JPH02262044A - Atmosphere detector - Google Patents

Abstract

PURPOSE:To decrease errors caused by hysteresis by using a plurality of reference calibration curves in a region where hysteresis occurs in a moisture sensitive characteristic, and employing a capacitance/relative humidity converting method in consideration of the hysteresis. CONSTITUTION:In a region where hysteresis occurs in the moisture sensitive characteristic of a moisture sensitive element, a converting means performs the following capacitance/relative humidity conversion. Namely, the maximum value RHmax and the minimum value RHmin of the relative humidity closest to a measuring time before the time and the times tmax and tmin when the values are obtained are stored. Then, capacitance is measured at the time (t), and the measured value is made to be COBS. When the maximum value RHmax is less than a relative humidity RHo when hysteresis occurs in the used moisture sensitive element, the measured value COBS itself is used, and the relative humidity RH is computed. When RHmax exceeds RHo and tmax>=tmin, RH is computed by using a function f' which is obtained by correcting a function f1 in correspondence with the value of RHmax. Meanwhile, when tmax<tmin, the relative humidity is computed by using a function f0' which is obtained by correcting a function f0 in correspondence with the value of RHmin.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to an atmosphere detection device using a capacitive humidity sensing element having a polymer thin film as a humidity sensing element, and more specifically, to The present invention relates to a method of converting the capacitance of a humidity element to relative humidity.

(Prior Art) As a method of detecting humidity in an atmosphere, a method that utilizes changes in the electrical characteristics of a moisture-sensitive material is well known.

Examples of materials whose properties change due to adsorption and desorption of moisture include metal oxide ceramics, electrolytes such as lithium chloride, hygroscopic organic polymers and polymer electrolytes, and polymer composite materials containing conductive fillers. is known, and many types have already been put into practical use.

The detection principle of moisture-sensitive elements using these moisture-sensitive materials is to detect changes in the electrical conductivity and dielectric constant of the moisture-sensitive material caused by adsorption and desorption of moisture into the moisture-sensitive material, using a sensor between electrodes formed in an appropriate shape. It is detected as a change in impedance, electrical resistance, or capacitance.

Among the moisture-sensitive materials mentioned above, capacitance-variable moisture-sensing elements using hygroscopic polymer thin films have a wide moisture-sensing range and fast response speed, and their structure is relatively simple, making them easy to manufacture. Because it is easy, it is easy to mass produce and has low cost.

Cellulose derivatives, polyvinyl alcohol-based resins, polyamide-based resins, polyimide-based resins, acrylic-based resins, polyester-based resins, etc. are known as polymeric moisture-sensitive film materials used in such moisture-sensitive elements. A commonly used device configuration is a three-layer parallel plate capacitor structure in which the upper and lower surfaces of a polymer moisture-sensitive film are sandwiched between electrodes.

An atmosphere detection device using such a capacitive humidity sensing element includes a humidity sensing element, means for detecting the capacitance of the humidity sensing element,
It is generally comprised of a conversion means for converting the capacitance into relative humidity, and means for outputting the relative humidity value by some method. Among these, in the conversion means for converting capacitance to relative humidity, a calibration curve showing the relationship between the capacitance of the humidity sensitive element and relative humidity is obtained in advance, and the conversion is performed using the relational expression (approximate expression). At this time, if the humidity sensing element has temperature characteristics, temperature correction is applied to the relational expression, and if a single relational expression cannot convert a wide range of relative humidity with sufficient accuracy, multiple relative humidity values are applied. Generally, the relative humidity is divided into ranges and converted using the relational expression most suitable for each range, and efforts have been made to improve the accuracy of the output relative humidity value.

(Problems to be Solved by the Invention) As mentioned above, humidity sensing elements using thin polymer films have great expectations for practical use due to their characteristics. A phenomenon (hysteresis) is observed in which the detected capacitance value differs depending on whether it is a dehumidification process or a dehumidification process. That is, the capacitance value at a certain relative humidity may differ depending on the history of the humidity sensing element up to the time of measurement.

In this way, when there is hysteresis in the humidity characteristics, when converting capacity to relative humidity using a calibration curve determined in advance as described above, it is important to check whether the calibration curve is based on the humidification process or the dehumidification process. An error corresponding to the magnitude of the hysteresis will occur depending on whether the reference value is used as a reference, or the average value of both of them is used as a reference. That is,
In a conversion method in which there is a one-to-one correspondence between capacitance and relative humidity, even if the humidity sensing element itself and the capacitance detection accuracy are high, the influence of hysteresis on the overall accuracy of the relative humidity detection device cannot be ignored.

