Patent GB-606103-A (GB)
Title: Improvements in and relating to temperature compensation for direct current telemeters
IPC: G08C19/02
Filed: 1943-11-17
Abstract: 606,103. Temperature compensation. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 17, 1943, No. 19165. Convention date, Nov. 21, 1942. [Class 37] A receiver for a D.C. telemetering system, in which indications are produced by varying the relative proportions of low temperaturecoefficient resistance in two circuits, comprises a pair of angularly-disposed coils of wire having an appreciable positive temperature coefficient, a movable magnetic element in inductive relation to these coils adapted to deflect away from a mid-position by an amount depending on the ratio of the currents in the coils, and a temperature compensating arrangement comprising means decreasing in strength with temperature rise for magnetically attracting the movable element towards the mid-position to an extent decreasing with rise in temperature. Fig. 1 shows a telemetering system comprising a transmitter 11 and a receiver 12. The transmitter comprises a potentiometer resistor 14 with terminals 15, 16 and a slider 17 adapted to move in response to variations in an indication to be transmitted to the receiver 12. The receiver 12 comprises a cylindrical rotor 19 of material of high coercive force magnetized along a diameter and a stationary member consisting of a pair of angularly displaced coils 20, 21 with a core structure in the form of an annular or hollow cylindrical shield 22 of high permeability low hysteresis material. The coils 20, 21 are of insulated copper or similar wire and cause radial magnetic fields of the same polarity. The coils 20, 21 are connected to the terminals 15, 16 and have a junction terminal 27 connected to one terminal of a battery 13, the other terminal of which is connected to the slider 17. The resistance 14 is of wire having a low or zero temperature coefficient, so that when the slider 17 is moved from the position of balanced currents in the coils 20, 21 the temperature effects in these coils are unequal because the circuits contain different proportions of wire of positive and zero temperature coefficient. To compensate for the error due to this a magnetic element 34 is mounted between the coils 20, 21 and is composed of a material having a negative coefficient of permeability. At low temperatures the nearest pole of the rotor 19 is attracted towards the element 34, but as the temperature rises the permeability of this element falls, and the attractive force between the rotor 19 and the element 34 decreases. In a modification, Fig. 3, the coils 20, 21 are overwound with coils 35, 36 in thermal relation with them. The junction 37 of the coils 35, 36 is connected in series with a resistance 38 to the slider 17, so that the coil 36 is in series with the coil 20 and the coil 35 is in series with the coil 21. As the coil 20, for instance, is increased in resistance by self-heating so as to draw too little current, the resistance element 36 in the branch circuit also rises in resistance and diverts less current from the coil 20. The Specification as open to inspection under Sect. 91 states also that the coils 35, 36 may be resistance units of positive temperature coefficient without indicative effect. This subject-matter does not appear in the Specification as accepted.