Patent GB-585518-A (GB)
Title: Improvements in and relating to telemetering systems and apparatus therefor
IPC: G01D5/20
Filed: 1945-02-23
Abstract: 585,518. Telemetering systems. BRITISH THOMSON -HOUSTON CO., Ltd. Feb. 23, 1945, No. 4563. Convention date, Feb. 25, 1944. [Class 40 (i)] A system for reproducing motion comprises a receiver having a saturable core stator with a number of A.C. windings and a unidirectional flux magnet rotor, a transmitter also having a saturable core and unidirectional flux magnet, a winding on the core being connected to one receiver winding to produce a torque along one axis varying in response to movement of the transmitter, and a further saturable core means having a winding connected to a second receiver winding to produce a constant torque at right angles to the first so that the receiver operates in response to the resultant of the two. If the two windings 13, 14, Fig. 3, on the saturable core 12 have an equal number of ampere turns, the magnet 10 will assume any position since all parts of the core have the same reluctance. However, if the ampere turns in coil 14 are increased during one halfcycle and decreased during the next, the magnet 10 will seek the position shown where it offers minimum reluctance to the external core flux. This is done by providing a. reactance 16 woundon a saturable core in circuit with coil 14, the strength of the torque developed in magnet 10 depending on the relative positions of a magnet 17 and reactance 16. As shown in Fig. 4, two such systems are used to control the receiver rotor 26. Winding 23 on the upper stator is connected to winding 33 of a pressure transmitter 32 producing a torque-which tends to set the magnet-along the Y axis. Winding 30 on the lower stator is connected to reactance 38 which remains substantially constant and produces a constant torque, which tends to set the magnet, along the X axis tending to move pointer 27 to the centre of the scale. The transmitter comprises a saturable core 41 on which coil 33 is mounted and a pair of permanent magnets one on each side of the core and mounted on a movable support 46 which extends between a diaphragmlike support 47 and the diaphragm end of bellows 48 which respond to the pressure to be measured. The magnets are reversely polarized so that when they are equidistant from core 41 no unidirectional flux is produced in it, and the only torque acting on rotor 26 is that due to reactance 38, causing the pointer to give a mid-scale indication. With decreases of pres. sure, magnet 45 is brought closer to the core and a unidirectional flux is produced in one direction causing the pointer to move towards zero. With increases of pressure, magnet 44 is brought closer and a unidirectional flux is produced in core 41 in the opposite direction, causing the pointer to move over the other half of the scale. Temperature compensation has to be provided for core 35 since the core saturates at a lower flux density and magnet 39 decreases its flux with increase of temperature so that the torque .produced is decreased. A piece of material having a negative coefficient of permeability is placed in the air gap of core 35 so that it shunts some of the flux away from coil 38. With increase of temperature, part 37 shunts less flux and allows more to go through coil 38, thereby compensating for the decreased strength of magnet 39. The transmitter is similarly compensated by providing U-shaped pieces of material 43 having negative coefficients of permeability, surrounding the ends of the permanent magnets so that they divert a portion of the flux of the permanent magnets away from core 41. In order that the pointer should give an off scale-indication if the circuit between transmitter and receiver is interrupted or grounded, a pull-off magnet is provided surrounding the rotor 26.