Of course, efforts have been made to reduce the hysteresis of the moisture-sensitive element itself by changing the material of the polymer thin film and the element structure.
Moisture sensing elements currently on the market have a relative humidity of 2~2.
At present, it is unavoidable that hysteresis occurs from 3% RH to 7 to 8% RH. Furthermore, this hysteresis is the 5th type that requires the most precision for controlling air conditioning equipment.
This is often noticeable around 0 to 70% RH, and improvement has been desired.

Therefore, the present invention solves the problem of the method of converting capacitance into relative humidity when the humidity sensing element has hysteresis in an atmosphere detection device using a capacitive humidity sensing element as described above, and improves accuracy. The purpose of the present invention is to provide a high-quality atmosphere detection device.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides a capacitive humidity sensing element whose capacitance changes depending on the relative humidity to be detected, and A calibration curve is used to convert the capacitance of the capacitive humidity sensing element into relative humidity, and in a region where hysteresis occurs in the humidity sensitive characteristics, a plurality of reference calibration curves are used to convert the capacitance of the capacitive humidity sensing element into relative humidity. The gist is to have the means.

Further, in the present invention, when the local maximum value of the relative humidity nearest before the detection time is larger than the relative humidity at which hysteresis occurs in the humidity sensitivity characteristic, the conversion means converts the minimum value and maximum value of the relative humidity closest before the detection time. The gist also includes that a calibration curve is obtained by correcting the standard calibration curve from the context of the two extreme values, and that the capacitance of the capacitive humidity sensing element is converted into relative humidity using this corrected calibration curve.

(Function) In explaining the function, first, a region in which hysteresis occurs in the humidity-sensing characteristics of the capacitive humidity-sensing element will be described with reference to the drawings.

FIGS. 1 and 2 are diagrams showing basic configuration examples of a capacitance-variable humidity sensing element, and FIGS. 1(a) and 2(a) are plan views, and FIG. 1(b) is a plan view. and FIG. 2(b) are the first
FIG. 2 is a sectional view taken along the line X--X of FIG. 2(a) and FIG. 2(a).

In each figure, 1 is an insulating substrate, on which a lower electrode 2 is formed. A moisture sensitive film 3 made of a thin polymer film is formed on the lower electrode 2. Furthermore, a moisture-permeable upper electrode 4 is formed on the moisture-sensitive membrane 3.
Lead wires 5 are attached to the upper and lower electrodes 2.4, respectively, to detect capacitance. Figures 1 and 2
In the figure, each layer is formed on an insulating substrate 1, but a structure in which a pair of electrodes are formed directly on both sides of a polymer film (self-supporting film) (
(not shown) is also generally known.

Known materials used for the polymer moisture sensitive membrane 3 include cellulose derivatives, polyimide resins, and the like. FIG. 3 shows an example of the humidity characteristics of a moisture-sensitive element (the structure is the same as in FIG. 2) using a polyimide resin synthesized mainly from tetracarboxylic dianhydride and aromatic diamine as a moisture-sensitive film. The humidity-sensitive characteristics shown in the same figure are obtained by gradually humidifying the humidity-sensitive characteristics from 10% RH until reaching a certain relative humidity, and then conversely humidifying the humidity at 10% RH.
A humidity cycle is set in which the humidity is gradually dehumidified up to H, and the capacitance change of the humidity sensing element during this cycle is shown.

As can be seen from Figure 3, no hysteresis is observed in humidity cycles when the relative humidity is below 50% RH, but considerable hysteresis is observed when the upper limit (maximum value) of the humidity cycle is above 70% RH. . In this 7111 constant, when the humidity cycle is repeated, and when the humidity cycle is started from the upper limit value, similar results can be obtained with good reproducibility. That is, when the relative humidity increases, as shown in Figure 3, it changes along the lower curve (where the capacitance value is relatively small) of the two characteristic curves, and the relative humidity increases. When the value decreases, it changes on the upper curve. Additionally, humidity cycle measurements can be made over a relatively short period of time (
There is almost no change in the characteristic curve shown in Figure 3 whether the test is carried out at a rate of change of about 3% RH/1 minute) or for a long time (10% RH/1 hour). .

A similar phenomenon occurs in the case of cellulose derivatives, for example, when using ethyl cellulose or ethyl hydroxyethyl cellulose, the upper limit of the humidity cycle is 4.
Hysteresis becomes noticeable at 0 to 60% RH.

