DEVICE AND METHOD FOR DETECTING MASS FLOW RATE OF FLUID

摘要

PURPOSE: To detect the mass flow of a fluid flowing through a duct by disposing an active element coming into thermal contact with the outer wall of the duct on the outside of the duct. CONSTITUTION: A fluid is returned to piping 8 through main piping 8 - an inlet pipe 12 - a U-shaped pipe 34 - and an outlet pipe 14. A thermistor 60 is bonded to a curved part of the U-shaped pipe 34 in the downstream of a passive temperature sensor 52. The thermistor 60 has a resistance variable with the temperature for the purpose of heat exchange and operates in a high resistance region having a large positive temperature coefficient because of steady thermal loss to the surroundings. A small variation of temperature produces a large variation of resistance in that region and the variation of resistance with respect to temperature is higher than 10%/ deg.C, When a gas flow passes through the bonded part of the thermister 60, temperature of the thermistor 60 lowers slightly as it imparts heat to the fluid to cause a large variation of resistance thus increasing the current passing through the thermistor 60 at a predetermined voltage. The current corresponds to the mass flow and the mass flow can be measured accurately by measuring variation of current.