In this method, an ultrasonic transmitter receiver is mounted on top of the tank for measurement of level. The ultrasonic beam generated by transmitter is projected downwards towards the liquid surface in the tank which is to be measured. This beam is reflected from the surface of the liquid and is received by the receiver. The time taken by the beam is a measure of the distance travelled by the beam. Therefore the time ‘t’ between transmitting and receiving a pressure pulse is proportional to the distance ‘h’ between ultrasonic set and surface of the liquid in the tank.