GB1121129A - Improvements relating to fluid flow measuring and indicating - Google Patents

Abstract

1,121,129. Measuring fluid-flow. CONTACTROL Ltd. Aug. 2, 1965 [Dec. 1, 1964 (2); May 31, 1965], Nos. 48834/64; 48836/64 and 23162/65. Heading G1N. In a fluid-flow measuring device of the type in which the rise in temperature of the fluid when a determined quantity of heat is supplied to it is measured, the measurement is made using semiconductor diodes. The fluid may be heated by a resistor or by a Zener diode. In Fig. 1, resistor 11 is connected to a constant voltage source and temperature-sensitive diodes 16, 17 are connected in a bridge circuit, diodes 16 providing a correction for the ambient temperature of the fluid. In a modification Fig. 3 (not shown) the heater is supplied with pulses at a frequency proportional to the speed of a vehicle on which the device is carried and the flowmeter is provided in the engine fuel supply line of the vehicle to indicate miles per gallon or kilometers per litre. In the circuit shown in Fig. 7 the output from the bridge circuit including temperature-sensitive diodes 100, 101 is supplied to Zener diode heater 107 so that the temperature rise detected by diodes 101 is maintained constant and meter 108 indicates the current, and hence the power, consumed by Zener diode 107. The bridge components are selected so that at zero fluid-flow the current through diodes 101 exceeds that through diodes 100, thus heating the sets of diodes to differing degrees and reducing the Zener diode current to zero. A sensing unit for mounting in a fluid supply line includes an inner barrel portion 22 Fig. 2 (not shown) containing the temperature sensitive diodes 16, 17, which are supported by their leads, and the heating resistor 11, supported between two perforated discs 29. The barrel portion is surrounded by an outer shell 23 defining an annular cavity 30 which provides thermal insulation for the fluid. The shell is clamped to a flange on the barrel portion, and upstream of the flange is a perforated shank portion 25 for equalizing the temperature over the cross-section of the fluid. The barrel is constructed of material having a high electrical and thermal resistance, while the shank, if it is not integral with the barrel, is constructed of material of high thermal conductivity. In the arrangement shown in Fig. 4 fluid entering at 63 is diverted through an inner barrel portion 53A, containing diodes 57, 58 and a Zener diode or resistor 59, and back through an outer barrel portion 50 to a circular groove 52 communicating with outlet 64. The inner barrel portion is of insulating material and the outer barrel portion is lined with insulating material 55, 56.