Working principle: 1. It operates by generating an ultrasonic wave or pulse and measuring a time it takes for the echo to return. 2. There are two way of measurement of liquid level: Doppler Type Time difference type 3. The ultrasonic waves generated by transmitter and directed towards the liquid surface in the tank which is to be measure. 4. These waves get reflected from the surface of the liquid and are received by the receiver. 5. The time take by the wave is a measure of the distance travelled by the wave. Therefore the time‘t’ between transmitting and receiving a wave is proportional to the distance ‘d’ between ultrasonic set and surface of the liquid in the tank. 6. As the distance ‘H’ between ultrasonic set and the bottom of the tank is fixed time ‘t’ is measure of level ‘l’
Advantages: 1. Non-contact type level measurement technique. 2. There is no moving parts. 3. The output is unaffected by changes in composition, density, electrical conductivity of process fluid.
Disadvantages: 1) Temperature compensation is essential. 2) Accuracy may get affected by the dirt, contamination, solid suspensions in process fluids. 3) Ultrasonic Transmitter is subject to many interferences so as strength of the signal may dilute. 4) Ultrasonic level measurement devices do not work satisfactorily in areas involving vacuum or high pressure conditions
Application: 1. It is used in a nuclear power factory to ensure enough water to be turned into steam. 2. It can be used to control the flow rate by means of detecting level of process fluid in tank. 3. It is used to measure level of tank of height more than 50 feet.