GB1248563A - Electrical flowmeters - Google Patents

Abstract

1, 248, 563. Measuring fluid-flow electrically. PERKIN-ELMER Ltd. Oct. 15, 1968 [Oct. 19, 1967], No. 47611/67. Heading G1N. A fluid-flowmeter includes; a thin-walled, tubular, metal duct 1 which is maintained at a temperature above ambient by means of heating coils 3-3A and 5-5A closely wound about it, a brass heat sink 2 which maintains the two ends of the duct at a constant temperature and temperaturesensing coils 4-4A and 6-6A wound bifilar with heating coils 3 and 5 respectively. In the absence of flow the temperature gradient along the duct is symmetrical about the mid-point but a flow of fluid causes downstream heat transfer which renders the gradient asymmetric. The heating and sensing coils may form the four resistance arms of a bridge circuit when the gradient asymmetric. The heating and sensing coils may form the four resistance arms of a bridge circuit when the unbalance voltage may be calibrated in terms of fluid-flow. In Fig. 2 (not shown) the duct is arcuate. In Fig. 4 (not shown) two similar flowmeters are mounted in a common heat sink (12-14) for use with a twin-column gas chromatograph. The heating and sensing functions may be discharged by a single centre-topped coil or heating may be achieved by passing a current through a duct wall. Another embodiment uses conductive layers instead of coils. The coils or layers are insulated from each other and the duct by oxides of beryllium, silicon or aluminium. The heat sink temperature may be regulated by an automatic control system. An alternative form of the embodiment of Fig. 1 has an electrically insulating layer between an end of a duct and the heat sink.