| 摘要 |
1292457 Automatic control ARMOUR & CO 10 Nov 1969 [12 Nov 1968] 54867/69 Heading G3R Deviation of a variable outside a desired range of values in one sense causes energization of a plurality of controllers to apply incremental corrections in succession at intervals until the variable is restored within the range, deviation outside the range in the opposite sense being corrected by successive de-energization of the controllers. In Fig.1, five ammonia compressors A-E, each having four stages 1-4, operate in cascade. The high initial suction pressure closes a switch to operate a timer in a unit 18 to generate increase demand pulses at one minute intervals which are transmitted over a line 19 to operate delayed relays causing the compressors to start up and unloading valves of the compressor stages to be de-energized in succession until the suction pressure falls below a predetermined range. Operation of the relay of each stage completes the control and power supply circuits for the relay of the next stage. When the suction pressure has fallen below the predetermined range it closes a switch to operate a second timer in unit 18 to generate decrease demand pulses at five minute intervals which are transmitted over a line 20 to stop compressors and energize unloading valves of the compressor stages in succession until the pressure rises above the predetermined range. The next reduction of pressure is then effected by a five minute timer instead of the one minute timer which is used only for the initial reduction. Switches are provided to select the number of stages which are to be automatically controlled and other switches permit stages to be rendered operative manually. Relays in a unit 21 disable the system and/or operate indicators or alarms upon power supply failure, low compressor coolant pressure, high level in the accumulator, high condenser pressure or extra high or low suction pressure. Use of solid state switches is referred to. |
