Device for measuring and/or monitoring the flow velocity of a flowing fluid

Claim 1

In a device for monitoring the flow velocity of a flowing fluid, comprising: temperature sensing means adapted for location in said flowing fluid, means for supplying constant electrical power to said sensing means so as to obtain a constant temperature excess therein relative to ambient temperature, whereby a temperature reduction in said sensing means caused by said flowing fluid will be related to said flow velocity, the improvement wherein: said sensing means comprises first and second essentially identical monolithic integrated circuits, each arranged in a respective heat conducting case, each of said integrated circuits comprising a crystal carrying a plurality of series connected integrated diodes forming a diode path and serving as a temperature sensor, both of said essentially identical crystals in addition including an integrated semiconductor heating member having a low temperature coefficient, said heat conducting cases being fastened to a sheet located in the flow path of the flowing with the plane of the sheet extending substantially in parallel to the flow direction of the flowing fluid and with said heat conducting cases located substantially in the same plane transverse to said flow direction, a radiation shield mounted on said sheet between said two heat conducting cases, said constant power supplying means includes means for supplying a substantially constant voltage to said heating member of only said first crystal and thereby developing substantially constant power in said first crystal over a large temperature range, means is provided for supplying current in the forward direction in said two diode paths, and a comparison circuit is connected to said two diode paths for comparing the forward-direction currents flowing respectively therein and producing a difference signal corresponding to the difference between said forward-direction currents, said difference signal representing the fluid flow velocity.