Patent GB-1013976-A (GB)
Title: Variable time delay sequencing arrangement
IPC: G05B19/07
Filed: 1963-09-23
Abstract: 1,013,976. Transistor pulse timing circuits. ELASTIC STOP NUT COPORATION OF AMERICA. Sept. 23, 1963 [Oct. 1, 1962], No. 37388/63. Heading H3T. A process-timing circuit comprises a semiconductor relaxation pulse generator producing pulses at spaced intervals, and a double-banked stepping switch actuated by the pulses delivered by the pulse generator, one bank providing for the sequential connection of a power supply to the devices to be operated in the process to be timed and the other connecting appropriatelyvalued resistances in sequence into a resistancecapacitance network controlling the timing of the relaxation pulse-generator so that the period of time for which each device is operated is individually determined by the magnitude of the corresponding appropriately-valued resistance. Commencing the cycle with the wiper arms 64, 66 of the stepping switch 56 in the positions shown capacitor 14 charges through resistors 72a, 76 potentiometer 18 and the base-emitter diode of conducting transistor 22. Transistor 26 is consequently cut off and relay 40 is not energized. Upon an appropriate level of charge occurring in the capacitor 14, unijunction transistor 12 is triggered producing a negative pulse at the base of transistor 22 to cut the same off and render transistor 26 conducting and energize relay 40. Relay armature 42 moves to interrupt the earth connection at contact 42a thus releasing relay 60 which causes armature 62 to move to contact 62b and wiper arms 64, 66 to move to the position b of the stepping switch. The armature 42 then engages contact 42c so discharging capacitor 14. Conduction recommences in transistor 22 after an interval determined by variable resistor 16 so that relay- 40 is once more de-energized and relay contacts 42a, 42b reconnected to earth. Closure of contact 42b supplies power to the device connected between the appropriate one of contacts 70a-70f, and closure of contact 42a re-energizes relay 60 which is initially supplied from supply 48 directly through contact 62b. This winds a spring which moves the stepping switch when relay 60 is released; the armature then moves to contact 62a whereby resistor 50 is included in the circuit after the spring is wound so as to maintain the relay energized at a reduced holding current. Capacitor 14 then charges as before, but this time through a resistor 72b, the operations otherwise being as previously described; this either continues until the full sequence of operations is complete and the switch arms 64, 66 come to rest upon open-circuit contacts or the switch may be arranged to return to the first contact a so that the cycle repeats indefinitely. Certain of the resistors 72, e.g. resistor 72c, may be sensitive to temperature, pressure or humidity so that the length of time for which the corresponding step in the process takes places is dependent upon ambient conditions. Alternatively a limit switch 74 may be provided, this closing in response to the arrival of a mechanical element at a predetermined position, the stepping switch operating thereafter with or without a delay depending upon the setting of resistor 72b. Potentiometer 18 and associated resistor 20 provide an overall timing adjustment which is superimposed upon the individual settings provided by the resistors 72. Resistor 20 may be sensitive to temperature, pressure or humidity to provide a control dependent upon ambient conditions. Similarly resistor 16 which is shown as variable to permit adjustment of the interval between successive steps in the process may be sensitive to external conditions such as temperature. The voltage supply to transistors 12 and 22 is stabilized by resistor 15 and Zener diode 36.