Fluid flow measuring system

Claim 1

A fluid flow measuring system for measuring the rate of flow of a fluid in a first region of a conduit adapted to contain said fluid, said conduit including a second region therein wherein said fluid is substantially stationary, comprising: a first heating element adapted to be thermally coupled to said fluid in said first region, said first heating element producing a first current signal proportional to the power dissipated in said first heating element, a second heating element adapted to be thermally coupled to said fluid in said second region, said second heating element producing a second current signal proportional to the power dissipated in said second heating element, means electrically connected to said first and said second heating elements, including a first potential source, for supplying a substantially constant voltage to said first and said second heating elements, means including temperature sensitive elements thermally coupled respectively to said first heating element, to said second heating element, and to said flowing fluid entering said conduit thereby sensing the ambient temperature thereof, said means for controlling the current to said first and said second heating elements and thereby maintaining the temperature of both said first and said second heating elements at a constant number of degrees higher than the ambient temperature of said fluid, circuit means connected to said first and said second heating elements for comparing said first and said second current signals to produce a difference signal proportional to the difference in power dissipation between said first and said second heating elements, and circuit means connected to said comparing means for squaring said difference signal to produce an output signal, said output signal being substantially linearly proportional to the rate of flow of said fluid in said first region and being substantially compensated for changes in the density of said fluid.