JPH03138557A - Humidity measuring instrument - Google Patents

Abstract

PURPOSE:To eliminate the need for calibration which uses special equipment by detecting the output variation of a humidity detecting element which is driven at two frequencies separately as resistance variation information and capacity variation information and providing a detector itself with a function which outputs the quantity of deterioration. CONSTITUTION:Signals of frequencies f1 and f2 from 1st and 2nd frequency generation parts 2 and 3 are switched by a switching circuit 4 and inputted to a humidity detecting element 1. Signals from a temperature detecting element 5 and a humidity detecting element 1 are inputted to a humidity arithmetic part 6 to calculate humidity and detect deterioration. The humidity detecting element 1 is driven at the 1st and 2nd frequencies f1 and f2 and the output variation of the humidity detecting element 1 is detected separately as the resistance variation information and capacity variation information. Capacity variation due to deterioration different from basic capacity variation by water adsorption and desorption is detected from dielectric constant variation due to the sticking of a contaminant on a humidity sensing film and porosity and pore diameter variation due to the corrosion of the humidity sensing film by using variation between the outputs of the humidity detecting element 1 when the element is driven at the 1st and 2nd frequencies, thereby detecting the deterioration.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a humidity measuring device, and particularly to a humidity measuring device capable of outputting the amount of deterioration of a humidity detecting element.

(b) Conventional technology In general, resistance-type or capacitance-type humidity sensors are used as sensors (elements) in humidity measuring devices, and output signals according to resistance or capacitance values that change depending on humidity. Humidity is measured based on the signal.

For example, in a resistance-type humidity sensor, the moisture-sensitive membrane is made of porous ceramics, and the pores contain moisture (moisture) in the atmosphere.
As the electrolyte is adsorbed and condensed, an electrolyte is formed on the inner surface of the pores and the resistance value changes, and by AC drive, a signal corresponding to the change in resistance value is output. This type of humidity sensor can handle hydrophilic and hydrophobic substances such as tobacco and oil mist, and corrosive substances such as acids. η leakage affects the moisture-sensitive film, and its properties change due to erosion and chemical changes, increasing measurement errors. For this reason, in the past, calibration was performed periodically using a humidity generation tank and a hygrometer for calibration, and if the measurement error was extremely large, the element was assumed to have deteriorated and replaced.

(c) Problems to be Solved by the Invention Conventional humidity measuring devices do not have a function to detect the deterioration of the humidity detecting element, so as described in Section 2, a humidity generating tank and a hygrometer for calibration are required. used and had to be calibrated regularly. Therefore, it is necessary to prepare equipment for calibration, and the calibration must be performed periodically, which is complicated.

Furthermore, there is a problem in that if the element deteriorates between calibrations and the next calibration, measurement errors occur during that period.

This invention has been made in view of the above-mentioned problems, and aims to provide a humidity measuring device that does not require calibration using special equipment by providing the detection device itself with a function to output the amount of deterioration. The purpose is

(d) Means and operation for solving the problems The humidity measuring device of the present invention includes a humidity detecting element, a first driving section that drives the humidity detecting element at a first frequency, and a humidity detecting element that drives the humidity detecting element at a first frequency. a second driving section that drives at a second frequency higher than the first frequency; a switching section that switches between the first driving section and the second driving section to connect to the humidity detection element; and the first driving section. means for measuring humidity based on the output of the humidity detecting element when driven by the first drive section and the second drive section; and detecting the amount of deterioration of the humidity detecting element based on the output of the humidity detecting element during each drive by the first drive section and the second drive section. It is characteristically equipped with the means to do so.

As shown in Figure 3, the equivalent circuit of the humidity sensor includes the resistance RX of the electrode, the bulk resistance Rs of the humidity sensitive membrane, the bulk capacitance CS of the humidity sensitive membrane, the ion transfer component R8 due to moisture adsorption,
It can be expressed as capacitance CN due to moisture adsorption. The equivalent resistance R and capacitance C of the humidity sensor are shown in Fig. 4, where the characteristic change due to deterioration is a change in the resistance component, as shown by the solid line at the initial stage and the broken line at the time of deterioration, as shown in Figure 4. can be replaced by the change in capacitance component (
The resistance RA and capacitance CA in FIG. 3 each indicate changes due to their deterioration. ).

