JPS62113055A - Moisture measuring apparatus - Google Patents

Abstract

PURPOSE:To always enable a highly accurate measurement of moisture regardless of the length in the lead, by canceling inherent stray capacitance possessed by the lead by signal outputted from a capacitance canceling circuit. CONSTITUTION:A moisture measuring apparatus body 10 is made up of three circuits, a moisture detecting electric circuit 11, a stray capacitance canceling circuit 12 and an adder 13. The stray capacitance canceling circuit 12 outputs dummy capacity -C2 and -C3 to cancel the capacitance C2 between l1-l2 and the capacitance of l1 via earth stray capacitance C3 and adds the signals to the adder 13. The outputting of the dummy from the stray capacitance canceling circuit 12 makes the moisture detection capacitance C and the capacitance C1 inferent to the moisture sensor coincide completely thereby avoiding the effect of the leads on the stray capacitance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for measuring humidity, and in particular, to lengthening the lead wire between a sensor serving as a detection part and the main body of the device without reducing measurement accuracy. The present invention relates to a humidity measuring device capable of measuring humidity.

[Conventional technology]

In response to the increasing sophistication of various control devices, the physical quantities that serve as the basis for their control are also required to be more accurate, and of course humidity, which is one of those physical quantities, is also required to be more accurate. However, accurate measurements are required. Particularly in response to the computerization of devices, it is necessary to convert measured quantities into electrical quantities, and a humidity measuring device that satisfies such requirements is required. However, when detecting humidity, it is necessary to place the sensor part of the device in the atmosphere where the measurement must be performed, and since moisture and dirt may adhere to it and it is affected by heat, a sensor that can always measure with high precision is required. There are many difficulties in configuring.

For this reason, despite the desire to develop highly accurate equipment in the field of humidity measurement, the reality is that there are more technical issues to be solved than in the field of measuring physical quantities such as temperature and weight. . Under the above circumstances, a capacitive humidity sensor using a thin polymer film has been provided and is attracting attention.

The operating principle of this humidity sensor is as follows. That is, when a polymer such as cellulose acetate is used as a moisture-sensitive material, the dipole moment of the water molecules adsorbed on this polymer increases the dielectric constant of the polymer, so the polymer with such characteristics can be used as a moisture-sensitive material. It is possible to form a capacitor using this as a dielectric. Therefore, its operating principle is that by measuring the change in capacitance of this capacitor, the relative humidity around the polymer can be measured. Furthermore, Figure 4 shows the relationship between the capacitance of a humidity sensor and humidity, and the change in capacitance with respect to relative humidity shows good linearity, indicating that this type of sensor has high measurement accuracy in principle. I understand.

FIGS. 2 and 3 show the structure of a capacitive humidity sensor using a thin polymer film, which is a sensor constructed based on the above principle. FIG. 2(A) is a plan view of the sensor, and FIG. 2(B) is a side view. Glass base 1 (for example, about 0.
A planar comb-shaped lower electrode 2 is formed by depositing gold to a thickness of 2 tm. Note that the film thickness of this lower electrode 2 is 0.1 to 1 μm. 11 and 12 are lead wires connected to each of these two lower electrodes. Next, a thin polymer film layer 3 which is a moisture-sensitive material is placed to cover the lower electrode 2.
form. The polymer thin film layer 3 is formed by immersing the substrate in a solution prepared by dissolving a moisture-sensitive material such as acetate cellulose in a solvent such as alcohol or ethylene dichloride, and then pulling it up. As a result, an amorphous polymer thin film layer 3 is formed to cover the lower electrode 2. In this case, if the polymer thin film is made too thin, the upper electrode, which will be described later, will be short-circuited, whereas if it is too thick, the response will be reduced. Reference numeral 4 denotes an upper electrode, which is formed by vapor depositing gold on the upper surface of the polymer thin film layer 3.

FIG. 3 shows an electrical equivalent circuit of the humidity sensor described above.

As is clear from this figure, the humidity sensor has capacitors C1 and 02 connected in series between lower electrodes 2a and 2b.

[Problem that the invention seeks to solve]

Although the capacitive humidity sensor using a thin polymer film described above has high measurement accuracy, the lead wire cannot be made long for the following reasons, and the range of use of the device is limited. Ta. Particularly when the object to be measured is in a high-humidity atmosphere, short lead wires are a serious disadvantage since placing the main body of the measuring device containing a complicated electrical circuit in this atmosphere may cause failure.

5 and 6 show the circuit configuration of a conventional device. In the figure, Ill and IL2 are lead wires connecting the humidity sensor 6 and the humidity detection electric circuit 7, C is a humidity detection capacitor, and C1 is a capacitance of the humidity sensor. FIG. 6 shows the capacitance of the entire detection circuit in this configuration. In addition, the above-mentioned code C
, C, and other symbols in FIG. 6 have the following meanings.

C2:j! Capacitance between 1 and β2 C3: Stray capacitance between n1 and ground C4: j! Stray capacitance E between z and ground: Earth ground point Here, stray capacitance means the electrical capacity that the lead wire itself has.

