Thermal dispersion mass flow rate and liquid level switch/transmitter

Abstract

A thermal dispersion switch/transmitter for determining flow rate and liquid level in a non-contacting apparatus. A special preparation of one or more small spots in the outside surface of the wall of the conduit, standpipe or container enables one or more thermally sensitive elements to reside very close to the fluid on the opposite side of the wall. A temperature sensor is formed of a raster pattern electrical conductor deposited on a thin, electrically insulative, thermally conductive flat chip. One temperature sensor is time-shared and is periodically self heated and functions as the reference as well as the active or heated sensor of the invention. One alternative is to employ two temperature sensors, one being a reference sensor and the other being the active sensor. An alternative embodiment employs the same construction of one or more small, very thin membrane surfaces to which multiple detectors are mounted inside a probe inserted into the conduit. A second alternative embodiment employs the same construction of a very thin, small area spot on the outside of a probe inserted into a conduit or vessel for flow rate, liquid level, or interface sensing. Other embodiments are shown and described. All of the embodiments employ a miniature temperature sensor with the sensing element being self heated, the switch/transmitter being configured to operate at intrinsically safe, 24 VDC, 4-20 mA input power.