Therefore, in this invention, the humidity sensing element is connected to the first (fundamental) frequency (e.g. f + = 100) 1z) and the second
frequency (e.g. f2=50KHz or 100KH
z), and detects the output change of the humidity detection element by separating it into resistance change information (during r+ driving) and capacitance change information (during f2 driving), and detects the dielectric constant due to dirt substances adhering to the moisture sensitive membrane. Changes in capacitance due to deterioration, which are different from basic capacitance changes due to moisture adsorption and desorption, due to changes in porosity and pore diameter due to moisture-sensitive membrane erosion, etc., when driven by the first frequency and when driven by the second frequency. Deterioration is detected by detecting a change in the humidity detection element output.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a block diagram of a humidity measuring device showing an embodiment of the present invention. This humidity measuring device has a humidity detecting element 1
, a first frequency generator 2 that generates a signal with a first frequency f1 (50Hz), and a second frequency f2 (50Hz).
A second frequency generating section 3 that generates a signal of 0 KHz- or 100 KHz, and a humidity detecting element 1 that switches between the signals of the first frequency f1 or the second frequency f2.
a switching circuit 4 for inputting and driving the temperature detecting element 5; a humidity calculating section 6 for taking in signals from the temperature detecting element 5 and the humidity detecting element 4, calculating humidity, and detecting deterioration; A first storage unit 7 that stores a characteristic flB indicating the relationship between resistance (impedance) and humidity at frequency "1" at an initial time without deterioration, and a characteristic f indicating a relationship between resistance (impedance) and humidity at frequency f2 at an initial time without deterioration.
2B, a frequency selection control section 9 that controls switching of the switching circuit 4, a humidity display section 10 that displays the humidity H output from the humidity calculation section 6, and a humidity calculation section 6 that also stores the humidity H. and a humidity deterioration amount display section 11 that displays the humidity deterioration amount ddH output from the humidity deterioration amount ddH.

Next, the deterioration detection operation in the humidity measuring device of the above embodiment will be described with reference to the characteristics of the output of the humidity detecting element 1 shown in FIG. 2, that is, the resistance RX and the measured humidity I.

As mentioned above, capacitance changes exist due to deterioration other than capacitance changes due to moisture adsorption and desorption. Therefore, here, the capacitance change due to this deterioration is detected by second frequency driving to detect the deterioration.

First, the initial drive characteristics by the signals of the first frequency f1 and the second frequency f2 are flBsf2B, and the characteristics after deterioration are flA and f2A, which are shown in FIG.

Among these, the initial characteristics ran, rzl+ are stored in the first storage unit 7,
If it is stored in the second storage unit 8 and there is no deterioration,
The temperature F (X) corresponding to the intersection with the characteristic ran corresponding to the resistance RX of the humidity detection element 1 is output as the measured humidity H.

Now, the humidity detection element 1 has deteriorated, and the first frequency f after deterioration
, the driving characteristic is flA, the second frequency f after deterioration,
Let the characteristic due to canter be f2A. Here, at humidity H, if the resistance value at the first frequency f1 drive moves from point 0 to point a due to deterioration, then the conversion process of the humidity value is performed using the reference characteristic r18, so the point a is determined to be the point 1) of the same resistance on the characteristic f+n,
The humidity value is assumed to be ■1□. Therefore, dH-H, -H, (%
R, H) becomes the error and becomes the amount of deterioration. If there is no change in capacitance before and after deterioration, the characteristic rz at humidity H1
Characteristic f21 corresponding to the 0 point of A and the same temperature Fiz as point b
It should match the resistance value of point 0 (resistance value of point d) of 1. However, in reality, the capacitance changes due to deterioration.
4F and the characteristic after deterioration of 2 at the second frequency rzn changes more than the characteristic before deterioration f2B, so the resistance value at point 0 and the resistance value at point d do not match and the difference is significant. . Therefore, regarding the resistance value, move the 0 point and d point laterally to the rlB characteristic,
Point f and point g, and the humidity H4 corresponding to point f and point g,
H, is determined, and the humidity difference d dH=H4-H is output as the amount of deterioration. Then, this d d H is displayed on the humidity deterioration amount display section 11.

(F) Effects of the Invention According to this invention, the humidity detection element is activated by a signal of a first frequency for measuring humidity and a signal of a second frequency higher than the first frequency for detecting deterioration. Since the capacitance change due to deterioration of the humidity detection element is detected by the output of the humidity detection element during each drive, there is no need to use a special humidity generation tank, calibration instrument, etc. If deterioration occurs, it can be detected immediately and the humidity detection element can be replaced at an appropriate time.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a humidity measuring device showing an embodiment of the present invention, and Fig. 2 shows deterioration caused by driving signals of the first and second frequencies to explain the deterioration detection operation of the humidity measuring device. Figure 3 shows the equivalent circuit of the humidity sensor. Figure 4 shows the relative humidity characteristics of the resistance and capacitance side components of the humidity sensor before and after deterioration due to tobacco. FIG. 1: Humidity detection element, 2: First frequency generator, 3: Second
frequency generator, 4: switching circuit, 5: temperature detection element, 6
: humidity calculation section, 7: first frequency characteristic storage section, 8: second frequency characteristic storage section, lO: humidity display section, 11: humidity deterioration amount display section.

Claims (1)

[Claims] (1) A humidity detection element, a first drive unit that drives the humidity detection element at a first frequency, and a second drive unit that drives the humidity detection element at a second frequency higher than the first frequency. , a switching unit that switches between the first drive unit and the second drive unit and connects it to the humidity detection element, and measures humidity based on the output of the humidity detection element when driven by the first drive unit. and means for detecting the amount of deterioration of the humidity detecting element based on the output of the humidity detecting element during each drive by the first drive section and the second drive section.