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Simple Hot Water Level Indicator Using NTC

2015-01-09 22:33  
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This circuit is a circuit diagram to show various levels of hot water in a tank. This circuit works when SW1 is a normally open press button switch which allows you to see the level of hot water in the hot water tank. When pressed the voltage difference at the junction of the thermistor and preset fixed voltage compared with the op-amp non-inverting input. Depending on the hot water in the tank, the thermistor resistance will activate the op-amp output to swing to almost full supply voltage and the corresponding LED light. Opamp circuit diagram using a version of the LM324 quad opamp quad but each can be used or even four single op-amp. R2-R5 I used 330ohm resistors, but the value is not critical. Lower value output LED light. NTC1-4 maximum thermistor resistance should be approximately the same fixed resistor and preset. As a negative temparature coefficient (NTC) thermistor is used, then their resistance decreases as temperature increased. NTC1-4 thermistors should spread evenly over the height of the tank. I put NTC1 about 4 inches from the top of my tank and the others spaced evenly at the height of the hot water tank. Hot water rises fully lowest water level sensor indicates the heat and should be about 8 to 10 inches from the bottom of the tank. The following is a schematic drawing:

Simple Hot Water Level Indicator Using NTC1 Simple Hot Water Level Indicator Using NTC

Alternative thermistor can be used with different ranges of resistance, but the presets P1 to P4 must also be changed as well. R7-10 series resistance, only needed if your thermistor resistance is several ohms at the hottest temperature. P1 – P4 Elected to match the resistance of the thermistor when cold. R1 & R6. This is the same resistor and biased op-amp inverting input supply voltage half. For full calibration of the hot water tank P1-4 to adjust so that all the LED lights on. As hot water rises, the sensor at the bottom of the tank will be a maximum level of hot water. “Hot” can be translated as 50c to 80C in the preset P1-4 allows adjustment of this range.

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