Patent GB-839574-A (GB)
Title: Improvements in or relating to signal control circuits
IPC: H04N5/268
Filed: 1956-11-26
Abstract: 839,574. Television. FERNSEH G.m.b.H. Nov. 26, 1956 [Nov. 26, 1955], No. 36094/56. Class 40 (3). Television signals from one or more of a plurality of channels, of which only two, K<1> and K<11>, are shown, may be switched to a common output 3 by means of a control circuit comprising a push-button S<1>, S" associated with each channel and relays A-E. Each channel includes a valve V<1>, V" which is cut off at its suppressor by bias from a negative source 5 and the switching is effected by allowing the suppressor to return to E potential. Each suppressor circuit includes a capacitor 6<1>, 6<11> and instantaneous, X- or V-fades between channels are provided by choice of appropriate time constants for the charge and discharge paths of the capacitors. Each channel includes also a potentiometer M<1>, M<11> for manual control of fades, the potentiometers being provided with limit contacts BL<1>, BL<11> and TL<1>, TL<11> which operate when the potentiometer sliders are moved from the fully off and set at the fully on positions respectively. The apparatus has the following characteristics :-(1) each channel may be connected to the output by operation of the appropriate push-button; (2) the operation of any push-button disconnects any other source previously connected; (3) two channels may be brought into operation by operating the associated push-buttons simultaneously or by bring- ing both channels into operation on manual control; (4) movement of any manual control from the OFF position fades in the associated channel and causes the disconnection of any other channel not on manual control; (5) the manual control of any channel already connected to the output may be brought into operation by advancing the control to the fully ON position; (6) the connection of all channels may be terminated by operation of an OFF button O. Detailed operation. Switching a source to the output.-The associated push-button, e.g. S<1> for channel K<1>, is operated and causes relays A<1>, B and C to operate in series. Contact All then discharges capacitor 6<1> through resistor 7<1> to allow valve V<1> to become conducting and connect channel K<1> to the output 3. Contact A<1>2 completes a holding circuit for relay A. A contact of relay B is included in the holding circuit of the A relay of each channel and the operation of the relay thus releases any other channel previously connected. Relay B releases more rapidly than relay A<1> so that the relay remains operated over the hold circuit after the pushbutton is released. The operation of relay C provides a charge path through a resistor 8 for the capacitor 6 in any channel previously connected. The value of resistors 7 or 8 are made equal to provide equal fade-in and fade-out times for the channels. The times are such as to produce substantially instantaneous fades. To provide for other types of fade, e.g. an X- fade where one channel fades out as the other fades in, both being operative simultaneously, or a V-fade where one channel fades out fully before the other fades in, further groups of relays A, B, C and push-buttons are provided. Manual control.-To fade in an initially inoperative charnel, the associated potentiometer, for example potentiometer M<1>, is advanced from its OFF position. Contact BL<1> then closes and operates relay D which complete a circuit to discharge capacitor 11<1> through relay E which operates and holds over E<1>2. Contact E<1>1 brings the channel into operation by discharging capacitor 6<1> via potentiometer M<1>, and contact E<1>3 discharges capacitor 15 through relay F which operates momentarily to break the holding circuits of all the A relays and thereby release any channel previously connected. Relay F releases more rapidly than relay E so that relay E remains held over the circuit via contact E<1>2. When a channel is already in operation it may be brought on to manual control by advancing the potentiometer to the fully ON operation. Relay D<1> operates over contact BL<1>, but relay El does not operate until contact TL<1> closes. The operation is then transferred to manual control when relay F operates and releases the A relays. Simultaneous operation of two channels.-This may be effected by operating two push-buttons simultaneously, the two A relays remaining held over their respective hold circuits. Alternatively, if one channel is in operation on manual control, a second may be brought in on manual control by advancing the associated potentiometer. Relay F does not operate to release the first channel under these conditions since capacitor 15 remains discharged over the E<1>3 contact of the first channel relay. Termination of all connections.-OFF button O is operated and completes a circuit for the B relay independent of all other relays. The holding circuits of all A and E relays are then broken and all operative channels released.