GB746601A - Improvements in or relating to sequence-operating control systems for electric motors and control switches for use in such systems - Google Patents

Abstract

746,601. Control of several motors; controllers; snap-action switches; electromagnetic switches. BROOKHIRST SWITCHGEAR, Ltd., and ROBERTS, W. E. Aug. 11, 1954 [Aug. 26, 1953], No. 23515/53. Classes 38(3) and 38(5) Relates to a sequence control system for a number of electric motors, means being provided for the operation of each motor in sequence, the stopping of the sequence at any motor or the by-passing of any motor in the sequence, and for automatic .operation so as to pass on the sequence from motor to motor. Each motor has a control unit 1P, 2P or 3P comprising a solenoid 2 with a plunger 3 secured to an extension 3a and a cam 5. An indicating knob 4 having a cross-bar 4a enables the cam to be pushed in, pulled out, or turned for the selective operation of a number of micro-switches 8a, 8b. The rotation of the cam may be limited by means of mechanical stops and means may be provided for holding the cam in any of its set positions. To prepare the system for numerical sequence operation of all the motors, the control units are set with their push knobs 4 in the inward positions and their cross-bars 4a vertical. Closure of a control switch CS energizes the contactor coil 1C for the first motor through contacts 11, 12, whereupon limit switch 1LS closes and maintains the circuit of coil 1C independently of the unit 1P. At the same time, an interlock relay 1R is energized to open contacts 1R1 and close contacts 1R2, a lamp SP indicating that the sequential operation is proceeding. The closing of the limit switch 1LS also energizes the reset coil 2 of the unit 1P so that it is returned to the position shown, and, when the first motor has completed. its cycle of operation, the switch 1LS opens to deenergize that motor and re-set the relay . 1R. This completes the circuit to the contactor 2C of the second motor which runs through its cycle of operation in a similar manner. At the end of the whole sequence, the lamp SP is extinguished and a lamp SC indicates that the sequence is completed. To stop the sequence at a desired point, the push-knob of the appropriate control unit is turned so that the crossbar 4a is horizontal. If the knob is not depressed the sequence will continue up to the preceding motor and will then stop. If the knob is depressed, then that particular motor'will carry out its cycle of operation at the end of which the push-knob is ejected to stop the sequence at that point. To by-pass a particular motor, the appropriate push-knob is left in the "out" position with the cross-bar vertical. The cycle of operation of any motor may be repeated by stopping the sequence at that point, depressing the appropriate control knob, and then turning it to the vertical position. Alternatively, the sequential operation of all the motors may be completed and the operator of a particular motor repeated by the appropriate actuation of its control knob. An application is described to a soot blower installation comprising electric motors for the manipulation of the soot blowers as well as for the operation of steam or air control valves at appropriate times (Fig. 8, not shown). The system comprises a supply unit, a valve control unit, limit switch mechanism for the valve and blower motors, and a control panel. The blower motors operate one at a time, and, if a blower motor is overloaded, the steam valve is closed and an alarm bell sounded. An isolating switch allows one valve to be isolated for maintenance, and an interlock device enables the blower sequence to be tested without opening the steam valve. A torque switch trips if there is an obstruction during valve-closing operation, a further switch disabling the electrical drive of the valve and permitting hand operation. The control units used in this installation have a closing solenoid in addition to the re-set solenoid (Fig. 9, not shown), and the pushknob has mechanical means for preventing its depression, if so desired. A timer for "cracking" the valve is provided, and blowing operations can commence only when the steam supply is at the appropriate temperature and the steam valve is fully open. The system may be modified for control of a long-stroke blower having forward and backward limit switches, and an air heater blower, having a timer and means for stopping the air blower in one position for the required period, as well as a blower of normal type (Fig. 11, not shown).