GB1174091A - Cyclic Monitoring System for Electrical Devices - Google Patents

Abstract

1,174,091. Selective signalling. COAL INDUSTRY (PATENTS) Ltd. 3 Feb., 1967 [4 Feb., 1966], No. 5022/66. Heading G4H. A plurality of remote switch units, each including a single switch (e.g. along the face of a coal mine) are scanned cyclically and repeatedly, operation of any switch, or the occurrence of a fault, terminating each scan prematurely and turning-off a motor. The position at which the premature termination occurred is indicated centrally by lamps. The switch units, which comprise principally a transistor, a Zener diode and manually operated switch contacts, and which function as monostable circuits are so arranged that when all the switches are unoperated, they are connected in series. The application of a pulse to the first switch unit in the series then turns it " on " and after a short time it reverts to its stable condition and in so doing turns on the next switch unit, and so on until the end of the chain is reached. Each time a switch unit reverts to its stable state a pulse travels back via the series connected units to the central equipment where it is counted. At the end of a scan cycle one pulse will have been produced by every switch unit and a count equal to the number of switch units indicates that no switch count has been operated manually and that no fault has developed. Under these circumstances the motor control circuit is energized. If, however, any switch count is manually operated, then the series connection between it and the next switch unit is broken, and also its time constant is increased by a factor of about six. Thus a scan of the switch units will now terminate prematurely at the manually operated switch and the number of pulses counted will indicate its position. Also the last pulse received was a certain period later than usual. In these circumstances the motor control circuit is not energized. If a fault occurs which prematurely terminates a scan, the count reached will indicate its location and the fact that the last pulse to be counted was not a particular period later than the previous pulse will indicate that a fault has occurred. A fault indication is then given.