Resistance Level Detectors detects level changes by the change in resistance of a partially submerged electrical element.
Construction of Resistance Level Detectors
The electrical sensing element consist of a precision-wound helix resistor that has about 28 contacts per foot.An outer jacket of flexible protective material also acts as a pressure receiving diaphragm.
Principle of Operation - Resistance Level Detector
The pressure of the liquid in the tank acts upon the jacket-diaphragm and causes the resistance element to contact the steel base trip. Below the surface of the liquid,the resistor is shorted. The resistor remains unshorted above the surface,and it is this portion that is metered to provide the level reading. Two wires from the sensor top transmit an electrical resistance signal that is related to the distance from the tank top to the surface of the liquid. Typically 1 ohm is equal to 1 cm.
Advantages of Resistance of Level detector
The sensor strip remains fixed in position,has no moving parts and provides a continuous indication of resistance.
The wingdings these sensors are purely resistive, they cannot store or release electrical energy.Thus resistance sensors qualify as intrinsically safe devices and can be used with explosive liquids and dust.