Calorimetric flow monitor

Claim 1

A calorimetric flow monitor for monitoring the flow of a medium through a pipe, comprising, in combination: a measuring head including a metallic sleeve having an external thread via which said head can be tightly screwed into a threaded bore of such pipe in a manner such that one end of the said sleeve is directed toward the medium and the longitudinal axis of said sleeve is perpendicular to that of the pipe, an insulating block tightly closing the one end of said sleeve and protruding from the one end of said sleeve, said block being provided with two through bores extending in the direction of the length of said sleeve, two pins each tightly fitted inot a respective one of said through bores at the end of said block which protrudes from said sleeve, said pins protruding from said block and being of a material having a high thermal conductivity and each said pin being formed to have a blind bore, first and second tubular, heat conductive sleeves each disposed in a respective one of said blind bores, first and second thermistors each disposed in a respective one of said blind bores and located within a respective heat conductive sleeve while being insulated therefrom, a heating coil wound on said first heat conductive sleeve for heating the respective thermistor in said first heat conductive sleeve, and a casting resin having good heat conductivity filling each of said blind bores for establishing a good thermal communication between each said thermistor and the flow medium when said head is disposed in a pipe through which such medium is flowing, whereby heat supplied to said first thermistor by said heating coil can be carried off by the medium and said second thermistor can be brought to the temperature of the medium; means defining an electrical bridge circuit including said thermistors; first and second differential operational amplifiers each having a pair of inputs connected at selected points of said bridge circuit; first signal processing means connected to the output of said first differential amplifier for deriving from the output signal therefrom an indication of increases or decreases in the medium flow speed from a predetermined value; and second signal processing means conducted to the output of said second differential amplifier for deriving from the output signal therefrom an indication of breakages in the connections to said heating coil and said first and second thermistors.