JPS6342423A - Water level sensor - Google Patents

Abstract

PURPOSE:To obtain a sensor which is fast in the response speed of water level detection by detecting a change in heat radiation state due to the contacting of water with a heat-sensitive resistance element as variation in oscillation period. CONSTITUTION:A bridge circuit 5 is constituted including the temperature sensing resistance element 1 as a component and its output is compared by a comparator 3 and fed back by a feedback circuit 6. Then, a voltage applied to the circuit 5 is varied so as to vary a current flowing to the element 1, and the variation in the output period of the comparator 3 is detected. At this time, the self-heating and cooling of the element 1 are repeated and the output of the comparator 3 turns on and off repeatedly. Then when water contacts the element 1, the heat radiation state changes and the output of the comparator 3 varies in period. The variation is detected by a detector 8 to improve the response.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a water level sensor using a temperature-sensitive resistance element used in washing machines and the like.

BACKGROUND OF THE INVENTION As shown in Fig. 3, a conventional water level sensor using a temperature-sensitive resistance element heats a thermistor 1 by itself, and then compares the voltage at that time with a reference voltage 2 obtained by dividing the resistance using a comparator. 3 for comparison, when water touches the thermistor IK,
As the heat is stolen, the temperature of thermistor 1 decreases and the resistance value increases, so the voltage of thermistor 1 becomes higher than the reference voltage 2, the output of the comparator 3 becomes "L", and the buzzer 4 etc. sounds. It has become.

Problems to be Solved by the Invention However, in such a configuration, when considering changes in the ambient temperature, the temperature at which the self-heating state is stable will change, so the reference voltage must be set in consideration of this change. As a result, the reference voltage is not high, and it takes time for the output of the comparator 3 to be inverted, resulting in poor responsiveness.

The present invention solves the above problems and provides a water level sensor with good responsiveness.

Means for Solving the Problems In order to solve the above problems, the present invention configures a bridge circuit including one temperature-sensitive resistance element, compares its outputs with a comparator, and compares the outputs with a feedback circuit. In order to feed back and change the current flowing through the temperature-sensitive resistance element, the voltage applied to the bridge circuit is changed, and a change in the output cycle of the comparator is detected by a detector.

Operation According to the present invention, the output of the comparator is repeatedly turned on and off by repeating self-heating and cooling of the temperature-sensitive resistor element. When water comes into contact with the temperature-sensitive resistance element, the heat dissipation state changes and the period of the output of the comparator changes. Since the change is detected by a detector, responsiveness is improved.

Embodiment FIG. 1 is a circuit diagram showing an embodiment of the water level sensor of the present invention. In Fig. 1, 1 is a temperature-sensitive resistance element (hereinafter referred to as a thermistor), and 6 is a resistance bridge circuit of which thermistor 1 is a part, and its large output (reference voltage) and output B (
thermistor voltage) is input to the comparator 3. 6 is a feedback circuit; when the output of the comparator 3 is "H", the transistor 7 is off; when the output is "L", the transistor 7 is on.

Further, the output of the comparator 3 is connected to a detector 8, and the detector 8 is composed of a counter 9 and a change detector 10. The output of the detector 8 is connected to the buzzer 4.

11 is a resistance.

Next, the operation will be explained. First, consider a state in which power is supplied and the thermistor 1 is not in contact with water. At this time,
Since the resistance value of the thermistor 1 is large, the outputs A and B of the bridge circuit 5 are B (thermistor voltage) rather than A (base voltage).
is higher, so the output of the comparator 3 becomes "L". Then, the transistor 7 of the feedback circuit 6 is turned on, and the power supply voltage is applied to the bridge circuit 6. Incidentally, changes in the input voltage and output voltage of the comparator 3 are shown in FIG. 2. At this time, since the voltage applied to the bridge circuit 5 is high, a large current is applied to the thermistor 1, causing self-heating. Then, the resistance value of the thermistor 1 decreases, and the thermistor voltage B decreases. When the reference voltage input is reached, the output of the comparator 3 becomes "H" and the transistor 7 is turned off. Then, current flows through the bridge circuit 5 via the resistor 11, so the applied voltage decreases, and both the reference voltage input and thermistor voltage B decrease. At this time, thermistor 1
Voltage B causes an undershoot, and then there is no self-heating, and as it is cooled, it rises and reaches the reference voltage input. Then, the output of comparator 3 becomes "L" again, so
Transistor 7 is turned on, and the voltage applied to bridge circuit 6 becomes high. Then, reference voltage input, thermistor voltage B
After that, the thermistor voltage B overshoots, but self-heating occurs again, and the thermistor voltage B
decreases. By repeating this operation, the output of the comparator 3 alternates between "H" and "L" at a constant cycle.

In the detector 8, a counter 9 measures the "H" (or 1L) time of the comparator 3, and the value is stored in the change detector 10.

Next, when water supply starts and water touches thermistor 1,
Since the heat dissipation state of the thermistor 1 changes, the comparator 30
On/off cycle changes. Then, since the measured value at the counter 9 changes, the change detector 1o can detect the change by comparing it with the previously stored value and drive the buzzer 4. Incidentally, the point C in FIG. 2 shows a state in which the thermistor 1 is in contact with water.

As described in detail, according to the present invention, changes in the state of heat dissipation caused by water touching the temperature-sensitive resistive element are recognized as changes in the oscillation period, so that the response speed of water level detection is fast and practical. This is what a water level sensor can provide.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the water level sensor of the present invention, FIG. 2 is an input/output waveform diagram of a comparator, and FIG. 3 is a circuit diagram showing a conventional example. 1... Temperature sensitive resistance element (thermistor), 3...
...Comparator, 5...Bridge circuit, 6...
...Feedback circuit, 8...Detector. Name of agent: Patent attorney Toshio Nakao and one other person, Figure 1 1-7-, 'bifu-himura each 4--7'su- 5--7 "Ril Koko 6, C- --74-Top Dimensions 7F Route 7-"-Transistor '22 Diagram Time

Claims (1)

[Claims] A bridge circuit that includes a temperature-sensitive resistance element as a part, a comparator that compares the output of the bridge circuit, a feedback circuit that changes the voltage applied to the bridge circuit according to the output of the comparator, and the comparator. A water level sensor consisting of a detector that detects changes in the output cycle of the water level sensor.