Level switch with verification capability

摘要

A level switch which may be employed to detect liquid levels within a process vessel has a self validation capability so that manual testing is not required for proper operation and switch calibration. The switch has a pair of sensors for measuring the pressure of the fluid in the vessel at two vertically separated points in the vessel and a processor for calculating the difference in fluid pressure between the two points for generating a differential pressure signal. A processor also combines the differential pressure signal and a static head pressure signal from one of the points to generate a composite output signal from which an out-of-range condition signal for the fluid level can be generated based upon a pre-determined change in the composite output signal.