GB1459177A - Sequential control systems - Google Patents

Abstract

1459177 Sequential control MACHINE TOOL INDUSTRY RESEARCH ASSOCIATION 1 Feb 1974 [3 Nov 1972] 50746/72 Heading G3N In a sequential control system, memory M1 stores, at each of its memory locations, an allowable combination of signals which may derive from a controlled machine or process, a corresponding location of memory M2 storing a combination of output signals to be generated in response to the particular combination of signals from the controlled machine or process. The latter signals are fed to comparator C, and a high frequency pulse generator P controls binary counter BC, addressing in sequence, locations of memories M1 and M2. When the content of the addressed location of M1 coincides with the combination of signals currently deriving from the machine or process, gate G is inhibited to stop the scan, the signal combination appertaining to the addressed location of memory M2 being fed to control the performance by the machine or process of the next step of the sequence. Consequent upon such step being performed, coincidence no longer prevails, and scanning recommences. During scanning, either the combination of signals from each location of memory M2 is fed to the machine or process, but at too high a rate to generate a response, or, alternatively, such signals may be inhibited from reaching the machine or process until scanning stops. An alternative sequence, defined by the content of the locations of memory M3 may be used, e.g. in emergencies. Each signal of the combination is a binary digit, which for feeding to the comparator, may derive from limit switches, and possibly include digits from controller operated push buttons or switches, and, to control the machine or process may, after amplification, operate valves, relays, or contactors. Sequences can be changed by alteration of the contents of the memory M 1 and M 3 locations. The memories may be of the read-only type, and may comprise magnetic core, or semi-conductor, units.