JPH0155481B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a humidity detection device provided in, for example, an air conditioner.

(Prior Art) Generally, due to its characteristics, if a voltage is continuously applied to a humidity sensor in one direction, a polarization effect will occur and the humidity sensor will be destroyed. Furthermore, since the humidity sensor includes a capacitance in addition to a resistance, there is a problem in that it is difficult to directly obtain DC voltage data.

For this reason, AC driving using a sine wave has conventionally been used as a driving method for humidity sensors. For example, as shown in FIG. 1, an AC power source 1 and a drive circuit 2 are used to drive the humidity sensor 3 with AC. Then, the AC humidity data obtained from the humidity sensor 3 is converted into DC data by a rectifier circuit 4 and an integrating circuit 5 to obtain humidity information and use it for humidity control.

(Problem to be Solved by the Invention) However, in the conventional circuit as described above, in addition to the operating power supply (DC) for each circuit, an AC power supply 1 for driving the sensor is required, and an integrating circuit for DC conversion is required. 5 etc., making the configuration complicated.

Furthermore, since the number of circuit stages for converting the output data (alternating current) of the sensor 3 into direct current data is large, there is a drawback that there is a large variation in the direct current data output due to conversion errors.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a humidity detection device that can obtain highly accurate DC data with a simple circuit configuration while ensuring the safety of the humidity sensor.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the humidity detection device of the present invention includes a humidity sensor, a circuit for applying a rectangular wave alternating current signal to the humidity sensor, and an output of the humidity sensor. and a circuit that reads the humidity information as humidity information at a timing delayed by a certain period of time from the change point of the rectangular wave alternating current signal applied to the humidity sensor.

(Function) In the humidity detection device of the present invention, since the humidity sensor is driven by a rectangular wave alternating current signal, it will not be destroyed by polarization.

In addition, the rectangular wave AC signal can be easily obtained using a normal DC power supply, which simplifies the circuit configuration.
Furthermore, since the output of the humidity sensor is read as humidity information at a certain time delay from the change point of the rectangular wave AC signal applied to the humidity sensor, high accuracy is achieved without being affected by the capacitance contained in the humidity sensor. DC data can be obtained.

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

In Figure 2, 11 is a decimal counter,
Counts reference clock input and generates BCD code output. 12 is a decoder, and counter 11
It decodes the outputs of and generates "1" outputs sequentially at the "0" to "9" output terminals. 13 is a binary counter, and “1” is output from the “9” output terminal of the decoder 12.
The output is inverted for each input. Reference numeral 14 denotes a humidity sensor drive circuit, in which, for example, C-MOS type inverters 15 and 16 are connected in series, and the inverter 1 in the subsequent stage
One end of the humidity sensor 17 is connected to the output end of 6,
The other end of this sensor 17 is connected via a resistor 18 to the output end of the inverter 15 at the previous stage.

Then, the output of the binary counter 13 is led to the input terminal of the preceding stage interface 15, and the sensor 17 and the resistor 1
The connection end of 8 is led to the hold output end of the sample and hold circuit 19. 20 is an AND gate, which performs AND processing on the output of the binary counter 13 and the output of the decoder 12, for example, the "8" output terminal.
21 is a monostable multi-circuit, and the AND gate 2
A pulse output of 0 is derived, and at its rising edge, a pulse with a constant width is output and supplied to the sample hold circuit 19 as a sampling pulse.

The operation of the humidity detection device having the above configuration will now be described with reference to FIG. Decimal counter 11
counts the reference clock input, and the count output is decoded by the decoder 12. For each “1” output from the “9” output terminal of the decoder 12, the binary counter 13
The output of the binary counter 13 and the output of the "8" output terminal of the decoder 12 are AND-processed by the AND gate 20. This and gate 2
A sampling pulse of a constant width is generated from the monostable monomulti circuit 21 in synchronization with the rise of the zero pulse output. In this case, the sampling pulse and the output pulse of the binary counter 13 have a certain time delay determined by the output timing relationship between the output terminal "8" and the output terminal "9" of the decoder 12.

On the other hand, the output pulse of the binary counter 13 is guided to the sensor drive circuit 14.
In this case, a rectangular wave AC voltage is applied to the humidity sensor 17.

That is, when the output of the binary counter 13 is at the "L" level, the output terminal of the inverter 15 is at a high potential and the output terminal of the inverter 16 is at a low potential.
A current flows through the humidity sensor 17 from the output end of the inverter 15 to the output end of the inverter 16 .
On the other hand, when the output of the binary counter 13 is at the "H" level, the output terminal of the inverter 15 has a low potential and the output terminal of the inverter 16 has a high potential. A current flows in the direction of the output end, and a rectangular wave alternating current signal is applied to the humidity sensor 17.

The output voltage of the sensor drive circuit 14 is determined by the sample hold circuit 19 using a sample pulse delayed by a certain period of time from the change point (rising edge) of the drive waveform of the sensor drive circuit 14 (output pulse of the binary counter 13). sampled. The hold output (DC data) of this sample hold circuit 19 is read as humidity data.

In the above embodiment, the sensor output is held as an analog signal, but the sensor output may be directly A/D (analog/digital) converted, stored, and updated to obtain digitized humidity data. That is, in FIG. 4, a timing circuit 41 generates a drive pulse and a data strobe pulse having a constant phase timing therewith. The drive pulse is guided to a humidity sensor drive circuit 14, and the output voltage of this circuit 14 is guided to an A/D converter 42 where it is A/D converted. This converter 4
The digital output of No. 2 is led to the register 43, where it is stored and updated at a timing delayed by a certain period of time from the change point of the drive pulse by the data strobe pulse, and stable digitized humidity data is obtained. The relationship between these operation timings is shown in FIG.

According to the configuration shown in FIG. 4 described above, since digitized data is read instead of analog data, characteristics against noise etc. are good, and by using a digital circuit, it can be realized at low cost.

[Effects of the Invention] According to the present invention, since the humidity sensor is driven by a rectangular wave alternating current signal, the alternating current power supply that was conventionally required is not required, and the circuit configuration is simplified.

Furthermore, since the sensor output is read at a timing delayed by a certain period of time from the point of change of the rectangular wave alternating current signal, even if the humidity sensor contains a capacitance, its influence can be reduced and humidity detection accuracy can be increased.

Furthermore, since the sensor output is DC, there is no need to convert AC output to DC data, and variations in humidity data due to conversion errors are eliminated.

[Brief explanation of drawings]

Fig. 1 is a circuit block diagram showing a conventional humidity detecting device, Fig. 2 is a circuit diagram showing an embodiment of the humidity detecting device according to the present invention, and Fig. 3 is shown to explain the operation of Fig. 2. 4 is a circuit diagram showing another embodiment of the present invention, and FIG. 5 is a waveform diagram shown to explain the operation of FIG. 4. 11... Decimal counter, 12... Decoder, 13...
Binary counter, 14...Humidity sensor drive circuit, 17
...Humidity sensor, 19...Sample hold circuit, 2
0...AND gate, 21...monostable multi-circuit.

Claims (1)

[Claims] 1. A humidity sensor, a circuit that applies a rectangular wave alternating current signal to the humidity sensor, and a circuit that reads the output of the humidity sensor as humidity information at a timing delayed by a certain period of time from a change point of the rectangular wave alternating signal. A humidity detection device characterized by: