Quiery about Ultrasonic level & flow Transmitter

The sensor sends out ultrasonic impulses towards the surface of the liquid. The impulses rebound of the surface back to the sensor. Based upon the time and frequency of the return signal, the level of the liquid can be computed.

Basically, ultrasonic flow meters sense the flow through the pipe wall without coming into contact with the medium.

Ultrasonic level sensors are mounted at the top of the tank, away from the medium being measured. You bore a hole at the top and mount your sensor there. So, technically, the sensor may still come into contact with the medium if the tank overflows. Also, if your medium produces fumes, these will contact the sensor also. You may, however, order the chemical resistant type from the supplier/manufacturer.

http://en.wikipedia.org/wiki/Ultrasonic_flow_meter

http://en.wikipedia.org/wiki/Level_sensor#Ultrasonic_Level_Sensors