JPS61296250A - Method for correcting output of humidity sensor - Google Patents

Abstract

PURPOSE:To obtain accurate output, by a method wherein relative humidity is divided into plural sections and temp. correction function is set at every section and the output of the humidity sensor in a measuring atmosphere is corrected on the basis of the characteristic curve based on output voltage at relative humidity between two points set by fixed point humidity method after a predetermined period was elapsed and the error function obtained from a preset standard characteristic curve. CONSTITUTION:Temp. correction function obtained by dividing relative humidity at every predetermined % is set. After a predetermined period was elapsed, two points are set by a fixed point humidity method and the output of a temp. sensor 24 receives temp. correction on the basis of temp. correction function. A characteristic curve is calculated at two corrected points by a method of least squares to be stored in ROM21 from an input terminal 20. Error function is calculated from this characteristic curve and the standard characteristic curve preliminarily stored in ROM21 by CPU25 to be stored in ROM23. Subsequently, a humidity sensor 22 is exposed to a measuring atmosphere and the obtained output is corrected on the basis of the error function read from RAM23 to obtain accurate output.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention is a sensor output correction method for correcting changes in the output characteristics of a humidity sensor due to temperature, element variations, changes over time of the element, etc. It is about the method.

"Conventional technology" Conventionally, in order to compensate for changes in the characteristics of the output of a humidity sensor due to temperature, a thermistor was incorporated into a humidity detection circuit that mainly uses a humidity sensor, and changes in outside air temperature were detected by the thermistor, and the output characteristics were adjusted. A method was taken to correct this.

Further, Japanese Patent Publication No. 5B-21458 is known as a method for correcting temporal changes in a humidity sensor to obtain correct measured values, and the details are as follows.

(1) First measurement method - In Figure 5, the temperature of the constant temperature oven (1) is measured at the input terminal (
2) Adjust the temperature to a predetermined temperature higher than the dew point of the sample gas supplied from step 2).

■The dry gas itself D supplied from the input terminal (3) and the saturated humid gas W passed through the saturated tank (4) containing water are supplied to the mixing tank (5), and the dividing ratio of D and W is supplied to the mixing tank (5). A gas W+D of known humidity is supplied to the test chamber (7) through the first tube (6) with various settings.

Read the scale of the humidity sensor (8) at the temperature set in ``■■'', determine the relationship between the scale and humidity at the predetermined temperature, and create a correction curve.

■ Close the valve device (9) and open the second pipe (11).
) to input the sample gas from the input terminal (2) into the test tank (7
).

(2) Determine the humidity of the sample gas from the scale of the humidity sensor (8) at this time and the correction curve (2), and obtain an output from the output terminal (2).

(2) Second measurement method ■Same as the first ■.

■Same as the first ■.

■Read the indicated value of the humidity sensor (8) at a predetermined temperature. ■Switch the valve devices ll (9) and (10), and
6) to supply the wet gas W+D to the test chamber (7),
υJ so that the indicated values at There has been a problem in that errors caused by variations in temperature characteristics of the elements cannot be eliminated. Furthermore, the method of correcting changes over time in a constant temperature bath has the problem that the apparatus is large-scale and extremely expensive. In other words, not only is bulky equipment such as a thermostat, saturation tank, mixing tank, and test tank required, but also in order to obtain a calibration curve,
There was a problem in that the controls such as temperature control of the constant temperature bath, setting control of various division ratios of W and D, switching control of the valve device, and control of exchange of gas in the test chamber were extremely complicated.

The present invention has been made to solve the above-mentioned problems, and includes means for presetting standard characteristic lines of relative humidity and output voltage, and Means for dividing into a plurality of points and setting a temperature correction function for each section; Means for setting at least two points by a fixed point humidity method after a predetermined period of time and correcting with a temperature correction function; means for measuring the output voltage at relative humidity and determining a characteristic line based on the least squares method; means for determining an error function from the new characteristic line and the standard characteristic line; exposing the humidity sensor to the measurement atmosphere; This method includes means for obtaining an output at that time and correcting it using the error function to obtain a correct output.

r action” First, a function fr for correcting temperature characteristics is stored.

This function is both a function of temperature and a function of relative humidity, so the term for relative humidity is a predetermined percentage.
The functions are stored for each division. Furthermore, standard characteristic lines are stored in advance. After a predetermined period of time has elapsed, at least two points set by the fixed point humidity method are subjected to temperature correction using a temperature characteristic correction function. A characteristic line is determined using the least square method using these two corrected points, and an error function is determined from this new characteristic line and the standard characteristic line. Here, the humidity sensor is exposed to the measurement atmosphere, an output at that time is obtained, and this is corrected by the error function to obtain a correct output.

"Example" Hereinafter, one embodiment of the present invention will be described based on the drawings.

First, a case will be described in which a change due to temperature is corrected.

Since a variable resistance humidity sensor has a negative humidity coefficient at the same relative humidity, its output voltage characteristic is such that as the temperature rises, the output voltage also increases as shown in FIG. Further, the function fa for correcting the temperature characteristics is a function of temperature as well as a function of relative humidity. This is because the temperature coefficient of the humidity sensor element differs depending on the relative humidity. More specifically, in FIG. 1, if the characteristic at 25° C. is taken as the standard, the correction values for the characteristics at other temperatures change as the relative humidity changes and are not uniform with respect to this standard characteristic. For example, if the correction value of 90% RH at 45°C <X),
50% R11 correction value (y) at 5℃ and 20% at 45℃
The correction values (z) of R11 are all different. The same applies to other relative humidities. Therefore, the function fT for correcting the temperature characteristics is f7=f7(F,...h)...(1)
becomes.

