What is the reason for the vent tube in the cable of the series 612 and 627 submersible level transmitters?
A. All pressure measurements are inherently differential in theory. Gauge pressure is referenced to ambient atmospheric, absolute pressure is referenced to vacuum contained in an evacuated chamber within the transmitter. The level measurement is also a differential measurement, with its reference to ambient atmospheric pressure. In order for the submersible level measurement to be referenced to atmospheric, the cable contains a vent tube which runs the complete length of the cable and “vents” into the atmospheric pressure at the junction box connection which is out of the liquid.
