Patent GB-799407-A (GB)
Title: Improvements in or relating to stage lighting control apparatus
IPC: H05B39/04
Filed: 1956-01-12
Abstract: 799,407. Control systems for stage lighting. SIEMENS-SCHUCKERTWERKE AKT.-GES. Jan. 26, 1956 [Jan. 12, 1955; Nov. 5, 1955], No. 1171/56. Class 38 (4). [Also in Group XXXIX] In a stage lighting control system employing magnetic amplifiers MV1, the load windings 1, 2, of each amplifier are connected through positive feed-back windings 3, 4, and rectifiers G1 to a load L1. Negative feed-back is effected with the aid of resistor 16. The load current is supplied from an A.C. source RSTO through a transformer 20 which has the effect of maintaining a constant supply voltage for the apparatus. Windings 5, 6 are provided for auxiliary A.C. magnetization of an amplifier, these windings being connected through resistor 7 to the supply phases S, O, and it is possible to reduce the load current substantially to zero with the aid of such auxiliary magnetization of the amplifier. The resistor 7 may be replaced by an air-gap choke coil, or by a combination of chokes and resistors to provide a predetermined phase position of the auxiliary magnetization current. The auxiliary windings of a number of amplifiers may be connected in series and supplied in common. The premagnetization windings 8 are supplied from a D.C. source and are connected in series with a high resistance 10, high resistance termination of control windings 9 being effected by resistors 11 and variable resistors 12, whereby the time constants of these circuits are reduced. In. addition to the use of alternating-current auxiliary magnetization, the magnetic amplifiers have cores consisting of alloys having one or more preferred magnetic directions and constructed to avoid constriction of the flux path. Each variable resistance 12 is connected to one of three control lines joined to magnetic amplifiers MV. The amplifiers have group-setting devices 13 and a fader 14 for altering the brightness of one group of lamps. All the lamps may be disconnected in common or may undergo a common reduction in brightness by means of circuit element 15 which simultaneously controls all the amplifiers MV. In another arrangement, the auxiliary alternating-current is supplied by transformer 21 through resistors 23, the pre-magnetization windings 8 being energized through rectifier 24 and adjustable resistance 25. Individual adjustment for each amplifier may be provided by tappings in the windings 8, and by means of shunt resistors 26. The use of negative feedback for the amplifiers derived from the output voltages enables the characteristic curves connecting control current and output voltage to be substantially coincident for different loads. Positive feedback derived from the load current increases the slope of the lamp-voltage-control current characteristic when the load resistance has a low value. The member for adjusting the control magnetization of an amplifier may be coupled with means for varying the auxiliary alternating- current so that these quantities are simultaneously controlled in different senses. Special arrangements for the control and pre-magnetization windings involve the disposition of the operating winding 1 between two components of the control winding 9, and the placing of the pre-magnetizing windings 8 partly above and partly below the operating winding 1. Any reduction in the heat transfer rate due to these special arrangements is obviated by overdimensioning the amplifier, Fig. 7 (not shown).