JPS6133373B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a humidity detection circuit.

For example, in order to detect humidity for the purpose of humidity control, it is common to construct a detection circuit using a humidity detection element. Some of these humidity detection elements are accompanied by chemical effects when current is applied to them, so care must be taken when applying current. That is, when a relatively large direct current is passed through the humidity detection element, the possibility of erroneous detection increases due to chemical effects.

However, since the circuit to which the humidity detection element is combined uses a DC power supply, a DC current also flows through the humidity detection element. Therefore, the only countermeasure that has been taken in the past has been to increase the magnitude of the DC current.

An object of the present invention is to provide a humidity detection circuit that can effectively flow an alternating current to a humidity detection element.

To achieve this objective, in the present invention, one end of the humidity detection element is connected to the intermediate connection point of a resistive voltage divider circuit connected between both ends of the DC power supply, and a square wave voltage is applied which repeats the potential at each end of the DC power supply in a periodic alternating manner. By connecting the other end of the element to a circuit, the element is energized in two directions, forward and reverse, and a circuit is constructed that detects humidity from a change in potential at the intermediate connection point.

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

FIG. 1 shows an embodiment of the present invention.
is a power transformer, whose secondary output is formed into a DC constant voltage Vcc by a rectifying and smoothing circuit 2, and is connected to resistors 3 to 3.
Power is supplied to a resistor bridge circuit consisting of 6. On the other hand, a sine wave voltage taken out from a predetermined tap of the secondary winding of the power transformer 1 is passed through a waveform shaping circuit 7 to form a square wave voltage in which a DC constant voltage Vcc and a ground potential GND are periodically repeated alternately. A humidity detection element 8 is connected between the output end of the waveform shaping circuit 7 and an intermediate connection point of one of the two resistance voltage divider circuits in the resistance bridge circuit. Then, the intermediate connection points of the resistors 3, 4 and 5, 6 of the resistor bridge circuit are connected to the comparator 9.

Figure 2 a, b, and c show the voltage and current waveforms at each point in the circuit of Figure 1;
is the output voltage Va of the waveform shaping circuit 7, b is the midpoint voltage vb of one resistor voltage divider circuit in the resistor bridge circuit, and c is the current i of the humidity detection element 8.
A and iB are shown respectively. In other words, the output voltage va of the waveform shaping circuit 7 alternates between the DC power supply voltage Vcc and the ground potential GND, and the midpoint voltage vb of the resistor voltage divider circuit is around the intermediate value between the DC power supply voltage Vcc and the ground potential GND. Repeat high and low in a square wave pattern. At this time, the direction of the current flowing through the humidity detection element 8 changes alternately. The magnitude of the current iA in one direction and the current iB in the other direction is determined according to the resistance ratio of the resistors 3 and 4 of the resistor bridge circuit, and if both resistors 3 and 4 are equal, iA =
It becomes iB.

Figures 3a and 3b show the two inputs of the comparator 9, that is, the potentials V+ and V- at the intermediate connection points of the resistors 3, 4 and 5, 6 in the resistor bridge circuit, and the output VOUT of the comparator 9 in low humidity and high humidity. The figures are shown for each case of humidity. If the humidity is high,
If the input and output shown in FIG. That is, the midpoint voltage V+ of the resistors 3 and 4 is high or
Although a small change occurs, the midpoint voltage V- of the resistors 5 and 6 remains at a predetermined value. And V+ is V
- is exceeded, the output VOUT of the comparator 9 is generated. In the above embodiment, a square wave voltage is obtained by applying the AC power supply voltage to the waveform shaping circuit, but the configuration of the square wave voltage source is not limited to this.

In the present invention, as described above, the circuit is configured to apply sequential and reverse currents to the humidity detecting element periodically and alternately, so that the humidity detecting element does not produce any chemical action, and therefore humidity detection with less detection error is possible. The circuit can be provided.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
Figures a, b, and c show the voltages at various parts in the circuit of Figure 1,
FIGS. 3A and 3B are waveform diagrams showing the input and output voltages of a comparator to show the humidity sensing operation in the circuit of FIG. 1. 1...power transformer, 2...rectifier smoothing circuit, 3-6
...Resistor, 7. Waveform shaping circuit, 8. Humidity detection element,
9... Comparator.

Claims (1)

[Claims] 1. A resistive voltage divider circuit connected between both ends of the DC power supply to form a voltage intermediate between the potentials at each end of the DC power supply, and a square wave voltage forming circuit that repeatedly forms the potential at each end of the DC power supply in a periodic alternating manner; A humidity detection element is provided, one end of which is connected to an intermediate voltage point of the resistive voltage divider circuit, and the other end of which is connected to an output point of the square wave voltage forming circuit, and the humidity detecting element is configured to detect a voltage change at the intermediate voltage point of the resistive voltage divider circuit. A humidity detection circuit that detects humidity by