JPH0151771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for minimizing undesirable characteristics of electrical humidity sensors that operate based on changes in impedance, particularly capacitive humidity sensors in which the moisture sensitive material is formed from an organic polymer. .

Several humidity sensors are known with an electrical detection system in which the change in impedance is proportional to the humidity to be measured. This type of humidity sensor is described, for example, in US Pat. No. 3,168,829;
They are described in US Pat. No. 3,350,941 and Finnish Patent No. 48,229, respectively.

In the capacitive humidity sensor described in Finnish Patent No. 48229, the dielectric material consists of a polymer film, the dielectric coefficient of which is a function of the amount of water absorbed into the polymer film. With these humidity sensors and other humidity sensors based on changes in impedance, an undesirable phenomenon exists, especially when measuring high humidity. This phenomenon is, for example, a slow creep of the sensor resulting from various factors. In this case, the problem is generally a reversible phenomenon.

Therefore, the purpose of the present invention is to improve the suppression of the above-mentioned phenomenon by increasing the responsiveness of the sensor, and to improve the measurement accuracy, especially when measuring high relative humidity, for example, exceeding 90%. It's about letting people know.

To achieve the above object, the main feature of the invention is that the humidity sensitive material of the humidity sensor is heated to a higher temperature than the ambient temperature, at least when the relative humidity is high.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which illustrate a capacitive humidity sensor using an organic polymer and a moisture-sensitive material.

The humidity sensor shown in FIGS. 1 and 2 is itself described in Finnish patent application no. 48229. Humidity sensor 10 is supported on a substrate 11 made of an inert material such as glass. On the substrate 11 there is a metal-plated bottom contact 12 made by methods known in thin-film technology, on which a connecting conductor 21 is brazed in the terminal section indicated by the reference numeral 16. be done. The capacitance is then detected, measured and displayed by the devices shown in FIG. 1 as blocks 20 and 22.

The active or moisture sensitive material of the humidity sensor 10 is a thin polymer film 13 on the order of 10 μm thick.
A thin water vapor permeable surface contact 14 is deposited on this polymer film 13 by vacuum deposition or sputtering, or is chemically created, without making any electrical contact with the bottom contact 12. The measured capacitance C _M is d and e (Fig. 2)
Bottom contact 12 and surface contact 14 in the area of
It is formed by connecting two capacitors in series.

When water molecules are absorbed into the moisture sensitive material comprising the polymer film 13, water retention occurs through two distinct phenomena. One fixation occurs at the molecular level and produces a rapid and nearly linear response as the capacitance C _M changes. Another phenomenon is the so-called swelling effect that occurs in extremely humid conditions (generally above 90% relative humidity), whereby water becomes trapped within the pocket-like cavities of the moisture-sensitive material made of the polymeric film 13. It will be done. This phenomenon is much slower than the previous one and causes sensor creep during high humidity measurements. Another result is the Q value (power factor) of the sensor capacitance
This is actively exploited in embodiments of the present invention in order to reduce the effects of the aforementioned undesirable phenomena, as described below.

As shown in FIG. 1, the humidity sensor 10 is supplied with a measuring current e of a suitable frequency, which current forms the basis of the humidity measured by the humidity sensor 10. For the reasons mentioned above, especially at high humidity levels, the impedance Z _M measured at the terminal section 16
Since is not a pure capacitance but has a certain resistance component, the capacitance to be measured is expressed as _M =R ₀ +1/jωC (that is, resistance and capacitance connected in series). Here, R ₀ is the loss resistance component of the polymer thin film 13 as a dielectric, and C _M is the capacitance component of the measured impedance. At high humidity levels, the swelling effect mentioned above becomes a loss resisting component.
Increase R _O. Therefore, the loss effect W that occurs in the loss resistance component R _O and heats the humidity sensor 10
is equal to I ² R _O (W=I ² R _O ). Here, I is the rated measurement current (root mean square current).

