of the ultrasound after absorption and attenuation is sent to the receiver 2b as a detection signal. It will be detected.

A waveform shaper 3 for shaping the waveform of the detection signal is connected to the receiver 2b, and a low-pass filter 4 is connected to the waveform shaper 3. The low-pass filter 4 removes noise components having a higher sound pressure level than the detection signal, and inputs a signal containing no noise components to the microcomputer 6 via the A/Dit*2s 5.

Standard data for calculating the absorption amount α in the air using human input signals is preset and input into the microcomputer 6, and the absorption amount α is calculated based on this standard data and the input signal. Further, temperature information is sequentially given to the microcomputer 6 at a predetermined timing from a temperature detector 7 (for example, a thermistor) that detects the temperature in the humidity detection area, and this temperature information and the absorption Based on this, a simulation as shown in Fig. 2 is executed to calculate the relative humidity (%).In this way, the relative humidity in the detection area is measured.

The obtained measurement results are then displayed on a display (not shown) or output to a recording device such as a printer.

However, in Figure 2, the vertical axis shows absorption α, and the horizontal axis shows relative humidity.
This is a graph showing the relationship between the two at various detected temperatures (set temperatures), and by detecting the temperature 1゛ [0C] and the absorption amount α based on this graph, that is, the simulation result, the relative humidity can be calculated. I know that it will happen.

Note that the emission shown in FIG. 2 is based on the ultrasonic sensor 2.
The results are shown when the oscillation frequency is 1000 KHz and the separation distance between the transmitter 2a and receiver 2b is 50 cn+.

This measurement principle will be briefly explained below.

First, the absorption amount α is the sum of the classical absorption αe and the relaxation absorption αr, and the classical absorption α is expressed by the following equation 0.

α, t=5.578xlO-9x(T/To)/(T
+To)
OK), and To is the absolute temperature (= 293.15°K
]. P is the saturated water vapor pressure at room temperature (kg/a
n"), which is detected by a pressure detector (not shown) and input to the microcomputer 6. Po is the saturated water vapor pressure in the standard state, and is preset and input to the microcomputer 6. This is the oscillation frequency (KHz) of the oscillator l.Therefore, the classical absorption α is immediately calculated based on the temperature information from the temperature detector 7.

Further, the relaxation absorption αr is the sum of the relaxation absorption αr0 of oxygen and the relaxation absorption αrN of nitrogen, and the relaxation absorption αre and the relaxation absorption α are expressed by the following formulas (1) and 0, respectively.

αr62Ao f”/ (fro+ (r2/r, o
) l...■αrN=ANf”/ (frs+
(f2/frs) )...■However, ",i f□
is the relaxation frequency of oxygen and nitrogen in relaxation absorption, and AOlAM is the attenuation amount of ultrasound in oxygen and nitrogen [
dB), and are shown by the following formulas (■) and 0, respectively.

Ao =0.01278(T/To)””xexp
(2329/T)・・・■AN=0.2069(T/To)””Xexp
(3352/T)・・■ Here, AOSAN is immediately calculated based on the temperature information from the temperature detector 7 according to the formula ■ and 0, but fro and frN are unknown values. However, the absorption amount α is obtained as described above, and the relaxation absorption αr is obtained by subtracting the classical absorption αcl from this value, resulting in the relaxation absorption α′., relaxation absorption αrH and fro
, ``, 8, frQs
The value of frN can be found.

Therefore, it can be theoretically understood that the relative humidity can be calculated by executing a simulation using the above 0-0 formula.

When calculating relative humidity using the above simulation, the temperature information required for the simulation is updated sequentially to the latest information, so measurement errors caused by temperature changes can be canceled by 4°, improving accuracy. This allows for good humidity measurements.

In the case of the present invention of 1 q or more, the ultrasonic receiver No. 13 detects the absorption layer of the ultrasonic waves propagating in the air, sequentially detects the temperature in the detection system, and calculates these detected values. Since the configuration is such that a simulation is executed based on the above and the relative humidity is calculated, unlike the above-mentioned conventional sensor, water molecules and the like that adversely affect measurement accuracy and response speed are not adsorbed. Therefore, accurate measurements can be maintained over a long period of time, and the response speed is not affected by measurement conditions, so rapid and accurate measurements can be performed even in environments where humidity changes rapidly. It turns out.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of a humidity sensor according to the present invention, and FIG. 2 is a graph showing the relationship between the amount of ultrasonic absorption in the air and the relative humidity using measured temperature as a parameter. 2... Ultrasonic sensor, 2a... Transmitter, 2b...
Receiver, 6... microcomputer. Patent applicant Mura Co., Ltd. [11 Seisakusho]

Claims (1)

[Claims] (1) The ultrasonic transmitter is placed opposite the ultrasonic transmitter, and the signals emitted from it,
An ultrasonic receiver that detects ultrasonic waves propagating in the air, a temperature detector that detects the temperature of this detection system, and an absorption amount determined from the detection results of the ultrasonic receiver and a detected temperature of the temperature detector. 1. An ultrasonic humidity sensor comprising: a computing unit that simulates relative humidity having a certain relationship with these values based on the above values, and calculates the relative humidity based on the simulation results.