The cause of this hysteresis is not necessarily clear, but the phenomenon of adsorption and desorption of water molecules to the polymer thin film is not only due to simple physical adsorption, but also due to interactions between the adsorbed water molecules.
This is thought to be due to the inclusion of an adsorption/desorption mechanism with large activation energy that involves the higher-order structure of the polymer chain.

The above-mentioned phenomenon is common to capacitive humidity sensing elements that are generally widely used. The relationship is shown in Figure 4.

In contrast, in the atmosphere detection device of the present invention, when converting the measured capacity into relative humidity using the relational expression of the calibration curve, if the relative humidity has a history larger than a specific value,
That is, when there is hysteresis, it is possible to convert it into relative humidity using a different calibration curve that takes into account the magnitude of hysteresis, thereby further increasing the accuracy of the output relative humidity value.

In addition, in the capacitance/relative humidity conversion of the present invention, as data: ■ two standard calibration curves for the humidification process and dehumidification process; The time, , is required, and from the above ■, it is possible to determine whether the direction of change at the time of detection is in the humidifying direction or the dehumidifying direction, based on the history of the humidity sensing element, that is, the relationship between the maximum value and the minimum value. It is possible to determine whether conversion taking hysteresis into consideration is necessary from the nearest local maximum value, and to obtain a more accurate relative humidity value.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 5 to 8.

In the atmosphere detection device of this embodiment, the conversion means performs the following capacitance-relative humidity conversion operation in a region where hysteresis occurs in the humidity-sensing characteristics of the humidity-sensing element. This will be explained using the flowchart shown in FIG.

First, the relationship between capacity and relative humidity in the humidification process and dehumidification process is determined and used as two reference calibration curves.

That is, at a certain temperature, using a branch type humidity generator etc. that has sufficient accuracy as a primary standard of relative humidity,
Measure the humidity characteristics of the humidity sensing element. At this time, the characteristics of the humidification process are as follows: After conditioning the humidity sensing element by leaving it at the lowest possible relative humidity (for example, 5% RH) for a long time, the relative humidity is gradually increased, and the function fO
seek.

Also, regarding the characteristics of the dehumidification process, after conditioning the device by leaving it in a high humidity range where no dew condensation occurs, the relative humidity is gradually lowered and fl is determined in the same way. These humidity characteristics have some temperature characteristics, so we performed the same a-1 constant for several temperatures and took the correction coefficient into account to calculate f.
o and fI are determined as functions of capacitance C and temperature T (step 11). Hereinafter, it is assumed that fo to f+ includes a temperature correction term in total.

FIG. 6 shows an example of the reference calibration curves for the humidification process and dehumidification process obtained as described above.

In the converting means of this embodiment, the nearest relative humidity local maximum value RHMAX and local minimum value RHMIN before the measurement time, and the time tMA×, t when these values were obtained, are
After storing the MIN (step 12), conversion is performed according to the following procedure.

The capacity is measured at time t, and the measured value is set as CoB5 (step 13). Then tMAxS tMIN
Regardless of the value of , when the maximum value RHMAX is less than the relative humidity RHo at which hysteresis occurs in the humidity sensing element used (approximately 50% RH in the case of polyimide in Figure 4), there is no need to consider hysteresis. , fo calculates the relative humidity RH using the capacitance measurement value CQBS as it is (
Yes in step 14, step 15).

If RHMAX exceeds RHO, tMAX and tM
tM
When Ax≧tMrN, it is determined that the humidity change at a certain point in time is in the dehumidification process (Yes in step 16),
Function f+ that corrects function J'l according to the value of RHMAX
' Calculate the relative humidity (step 17.18)
. On the other hand, when tMAX<tMIN, it is determined that the humidity change at the time of measurement is in the humidification process.
o) Calculate the relative humidity using the function fo corrected according to the value of RHMIN (step 19.2
0).

Details of the execution in step 17 and step 18 are shown in FIGS. 7 and 8, respectively.

First, in FIG. 7, the larger RHMAx is, the larger the hysteresis is, and the actual dehumidification characteristic curve f1 is f
The curve is close to l, and conversely, the smaller RHMAX is (R
Hl, 4AX > RHO range) fI (in the figure, f
1') approaches fO. In other words, it is possible to draw a newly corrected characteristic curve f' with RHMAX as the starting point within a range with fI as the upper limit and fo as the lower limit. For example, depending on the magnitude of the value of RHMAX, the curves f1 and fO can be internally divided. f like do
Find l. However, when RHMAX>95%RH,
Even if the value of RHMAX changes somewhat, fl is given as almost the same relationship, so it is treated as fI' - fI.