In the above configuration, the humidity detection capacity C of the device can be expressed by the following formula.

As is clear from the above equation (1), the capacitance C of the humidity sensor is influenced by C2 and stray capacitances C3 and C4. Since this stray capacitance changes depending on the length of the lead wire, the longer 11.12 is, the greater its influence becomes. Therefore, in the conventional configuration, short lead wires had to be used in order not to reduce measurement accuracy.

[Means for solving problems]

The present invention has been constructed in view of the above-mentioned problems, and one of the two lead wires is connected to the humidity detection electric circuit, and the other lead wire is connected to the humidity detection electric circuit. The circuit is bypassed and connected to the output side of this humidity detection electric circuit, and furthermore, a stray capacitance cancellation circuit is provided separately from the humidity detection electric circuit, and this stray capacitance cancellation circuit and the humidity detection electric circuit are connected to each other. This device is characterized in that it is configured such that each of the two is connected to an adder.

[Effect]

As described above, the present invention provides a circuit for canceling stray capacitance separately from the electric circuit for detecting humidity, and cancels the capacitance specific to the lead wire by the canceling capacitance output from the circuit for canceling stray capacitance in the adder. This allows highly accurate humidity measurements to be made without being affected by stray capacitance.

〔Example〕

Embodiments of the present invention will be specifically described below based on the drawings.

In FIG. 1, the same reference numerals used to describe the conventional device represent the same parts. That is, 6 is a humidity sensor, 11.12 is a lead wire connected to each of a pair of lower electrodes provided on this humidity sensor 6, C is a humidity detection capacitor, and C is a humidity sensor.
, is the capacitance of the humidity sensor 6, C2 is the capacitance between β1 and β2,
C3 indicates ff, the stray capacitance between the ground and E, and E indicates the grounding point.

Next, reference numeral 10 indicates the main body of the humidity measuring device, which includes an electric circuit 11 for detecting humidity, and a circuit 1 for canceling stray capacitance.
It consists of three circuits: 2 and an adder 13. Of these, the quality detection electric circuit 11 is connected to one of the two lead wires (vAII!). l and its output end is connected to the adder 13.

Similarly, the circuit 12 for canceling stray capacitance is also connected to the adder 13.
Further, one of the output ends of the adder 13 is connected to another lead wire 12 that bypasses the humidity measuring device main body 10.

Of this configuration, the stray capacitance canceling circuit 12 is A! ,
dummy capacitance CZ, C3 to cancel the capacitance of stray capacitance C3 between -782 and C2 and n, and ground.
is output, and these signals are added in an adder 13. Therefore, the humidity detection capacitance C can be expressed by the following equation.

c= C(C,+C2)+C31] −(C2+C3)
-C1... (1) In other words, as is clear from Part 2 (1), by outputting a dummy output from the stray capacitance cancellation circuit 12, the humidity detection capacitance C and the capacitance C1, which is a capacitance specific to the humidity sensor, are completely This makes it possible to avoid the influence of stray capacitance of the lead wires. Therefore, there is no problem even if the lead wire is extended.

〔Effect of the invention〕

As described above, the present invention comprises three circuits: a humidity detection electric circuit, a stray capacitance canceling circuit, and an adder, and uses a signal output from the stray capacitance canceling circuit to detect the inherent characteristics of the lead wire. This cancels stray capacitance, making it possible to constantly measure humidity with high precision regardless of the length of the lead wire.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a humidity measuring device showing an embodiment of the present invention;
Figure 2 (A) is a top view of the humidity sensor, and Figure 2 (B) is the same (A).
), FIG. 3 is an electrical equivalent circuit diagram of the sensor shown in FIG. 2, and FIG. 4 is a diagram showing the relationship between capacitance and humidity in the humidity measurement sensor shown in FIG. Figure 5, 6th
The figure is a circuit diagram of a conventional humidity measuring device. 6... Humidity sensor 10... Humidity measuring device body
11... Electric circuit for humidity detection 12... Circuit for canceling stray capacitance 13... Adder C... Humidity detection capacitor CI...
・Humidity sensor capacity

Claims (2)

[Claims] (1) A humidity measuring sensor made of a moisture-sensitive material made of a polymer whose dielectric constant increases due to the hyperbolic moment of adsorbed water molecules, and a humidity measuring device body into which signals from this sensor are input. In a device configured to be connected by a lead wire, three circuits are configured in the humidity measuring device body: an electric circuit for humidity detection, a circuit for canceling stray capacitance, and an adder. The humidity detection electric circuit is connected to one of the two lead wires and is also connected to the adder, and the signal output from the stray capacitance canceling circuit detects the inherent stray A humidity measuring device characterized in that it is configured to cancel out the capacitance and make the capacitance of the humidity sensor equal to the detection capacitance of the humidity measuring device itself. (2) Among the two lead wires, the stray capacitance between the lead wire l_1 connected to the humidity detection electric circuit and the ground is C_3, and the lead wire l_2 which is not connected to the humidity detection electric circuit If the stray capacitance between
The humidity measuring device according to claim 1, characterized in that it is configured to output -C_2.