Thermal dispersion switch with self test circuit

摘要

A thermal dispersion flow/level switch includes a dual element probe assembly. Each element comprises an RTD sensor. The two RTD's are driven at different currents at a fixed ratio so that one RTD is self heated to establish a temperature differential. When a process product comes in contact with the heated sensor, the thermal differential is diminished. The differential is set to determine presence or absence of a process media and provide a change of contact state responsive thereto. In a flow application under no flow or low flow conditions, the RTDs will stabilize with a sufficient temperature differential which decreases in response to higher flow rates.