There are two main principles of liquid level sensor: one is to use sliding potentiometer as detection element. When the float moves, it drives the potentiometer to move, and the resistance value changes. It can be detected by an ohmmeter, so that the oil level can be determined. One of its disadvantages is that when oil dirt covers the potentiometer, its resistance will also change, which will introduce errors and lead to the decrease of sensor life. The other is to use the inductance coil as the detection element, and use the float to drive the inductance coil to change the frequency of the oscillation circuit, and then the value of the liquid level can be known by detecting its frequency. Its disadvantages are complex structure, troublesome debugging, high cost and high price, which limit its application scope. At present, many liquid level sensors are made of reed switches. Because of their long service life, safe and reliable action and no spark, they are widely used to detect the liquid level of oil tanks and generator sets.
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