GB526262A - Improvements in self-balancing potentiometer systems for controlling, indicating and recording variable conditions - Google Patents

Abstract

526,262. Electric systems for correspondence control. MEYER, L. W. (Lewis Engineering Co. and Mrs. Johnson, M. J.). March 10, 1939, No. 7881. [Class 40 (i)] Relates to an automatic indicating recording or controlling system, as for furnace temperature tested by a thermo-couple, involving a slide wire potentiometer automatically balanced as against the thermo-couple, by a reversible electric motor and galvanometer. The motor is controlled by thermionic devices selectively rendered operative by a single light-sensitive cell which is illuminated upon deflection of the galvanometer by a beam passing through a shutter driven synchronously with an A.C. energizing the thermionic devices. The slide wire control 26 may be adjusted by a motor 32, having a field winding constantly energized by A.C., a squirrel cage rotor and pole shading windings 35, 36. The windings 35, 36 are connected to opposed positions of a transformer winding 40 which is inductively coupled to the anode circuits of two thermionic devices 50, 52. The grids of the latter are connected together in a circuit by which they are normally biassed to cut-off potential and a light-sensitive cell 74 is connected so as to raise their potential when it is activated. Light from a source 69 is reflected by the galvanometer mirror through one or other of two pairs of apertures at different radii in a disc 83 rotated by a synchronous motor 84 fed from the same A.C. as the motor 32, so that the cell 74 is intermittently illuminated during opposite phases according to the sense of the galvanometer deflection. Thus only that thermionic device is activated which will cause motion of the motor 32 in a correcting sense : this motion is continuous. In a modification, a vane, carried by a reed vibrated by a magnet carrying a coil fed by the A.C., co-operates with two apertures in the path of the deflected beam to cause a similar operation. The lightsensitive cell may be of the emissive type with a circuit shown in Fig. 1, or of the conductive type, with a suitably modified circuit.