Patent GB-761565-A (GB)
Title: Improvements relating to the control of air-conditioning apparatus
Inventor: NIXON LESLIE REGINALD
IPC: F24F11/00
Filed: 1953-10-21
Abstract: 761,565. Automatic temperature and humidity control. STONE & CO. (DEPTFORD), Ltd., J. Oct. 14, 1954 [Oct. 21, 1953], No. 29077/53. Class 38 (4). An air-conditioning device has as condition-sensitive means a bridge network comprising temperature-sensitive and humidity-sensitive elements. The invention is described with reference to a railway carriage, Fig. 17, in which a fan 13 circulates fresh air from 14 mixed with recirculated air from duct 16 over cooling means 12 employing compressor 10. A variable damper 18 controls the humidity and air heaters 19, 20 the heating of the air, the bridge being situated at 21. One suitable bridge, Fig. 1, comprises temperaturesensitive element T<SP>1</SP> and humidity-sensitive element T2, both of which are preferably of resistive form having negative temperature coefficients and control resistor R<SP>1</SP>. Resistor R<SP>2</SP>, preferably variable, determines the ratio of the control exerted by the variations in the resistive values of T<SP>1</SP> and T<SP>2</SP> and these are indicated by the magnitude and phase, either 0 or 180 degrees, of the signals at terminals DC relative to an applied A.C. at terminals AB. After amplification these are applied at CD<SP>1</SP> to a discriminating network, Fig. 4, comprising two pentodes V<SP>1</SP>, V2 whose anodes are energized in push-pull from the same A.C. source and one of which is rendered conductive, according as the A.C. potential existing across CD<SP>1</SP> is in or out of phase with the applied A.C., to energize one of the anode load relay controls R<SP>1</SP>1 or R<SP>1</SP>2 which indicate that the effective temperature is too high or too low respectively and the contacts of which are shown as P, O, N and G, H, I in Fig. 12. These are operated sequentially at increasing values of current to control heaters H<SP>1</SP>, H<SP>2</SP> and H<SP>3</SP> or cooling means comprising compressor motor K and damper motor J controlling by-pass 17, Fig. 17, to an extent determined by whether one or both of contacts H and I are operative or inoperative. A limit switch controls the fully open damper position and speed control means M, e.g. a rheostat, may also be used to control the speed of motor K. In a modified discriminator, Fig. 6, A.C. grid bias is employed to increase the control exerted for a given error. In an alternative form of discriminator, Figs. 7, 9, which employs opposed ring modulators M<SP>1</SP>, M<SP>2</SP> control signals produced at A<SP>11</SP> or B<SP>11</SP> energize either of relay controls R<SP>1</SP>1 or R<SP>1</SP>2. Alternative bridge networks are shown, Figs. 13, 14, giving a constant output voltage at terminals CD over a range of variation of phase of that voltage which may be used to actuate cooling or heating means 25 and 26, Fig. 15, through an amplifier 23 and thyratron output stage 24. Further, two bridge circuits 22 may be used, Fig. 16, each controlling either heating or cooling means, a 90 degree phase change being produced in each of the paths by devices 27, and the relays 28 may be interlocked as shown.