JPS5848614Y2 - humidity detection circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improvement of a humidity sensor, and is capable of applying a constant AC voltage to a ceramic humidity sensor using a DC power supply with a simple circuit configuration.

Conventionally, when measuring humidity sensors made of ceramic elements, continuous application of DC voltage causes a polarization effect. This has been done with the addition of exchanges.

The former has the disadvantage that measurements cannot be repeated frequently, and the latter has the disadvantage that the circuit configuration is complicated to obtain a constant voltage.

The present invention easily obtains alternating current from a direct current power source by using a transistor as a switch without using a transformer.The embodiments shown in the drawings will be described below.

In the figure, 1 is an AC power source, which may be a commercial power source, and is connected in series to an inverter 2.3.

The outputs of inverters 2 and 3 are applied to the respective bases of transistors 6 and 7 via resistors 4 and 5, respectively.

The collectors of the transistors 6.7 are connected to one end of the DC power supply 10 via resistors 8 or 9 each having a constant resistance value, and the emitters of each transistor 6.7 are connected to the other end of the DC power supply 10.

A humidity sensor 11 made of a ceramic element or the like is connected between both collectors of the transistor 6.7.

One end (2) of the humidity sensor 11 also serves as a non-inverting input of the operational amplifier 12 as an input of the rectifier circuit.

The operational amplifier 12 and a diode 13 form a known rectifier circuit, and the rectified output is smoothed by a capacitor 14.

Resistor 15 is a load resistance. The smoothed output becomes the input of the comparator 16, and the DC voltage is input to the resistor 17 and 1.
It is compared with the reference voltage divided by 8.

In this operation, the transistors 6 and 7 are alternately turned on in accordance with the cycle of the AC power supply 1.

Therefore, the current flowing from the resistor 8 to the transistor 7 and the current flowing from the resistor 9 to the transistor 6 alternately pass through the humidity sensor 11 in opposite directions.

Ignoring the conduction resistance of the transistor, the potential at one end (■) of the humidity sensor 11 is as follows when the transistor 7 is conductive:
It becomes the partial pressure value of the resistor 8 and the humidity sensor 11, and becomes 0 potential when the transistor 6 is conductive.

As a result, by rectifying and smoothing the voltage at the 0 point, a DC voltage that matches the resistance value of the humidity sensor 11, or in other words, the humidity change, is obtained at the load resistor 15.

For example, if the humidity sensor changes depending on the humidity in the range of 100 kg to 500 kg, then resistor 8 is set to 300 kg.
If kQ is used, the divided voltage value of the terminal (2) can be obtained as a voltage varying from 1/4 to 5/8 of the voltage of the DC power supply 10.

As described above, the present invention makes it possible to obtain a simple humidity detection circuit in which AC is applied to the humidity sensor by only considering the accuracy of the stabilized DC power supply 10 and the resistor 8.

[Brief explanation of the drawing]

The drawing is a circuit diagram of an embodiment of a humidity detection circuit according to the present invention. 1... AC power supply, 6, 7... Transistor, 8, 9... Resistor, 10... DC power supply, 11... Humidity sensor.

Claims (1)

[Scope of utility model registration request] A humidity sensor is connected between the collectors of two transistors whose bases are alternately driven at a constant cycle and whose emitters are grounded, each with a resistor as the collector load, and the output is taken out from one end of the humidity sensor. circuit.