JPS60186916A - Control circuit for humidity sensor - Google Patents

Abstract

PURPOSE:To obtain an inexpensive sensor circuit having a long lifetime by providing an analog switch in series to a humidity sensor to control the voltage impressed to the sensor. CONSTITUTION:The AC voltage of a sine wave, etc. is impressed to a humidity sensor 3 from an oscillation circuit 2 via a resistance 4. Then the humidity detection voltage is obtained at a juncture 20 and then supplied to a comparator 8 to be compared with the voltage value of a variable resistor 10 for set humidity. Thus a signal of H or L level is obtained and supplied to a controller 12 to control the working of an air conditioner, etc. An analog switch 13 is provided in series to the sensor 3 and turned on in a humidity measurement mode and off in a non-measurement mode respectively by the controller 12. Thus the lifetime of the humidity sensor circuit 3 can be increased since the output voltage of the circuit 2 is impressed to the circuit 3 since the switch 13 is turned on only in a measurement mode.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit for a humidity sensor in an air conditioner or the like.

A conventional circuit of this type is shown in FIG. In the figure, (11 is a DC power supply, (2) is an oscillation circuit such as a sine wave AC, (3) is a humidity sensor, and (4) is a resistor.

The output of the oscillator circuit (2) is applied to the humidity sensor (3) via a resistor (4). (5) is a buffer circuit, (6)
is a diode, and (7) is a capacitor, and the diode (6) and capacitor (7) constitute a rectifier circuit. (8
) is a comparator, (9) is a resistor, 01 is a variable resistor for humidity setting, Qll is a pull-up resistor for the comparator (8), α is a control device for an air conditioner, etc., ■, 00
, (2) is a connection point.

Next, the operation will be explained. Figure 2 shows the humidity sensor (3
) with the relative humidity on the horizontal axis,
If the resistance value is plotted on a logarithmic scale on the vertical axis, the characteristic curve will be a straight line sloping downward to the right. When an AC voltage such as a sine wave is applied to the humidity sensor (3) through the resistor (4), the resistance value of the humidity sensor (3) and the resistor (4) are connected to the connection point ■.
) and a voltage determined by the output voltage value of the oscillation circuit (2) is generated. Generally, the humidity sensor (3) has a high resistance value of several hundred ohms, so this divided AC voltage is rectified by a diode (6) and a capacitor (7) via a buffer circuit (5). This rectified DC normal pressure value is compared with the voltage value determined by the resistor (9) and the variable resistor axis for setting humidity by the comparator (8), and the output is input to the control device 02 at H level and L level. be done. A control device operator controls the operation of an air conditioner or the like (not shown) based on the output signal of the comparator (8).

Here, the lifespan and reliability of the humidity sensor (3) are determined by contamination of the humidity sensing part by dust etc. adhering to its surface and polarization of the humidity sensing part by voltage application. Usually, contamination of the humidity sensing part is dealt with by installing a heater around the humidity sensor (3) and using heat to incinerate the dust, or cleaning it by washing with water. However, since the polarization of the humidity sensor (3) inside the element is determined by the energization time itself, sufficient measures have not been taken in the past, and the lifespan and reliability of the humidity sensor (3) are generally limited. It is significantly inferior to that of electronic components.

Conventional humidity sensor control circuits are configured as described above, and since AC voltage is always applied to the humidity sensor, the lifespan of the humidity sensor circuit is determined by the humidity sensor itself, which makes it short and reliable. Deterioration of sex was a major drawback.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional devices, and it is a humidity sensor control circuit that applies AC voltage to the humidity sensor only when measuring humidity, greatly increasing the lifespan and reliability. is intended to provide.

An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 3, fl) is a DC power supply, (2) is an oscillation circuit such as a sine wave AC, (3) is a humidity sensor, (4) is a resistor,
(5) is a buffer circuit, (6) is a diode, (7) is a capacitor, and the input terminal of the buffer circuit (5) is a resistor (4).
) and the humidity sensor (3), and the output terminal of the buffer circuit (5) is connected to the capacitor (7) via the diode (6). (8) is a comparator, (9) is a resistor, and fil is a variable resistor for setting humidity. The inverting input terminal of the comparator (8) is the resistor (9)
and the connection point QB between the variable resistor OI and the non-inverting side input terminal is connected to the connection point @ between the diode (6) and the capacitor (7). 0υ is a pull-up resistor, α is a control device for the air conditioner such as a microcomputer guard, and the output terminal of the comparator (8) is connected to the pull-up resistor αυ and is also input to the control device (12.03 is An analog switch connected in parallel to the humidity sensor (3).
When measuring humidity, it is turned on by the controller α and the oscillation circuit (2
) is applied to the humidity sensor (3), turned off when humidity is not being measured, and the oscillation circuit (2) is applied to the humidity sensor (3).
It is possible to prevent the output voltage from being applied.

In general households, the humidity is reduced to 1% using an air conditioner.
It takes an average of several tens of seconds to change the RH, so the control device az
The humidity detection sampling period of 1 minute is sufficient, whereas the response speed of the humidity sensor (3) is within a few seconds, so as a result, the analog switch al must be turned on for about 3 seconds every 1 minute. necessary and sufficient. Therefore, by configuring the above configuration, the humidity sensor (
Voltage is applied to 3) only when analog switch a3 is ON, so even if the humidity sensor (3) itself has a short lifespan, the lifespan of the humidity sensor circuit is approximately 20% longer than that of a conventional humidity sensor circuit. It can be made twice as long.

Furthermore, although the above embodiment describes the case of an analog switch, a relay or other switching device may also be used, and according to the present invention, a relay or other switching device may be used. An analog switch is installed in the sensor, and the voltage application to the humidity sensor is controlled by the analog switch 0N10FF, so the device can be made at low cost.
It also has the advantage of providing a humidity sensor circuit with a long life.

[Brief explanation of drawings]

FIG. 1 is a conventional humidity sensor control circuit diagram, FIG. 2 is a humidity sensor characteristic diagram, and FIG. 3 is a humidity sensor control circuit diagram according to an embodiment of the present invention. (2)...Oscillation circuit, (3)...Humidity sensor, (
4)...Resistance. (5)...buffer circuit, (6)...diode,
(7) Capacitor, az... Control device for air conditioners, etc. (13... Analog switch. In the diagram, the same reference numerals indicate the same or equivalent parts. Agent: Masuo Oiwa

Claims (1)

[Claims] 0) A control circuit for a humidity sensor, characterized in that it includes a switching element in series with the humidity sensor. (2) The humidity sensor control circuit according to claim 1, characterized in that an analog switch is provided in series with the humidity sensor, and the analog switch is opened and closed in synchronization with the humidity detection sampling period.