GB571983A - Improvements in and relating to electrical systems for controlling the operation of apparatus and magnitudes of variable quantities - Google Patents

Abstract

571,983. Follow-up control systems. DAVIS, N. R., and SUN-VIC CONTROLS, Ltd. Oct. 5, 1943, No. 16332. [Class 40 (i)] [Also in Groups XIX and XXXV] Temperature &c.-Apparatus is automatically controlled, or a quantity automatically regulated, in dependence upon a controlling quantity which may be time or another quantity, by means of a surface moved by the controlling quantity and carrying a coating or deposit of different conductivity from the surface. The coating co-operates with an electrical control member, which may move in a different direction in accordance with a controlled quantity, to change the conditions in the grid or control circuit of an electronic relay or oscillating valve governing the controlled apparatus or quantity. The coating or deposit may be continuous or broken, e.g. a line drawn by a graphite pencil on a paper chart which may be carried or driven by the clockwork actuated drum of a recording apparatus of known type. The cooperating member may be a conducting stirrup attached to a recording pen so as to make contact with the surface at a point laterally displaced from the pen. It may be the pen itself and it may be periodically lifted upon contact with the surface, if suitable time delay operation of the relay be provided. It may also be constituted by a coil or by two coils adjacent to opposite faces of the chart, their mutual inductance being varied by proximity to the coating, or it may constitute with the coating a variable condenser. As shown, the coating 9 is maintained in contact with a bar 10 which, with the pen 4, is connected across a resistance 30 on a series circuit of a condenser 28, resistances 29, 30 and transformer windings 25, 31 whereby the phase of the voltage and the grid of a valve 20 is varied in relation to the A.C. potential in the anode circuit. The latter circuit comprises a relay winding 24 normally insufficiently energized to open normally closed contacts 23 in series with the heating winding 21 of a furnace. The recorder movement 6 responds to the temperature of the furnace so that when contact is made between the stirrup 11 and the coating 9 the relay 24 opens the contact 23. The chart or coating may be replaced to obtain any desired programme control of the furnace temperature. The recording apparatus may be provided with a pencil in a suitable mounting whereby it may be positioned at will in or out of contact with the surface in any lateral position ; so that for example the controlled quantity may be maintained constant. An electric heater may be associated with the chart, e.g. in the drum, to combat high humidity conditions. Local heating means, such as a pair of heated rollers, may be used with the chart if colloidal graphite be employed.