This type of level transmitter includes a sensor wire, connected to a piezoceramic sensor inside the transmitter. This sensor wire runs straight down the sensor tube and is attached to the tension fixture at the bottom of the sensor tube.Sensor tube passes through a hole in a float. This float consists of circular magnets and moves up and down the sensor tube while floating on the liquid surface.
To find the elevation of the float and thus the level of liquid, the transmitter sends a short current pulse down the sensor wire. This pulse sets up a temporary magnetic field along its entire length. A timing circuit is triggered ON at the same time.
This magnetic field created pulse of electric current interacts with the magnetic field of permanent magnets inside the float and a torsional force is generated in the wire much like ultrasonic vibration or wave and travels back to the piezoceramic sensor at a particular speed. When the sensor detects the torsional wave, it produces an electrical signal that notifies the timing circuit that the wave has arrived and stops the timing circuit. The timing circuit measures the time interval (TOF) between the start of the current pulse and the wave’s arrival. From this information, the float’s location is very precisely determined and presented as a level signal by the transmitter. Key advantages of this technology are that the signal speed is known and constant with process variables such as temperature and pressure, and the signal is not affected by foam, beam divergence, or false echoes. Another benefit is that the only moving part is the float that rides up and down with the fluid’s surface.