However, it is difficult and complicated to express the relative humidity term in equation (1) mathematically, so it is necessary to
According to each division, f = fT (t
, ) ... (2) and expressed as a function of temperature. Specifically, each characteristic line is determined and the input terminal (2o) in FIG.
1) must be entered in advance.

Next, the output voltage is determined by the humidity sensor (22), and this is fH, and the relative humidity is h.

fs ” fN(h) ...(4), which is a function only of relative humidity. Therefore, the output voltage f after temperature correction is f=fH(h) +fr(t) ...(5) In this way, by measuring temperature and humidity separately, the temperature of the humidity sensor can be corrected.

Next, the characteristics of the humidity sensor (22) are determined from the standard characteristic line,
A correction method in the case of variations due to changes over time or variations in elements will be explained.

In Figure 2, (fst) is the standard characteristic line, (fH2)
Let be the characteristic line after fluctuation. The atmosphere of the humidity sensor (22) is set to relative humidity using a humidity standard device using saturated salt.

and set it to l+2. These two points are set at one point between 20 and 30%, which is particularly important as relative humidity, and one between 70 and 80%. Then, the output voltages corresponding to these two points are measured and are designated as fH2(h1) and fH2(hz). Assuming that this term does not include the term corrected by temperature, the output after temperature correction using equation (5) is calculated by multiplying the temperature at the time of measurement by 1. If t is 2, then this(,
In equation 6), fT(l2,) and fy(shi2) are (
3) It can be determined by the formula.

Next, FIG. 3 shows a temperature-corrected characteristic line. In this Fig. 3, the standard characteristic line L+(h) is
(21).

Next, a straight characteristic line f2(h) is drawn from the two points of the outputs f2(hx, shi) and fz(hz, shi,), which also include the temperature correction term after the characteristic change obtained using equation (6). demand. This f2(
The difference Δf (h) between the standard characteristic line fs (h) and the standard characteristic line fs (h) is determined.

Δf(h)=f! (ht) f2 (h) ...(
7) This Δf(h) is stored in RAM (23).

Next, the humidity sensor (22) is placed in the measurement atmosphere, and the output fn2 (h+s) at that time is measured. at the same time,
If the temperature of the measurement atmosphere is measured by the temperature sensor (24) and this is I, then f 2 (hm, 7 m) = fH2 (ha) +
fy(t, m) .=(8), and the temperature is corrected by this equation (8). Furthermore, by adding the term Δf(h) obtained from equation (7) to equation (8), we get

f(hm,L,s)"f)12(hm)+1'7(Lm
)+Δf(ha+)...(9) is the output corrected for temperature correction and temporal change (device characteristic variation). The output f after this correction is exactly the standard characteristic f1 shown in FIG.

The flow of the above amendment is as follows.

■Storing equation (3) in ROM (21).

(2) Store the standard characteristic f in FIG. 3 in the ROM (21).

(2) Set two relative humidities, h, and h2, using a humidity standard device.

- The CPU (25) calculates equation (6). That is, each output fl (h t
), fHL(h2) is given by fr(sh1) according to equation (3).
) and f7(j2) are added to perform temperature correction.

■ f2 (ht, t+), f2 (h2
, t, 2), a new characteristic line f2(h) is obtained.

■Determine Δf01) using equation (7), and further obtain this Δf(
h) is stored in RAM (23).

■Exposing the humidity sensor (22) to the measurement atmosphere.

- The CPU (25) calculates equation (9). That is, the output fj+2(hm) has f7(tm) and Δf(hm
) to obtain the final output f (hm, t, m).

"Effects of the Invention" Since the present invention employs the above-described method, correction using simple calculations can cause errors in the temperature characteristics of the humidity sensor due to changes in relative humidity or variations in the temperature characteristics of the elements. can be prevented. Further, by determining the temperature coefficient of the circuit board in advance in addition to temperature compensation of the humidity sensor, a special circuit is not required for temperature compensation of the board. Furthermore, as long as the standard characteristic line is stored in memory, there is no need to measure the initial characteristic line for each element constituting the sensor, and therefore there is no need to make adjustments due to differences in the characteristics of the elements.

[Brief explanation of drawings]

1, 2, and 3 are characteristic diagrams for explaining the correction method according to the present invention, FIG. 4 is a block diagram of a microcomputer that calculates the correction method according to the present invention, and FIG. 5 is a conventional correction method. FIG. (20)...Standard characteristics input terminal, (21)...RO
M, (22)...humidity sensor, (23)...RAM
, (24)...Temperature sensor, (25)...CPU.

Claims (4)

[Claims] (1) Means for setting standard characteristic lines of relative humidity and output voltage in advance, means for dividing relative humidity into multiple sections and setting a temperature correction function for each section, and means for setting fixed point humidity after a predetermined period of time. A means for setting at least two points using the method and correcting it using a temperature correction function, a means for measuring the output voltage at the relative humidity of these two points and determining a characteristic line based on this using the least squares method, and this new method. means for determining an error function from the characteristic line and the standard characteristic line; and means for exposing the humidity sensor to the measurement atmosphere, obtaining the output at that time, and correcting this using the error function to obtain the correct output. Features a humidity sensor output correction method. (2) The humidity sensor output correction method according to claim 1, wherein the relative humidity divisions are equal intervals between 10 and 20%. (3) The humidity sensor is of a variable resistance type, and the actual measured value is adjusted by a temperature and aging correction function to match the standard characteristics at 25°C, as described in claim 1 or 2. How to correct the humidity sensor output. (4) A method for correcting a humidity sensor output according to claim 1, wherein the calculation is performed by a microcomputer.