711,515. Control of D.C. motors. OTIS ELEVATOR CO. Jan. 21, 1952 (Jan. 27, 1951], No. 1632/52. Class 38(3) [Also in Group XXV] A power-operated door giving access to a lift cage carries a gas-filled thermionic tube provided with a control and means are provided (a) for applying across the anode-cathode circuit of the tube voltage of a value above sustaining value but insufficient to cause breakdown of the tube, (b) responsive to a person moving into the path of the door for applying between the control and a point in the anode-cathode circuit a difference in potential of recurrent impulses sufficient to cause breakdown of the tube, and (c) responsive to said breakdown to control the operation of the poweroperating means to stop the closing of the door to protect said person. The lift cage door and the respective lift shaft doors, all of which are of the sliding kind are operated by an electric motor carried by the lift cage. The shaft doors carry at their leading edges electrically insulated metallic channels HSG which close against corresponding fixed channels HPG. The cage door carries at its leading edge an insulated, metallic channel CSG which closes against a corresponding fixed channel CPG. The channel CSG is composed of angles 80, 81, Fig. 6, covered with insulation 82, and houses three spaced-apart tubes DPT. Each of the latter contains a cathode 101, and anode 102 and a control electrode DPTE, and has an external metallic area CS adjacent the anode. The leading face of the channel is covered by a plate 120 of insulating material, such as lucite, grooved internally at 121 to accommodate, at each tube, a plate antenna CA which is flanged towards the shaft door,-angle 81 being cut away at 91 in the region of the antenna. The latter has a metal stud 112 connected by a spiral spring 113 to the metallic area CS. A tab 115, secured between the antenna and stud affords connection to the control electrode. The tube fits in a socket 105 secured by screws 107 to metal posts 106 welded to angle 80, the screws affording means for applying electrical potential to the channel. Operating circuits, Fig. 10, are provided with A.C. potential from leads W11, 12, the latter being earthed at GR. Fig. 105 shows in spindle form the operating relay coils and their corresponding contacts, the latter in the positions they assume when the coils are de-energized, and the coils and contacts being aligned with the positions they occupy in Fig. 10. The coils are denoted by alphabetical symbols and the contacts by numerals added thereto. The secondary of a transformer SGT applies potential to the channels HSG, HPG, and also to the primary of a transformer DPDT. The earthed side of the secondary of the latter is connected by a rectifier EDP' to the cathodes of the tubes, the other side of the secondary being connected to the channels CSG, CPG, and to the anodes of the tubes through the coil DP of a door protective relay. The control electrode DPTE of each tube is connected to the metal spot CS, to the corresponding antenna CA, and adjustably to an intermediate point of a voltage divider resistance RVD. The potentials applied to the anodes and control electrodes are so adjusted that discharge through the tubes is prevented. An auxiliary protective relay DPX is also connected across the secondary of the transformer DPDT. The control circuits for the door-operating motor are supplied with D.C. potential through a rectifier EDC. When the hoisting motor operates, a relay coil (not shown) is energized to open contacts H1, H3 and close contacts H2, H2<SP>1</SP>. The protective circuits are then disconnected, and normal time relay NT, auxiliary time relay XNT and delayed time relay DT are energized. When the lift stops at a landing, contacts H2, H2<SP>1</SP> open to disconnect coils XNT and DT, but the former remains energized for 3 seconds longer through condenser QXNT and the latter for 15 seconds longer through condenser QDT. A set coil of door relay DR is energized through contacts XNT1 and H3, and the relay latches itself in operated position to close contacts DR2 to energize door opening relay DO through door open limit switch DOL. Contacts DO4 then open, contacts DO5, 6 close to energize the door-operating motor armature DMA through resistances RDM3, 4, and contacts DO2 open in the circuit of door closing relay. DC. A rectifier EDB is connected across the armature by contacts DC3 when the doors are opening, but with a polarity to prevent the flow of current therethrough. After some movement of the doors, speed limit switch DEL closes to energize speed relay DE which closes contacts DE3 to short circuit resistance RDMF in the circuit of the motor field winding DMF, and also closes contacts DE4 to short circuit resistance RDM4. Switch DEL opens when the doors approach their fully open position, but relay DE remains energized through contacts DEI and DO1. Door open limit switch DOL opens when the doors are fully open to de-energize relay DO which opens contacts DO5 6 to break the armature circuit. Contacts DO1 also open to deenergize relay DE which closes contacts DE5 to short circuit the armature. Relay XNT operates 3 seconds after the hoisting motor stops to open contacts XNT2 and thus disconnect relay NT which remains energized for a further 3 seconds through condenser QNT, when contacts NT1 close to energize a re-set coil in relay DR through contacts DR1 to unlatch relay DR which opens contacts DR2 in the circuit of relay DO. The door closing relay DC is then energized through the door closing limit switch DCL and contacts DP2, DO2 and NT1 to close contacts DC2, 4 and open contacts DC3 to energize the motor armature through resistance RDM1, contact DO4, part of resistance RDM5 and contacts DE6. After some movement of the door, switch DEL closes to energize relay DE, when contacts 'DE3 close to short circuit resistance RDMF, and contacts DE6 open to remove the short circuit from resistance RDM5. Switch DEL opens when the doors are nearly closed, but relay DE remains energized through contacts DE2 and DC1. As the doors reach closed position switch DCL opens to de-energize relay DC, when contacts DC3 close to shunt the motor armature through the braking rectifier EDB, contacts DC2, 4 open to disconnect the armature, and contacts DC1 open to de-energize relay DE which closes contacts DE5 to short circuit the armature. The time lag of relay NT may be cancelled by operating a push button DCB to short circuit the condenser QNT. The presence of a passenger obstructing the closing of the doors causes an increase in capacity between the antenna and earth, thereby effecting discharge of the tubes to energize relay DP which opens contacts DP2 to de-energize relay DC for stopping the motor. Contacts DP3 also close to energize relay DO through switches DCL and DOL and thus cause the doors to open. Contacts DP1 close to energize relay DPX which closes contacts DPX2 to latch relay DR in operated position to close contacts DR2. Contacts DPX1 also close to shunt the tubes through resistance RDPX2 to stop the discharge and to de-energize relay DP, the dropping out of the latter being delayed by a shunted rectifier EDDP to ensure latching of the relay DR. Contacts DP1 then open to disconnect relay DPX, dropping out of the latter being delayed by a condenser QDPX. Relay NT remains connected in circuit through contacts DO3 till the doors are fully open. If the obstruction persists, relay NT is repeatedly energized via contacts DPX3 until relay DT drops out 15 seconds after the hoisting motor has stopped, when contacts DT1 open to render the protective circuits inoperative, and contacts DT2 close to de-energize the de-latching coil in relay DR and to energize relay DC through switch DCL and contacts DP2 and DO2, while contacts DT3 close to short circuit part of a resistance to cause slow operation of the motor in the door closing direction.