Novel Liquid Level Sensor

Novel Liquid-Level Sensor Circuit diagram. Normally, the level of a liquid in a container is determined by sensing changes in the capacitance or resistance between a pair of electrodes that are immersed in the liquid. Generally speaking, this technique requires fairly complicated schemary to protect the electrodes against electrolysis (and associated corrosion). In addition, in many cases the liquid must be conductive for the measurement principle to actually be usable. The schema presented here shows that an alternative approach is possible.

Novel Liquid-Level Sensor Circuit diagram:

Novel Liquid-Level Sensor Circuit Diagram

Here we utilise the fact that a PTC resistor warms up in pro-portion to the amount of current flowing through it, with the result that its resistance increases. If a PTC resistor is immersed in a liquid, the additional warmth is dissipated in the liquid and the resistance remains nearly constant.

 If the level of the liquid drops below the immersion depth of the resistor, the change in the resistance can be easily sensed by a subsequent comparator stage. The PTC resistor should be isolated from the fluid into which it is immersed, in order to prevent undesirable electrolytic processes from taking place. A further improvement in the characteristics of the schema can be achieved by using a logic schema such as a micro controller to apply power to the schema only at predefined times and then switch off the power after sampling the comparator output.