According to this invention, the heating of the humidity sensor 10 is performed by
The harmful moisture absorbed by the humidity sensor 10 is rapidly released from the moisture-sensitive material as the temperature rises, and the humidity sensor 10, which is slightly warmer than the surrounding air, warms the surrounding air and increases the relative humidity of the air at the boundary surface. It is considered to have the function of preventing the humidity from rising to a harmful level from the operating point of the humidity sensor 10, or to have either of these functions.

As shown in FIG. 1, an insulating layer (moisture sensitive material) formed of a polymer thin film 13 of a humidity sensor 10
is the current I applied directly to the humidity sensor 10 itself.
heated by. This current I is the same as the measuring current of the sensor itself and causes losses in the dielectric (moisture sensitive material) of the capacitance being measured. As shown in FIG. 1, heating of the moisture sensitive material described above is accomplished in practice by increasing the input voltage U of the humidity sensor 10 to an appropriate level. An advantage of this embodiment of the invention is that humidity sensor 10 is self-regulating. In other words, this self-regulating system means that it heats up significantly when the humidity is high (resulting in a relatively high loss resistance R _O ), and heats it less at low humidity levels where no heating is required (resulting in a relatively high loss resistance R _{O )} .
(becomes lower). Therefore, heating according to the invention does not result in significant errors or the need for correction in humidity measurements.

In the embodiment shown in FIG. 1, the temperature T _S of the dielectric (moisture sensitive material) is measured by a temperature sensor 15 arranged in connection with the insulating layer (moisture sensitive material), and the measurement result is transmitted to the conductor 18. It is taken out through the wafer and used as appropriate for heating the insulating layer (moisture-sensitive material). In practice, the measurement result by said temperature sensor 15 is a function of the temperature T _S (which is selected according to experience).
As a result, temperature control is performed by adjusting the input voltage U.

As shown in FIG. 1, the ambient temperature T _O is also measured by the temperature sensor 17, and the measurement result is sent via the conductor 19 to the measuring device 20 for adjusting the heating of the humidity sensor 10 as appropriate. used in methods. In FIG. 1, block 22 represents a relative humidity (RH) indicator.

As mentioned above, according to the method of the invention, the humidity information provided by the humidity sensor 10 itself can be used to adjust the heating energy. In addition, the information obtained as the temperature T _S of the dielectric (humidity sensitive material) and the ambient temperature T _O can also be used to calculate the temperature difference ΔT = T _S − when the relative humidity is high, for example over 90%.
It can be used to adjust the temperature to compensate with a signal proportional to T _O.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a part of an apparatus for carrying out the method of the present invention, and FIG. 2 is a sectional view taken along the line -- of the actual temperature sensor shown in FIG. 10... Humidity sensor, 11... Board, 12...
Bottom contact body, 13... Polymer thin film, 14... Surface contact body, 15... Temperature sensor, 16... Terminal part,
17...Temperature sensor, 18...Conductor, 19...Conductor, 20...Measuring device, 21...Connecting conductor, 22
...Relative humidity indicator.

[Claims]

1. An oxide semiconductor sensor that changes resistance depending on the air-fuel ratio, a cathode layer on one side of a plate or cylinder made of an oxygen ion conductor, and an anode layer on the other side facing this, and a porous cathode layer. A sensor (hereinafter referred to as a sensor) that detects the air-fuel ratio by applying a positive voltage to the anode layer and a negative voltage to the cathode layer, and detecting the air-fuel ratio by applying a positive voltage to the anode layer and a negative voltage to the cathode layer.
a sensor section consisting of a limiting current type oxygen sensor); a resistance measuring section that measures the resistance of the oxide semiconductor over a wide range; and a resistance measurement section that determines whether there is an excess of fuel or an insufficient amount of fuel compared to the stoichiometric air-fuel ratio from the resistance of the oxide semiconductor. a limiting current detection section that applies a voltage to the limiting current type oxygen sensor and detects the limiting current only in the case of fuel shortage; and selecting the air-fuel ratio determined from the oxide semiconductor sensor if there is excess fuel. an air-fuel ratio detection device comprising: a selection unit that selects an air-fuel ratio obtained from a limiting current type oxygen sensor if there is a fuel shortage; 2 The air-fuel ratio output determined based on the oxide semiconductor sensor is a normal value in the excess fuel region.