Patent GB-1311790-A (GB)
Title: Positioning means
IPC: F15B9/00
Filed: 1970-12-31
Abstract: 1311790 Thermal electric meters; indicating apparatus; electric control systems FOXBORO CO 31 Dec 1970 [12 Jan 1970] 62065/70 Headings G1J G1N and G1Q [Also in Division G3] Apparatus for positioning an output member in dependence on the magnitude of an electric input signal comprises a wire anchored between members so mounted that their separation changes as the length of the wire changes due to variations in its temperature, the changes in length of the wire controlling changes in the position of the output member, a control unit for adjusting the temperature of the wire in accordance with the input signal, and a feedback device arranged to have on the control unit an influence which is dependent on the position of the output member and which opposes the influence of the input signal. The wire is made of a nickel-titanium alloy which contracts with increasing temperature over a particular range. Pointer-type thermal electric meter, Fig.3 The wire 30 extends between a fixed anchor 34 and, via an overload spring 36, a member 38 pivoted about an axis 16 and coupled to the pointer  pen 14 of a chart recorder. A spring 40 holds the wire in tension. The D.C. input signal E i  is chopped, amplified (72, 74) and applied to the wire to heat it. A transducer 54 whose inductance varies with pointer position is connected in series with a resistor 78 across the output of an oscillator 76 to produce a feedback signal which opposes the input signal E i  at a summing junction 64. Zero is set by adjusting a bias signal (68) also fed to the summing junction. Ribbon-type thermal electric meter Fig.7 The wire 30 extends between a fixed anchor 198 and a hub portion 194 of a rotatable spool 184 which is biased by a spring 193 so as to hold the wire in tension. A ribbon 182 held in tension by a spring 192 is coupled to the spool 184 so that the position of a coloured portion 181 of the ribbon relative to a fixed scale varies as the spool position varies. The wire is heated by a constant current (202). The electric input input signal E i  is applied to a force motor 214 whose armature is coupled to a pivoted heat sink 204, the position of which determines the temperature of the wire. Mechanical feedback is provided by a spring 212, fixed at one end to the spool 184, which applies to the heat sink a force dependent on the angular position of the spool, in opposition to the force provided by the force motor 214. Valve-positioning servosystem, Fig. 8 The wire 30 extends between two auxiliary valves 258, 264, the first of which (258) opens when the wire contracts to cause the pressure in a chamber 256 to increase, the second (264) opening when the wire expands to cause the pressure to drop. The pressure in the chamber 256 controls the position of the main valve 262. The system is otherwise generally similar to Fig. 3; in the steady state both auxiliary valves remain closed, the feedback signal exactly balancing the input signal. Angular position sensor, Figs. 3, 5 An angular position sensor comprises a coil wound in two parts 166, 166<SP>1</SP>, on a shell-type core 160, 160<SP>1</SP>, and a conductive vane 56 which extends through a gap 164 in the centre limb of the core and which takes up a position dependent on the angular position to be sensed. The variations in the shading effect of the vane vary the inductance of the coil.