GB751852A - Improvements in or relating to the measurement of physical values - Google Patents

Abstract

751,852. Electric indicating systems. TINSLEY (INDUSTRIAL INSTRUMENTS), Ltd., and STEGHART, F. L. F. Feb. 15, 1954 [Feb. 27 1953], No. 5613/53. Class. 40(1) A variable, e.g. fluid-flow, pressure, temperature or electric current, is measured translating it into a corresponding force which is automatically balanced by a counter force controlled by an electric current derived from an electromagnetic pick-off responsive to force unbalance and amplified in a magnetic amplifier. Further thermionic amplification may be provided, and the amplifier current output which may provide the counter force electromagnetically, may serve to indicate or control the variable in question. As shown, the rate of fluid flow in a pipe 1 is converted by a venturi 2, diaphragm 4 and a mechanical amplifying lever system 10-15 into a corresponding displacement of a lever 7 about its pivot 8. The lever 7 carries a coil 18 movable along the core leg 19 of an A.C. electromagnet 20 in such a way that the e.m.f. induced in the coil varies in magnitude and phase sense according to the magnitude and sense of the displacement of the lever 7 from a neutral position. This control voltage is fed through a rectifier 23 to the control windings 25, 25a of a magnetic amplifier 24. The amplifier energizing and output windings 27, 27a are series fed from a transformer 22-26 and through a rectifier 30 supply positive feed back windings 29, 29a to increase the amplification. Through a further rectifier 28 the output A.C. windings supply a corresponding pulsating D.C. through coils 34-36. The coil 34 is carried by the lever 7 and moves in the gap of a magnet 35 energized by the coil 36 until the two torques exerted on the lever 7 balance one another when the current in the coils 34-36 is a measure of the fluid-flow and is indicated at 31 recorded at 32 and integrated at 33. Since both coils 34-36 are energized by the output current the meter reading at 31 is directly proportional to fluid flow. The rectifier 28 may be dispensed with if moving iron instruments are used. In a modification (Fig. 2, not shown), a thermionic amplifier is disposed between the magnetic amplifier and the output circuit 31-35. Temperature may be measured by using a bimetallic strip to actuate the lever 7, or the current produced by a thermocouple or resistance thermometer may be supplied to a D.C. electromagnet which actuates the lever 7. Electric current may be measured by applying it to this magnet.