Further, FIG. 8 shows an example of correction of the function fO in the humidification process, and in exactly the same way as in FIG.
Obtain and calculate o'. Note that if RHMIN<10%RH, it can be treated as fo'-fo.

Furthermore, the relative humidity output R determined as above
H (step 21) is the conventional extreme value RHMAX, RH
Compared to M I N, it is updated as appropriate with time t.

By the way, although the above-mentioned correction method takes into account the history of the humidity-sensitive element, -temporal extreme values do not affect subsequent humidity characteristics. In other words, when the relative humidity rises or falls rapidly, changes in the order of a few seconds to tens of seconds do not leave a history, but only when exposed to almost the same humidity for a few minutes. become. Therefore, when updating RHk4A× and RHMIN, it is necessary to make decisions on a time scale of several minutes or more.

Specific Example The relative humidity of the same atmosphere was measured using an atmosphere detection device A equipped with the conversion means of this example and an atmosphere detection device B as a comparative example, which was not equipped with the atmosphere detection device A. Both of the atmosphere detection devices A1B have the same configuration and use moisture sensing elements having almost the same moisture sensing characteristics, and a calibration curve is obtained for each humidity sensing element. Note that the atmosphere detection device B performs conversion to relative humidity using a calibration curve of the humidification process.

The magnitude of hysteresis (maximum value) in a humidity cycle where the lower limit of the humidity sensing element is 10% RH and the upper limit is 90% RH is 5.
．． 5%RH, relative humidity at which hysteresis occurs is 50%R
It is H. The temperature of the atmosphere was 25° C., and the humidity was changed as appropriate using a commercially available split-flow type precision humidity generator (Model 5RH-1 manufactured by Shinyei Corporation). The outputs (stable values) of detection devices A and B when the humidity setting value is changed stepwise at 15 minute intervals are shown in the ninth column.
Shown in the table of figures. As is clear from the table, the atmosphere detection device equipped with the conversion means of this example can perform measurements with higher accuracy than the comparative example.

[Effects of the Invention] As explained above, according to the present invention, in a region where hysteresis occurs in the humidity-sensitive characteristics of a humidity-sensitive element, a plurality of reference calibration curves are used and a capacitance-relative humidity conversion method that takes hysteresis into account is adopted. This makes it possible to reduce errors caused by hysteresis and perform highly accurate relative humidity measurements.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a capacitive humidity sensing element applied to the atmosphere detection device according to the present invention, FIG. 2 is a diagram showing another example of the configuration of the capacitive humidity sensing element, and FIG. Figure 1 or 2
Characteristic diagram showing the humidity characteristics of the capacitive humidity sensing element shown in Fig. 4.
The figure is a characteristic diagram showing the relationship between the upper limit of the measurement range of relative humidity by the capacitive humidity sensing element and the magnitude of hysteresis. Figure 5 is a flowchart, Figure 6 is a capacity and
A characteristic diagram showing an example of humidity characteristics that serve as a reference when converting relative temperature. Figure 7 is a diagram for explaining a method of correcting the characteristic curve based on hysteresis in the dehumidification process. Figure 8 is a diagram showing the characteristics based on hysteresis in the humidification process. A diagram for explaining the curve correction method, Figure 9 shows the relative humidity f according to a specific example.
It is a figure which shows il fixed value together with a comparative example. 2.4: Upper and lower electrodes; 3: Moisture-sensitive film that constitutes a capacitive humidity-sensitive element together with the upper and lower electrodes. Figure 1 (a) Figure 1 (b) Figure 2 (a) Figure 2 (b)

Claims (2)

[Claims] (1) A capacitive humidity sensing element whose capacitance changes depending on the relative humidity to be detected, and a calibration curve determined in advance to convert the capacitance of the capacitive humidity sensing element into relative humidity and to adjust the humidity sensitivity characteristics. 1. An atmosphere detection device comprising: converting means for converting the capacitance of the capacitive humidity sensing element into relative humidity using a plurality of reference calibration curves in a region where hysteresis occurs. (2) When the local maximum value of the relative humidity nearest before the detection time is larger than the relative humidity at which hysteresis occurs in the humidity sensitivity characteristic, the conversion means converts the minimum value, maximum value, and both extreme values of the relative humidity closest before the detection time. 2. The atmosphere detection device according to claim 1, wherein a calibration curve is obtained by correcting the standard calibration curve from the context of the above, and the capacitance of the capacitive humidity sensing element is converted into relative humidity using the corrected calibration curve. .