Patent GB-869407-A (GB)
Title: Improvements in and relating to systems for presenting information
IPC: H04H1/00
Filed: 1960-02-22
Abstract: 869,407. Electric selective signalling systems. TELEVISION AUDIENCE MEASUREMENT Ltd., and JONES, K. Feb. 22, 1960, No. 6140/60. Addition to 868,082. Class 40 (1). A field station, of a remote indicating system as described in the parent Specification, comprises an electronic control means which, on receipt of a predetermined number of interrogation pulses, operates an electronic pulse generating means to return to the central station at least one response pulse indicative of the state of some apparatus at the field station, the said means requiring no mechanical operation after the initial setting. In a general description of the field unit pulses corresponding to interrogation pulses are counted by a " cup and bucket " counter and the potential across the capacitor of the counter is compared to a standard potential. When the two potentials are the same a valve triggers. The duration of the pulse produced is dependent on a capacitor system whose capacitance may be increased by further capacitors being placed in parallel to the first by the control knobs of the apparatus under observation. This pulse activates a device which prevents further line signals from the central station from registering in the field station in this interrogation cycle, and also excites a tuned circuit to produce a sinusoidal wave, whose duration depends upon the condenser system and hence the controlknobs of the apparatus, which is transformed into negative half-cycles and fed back along the telephone line. Tappings on a coil near the tuned circuit may produce initial damping of the sinusoidal wave and a corresponding delay in the transmission of half-cycles. A positive interrogation pulse passes from the secondary winding T2, Fig. 4, of a transformer T. If it is of sufficient magnitude it overcomes the bias on a diode D11 to pass to the grid of a valve V3 where pulses with an excessive amplitude are attenuated by grid cathode conduction. The limited amplitude negative pulse from the anode of V1 passes to a monostable multivibrator stage, V3 &c., which it trips. The negative pulse passes to a differentiator circuit whose negative component is applied to the left-hand grid of a valve V4 which acts as a limiting amplifier stage. The output from the left-hand side of V4 is a positive rectangular pulse, taken from the junction of R6 and R7, and is counted by a " cup and bucket " counter constituted by D4, D5 and C4. Each successive interrogation pulse received by the transformer T results in a corresponding increase in the potential across the plates of C4. The voltage across C4 is applied to the left-hand grid of a double triode V6 forming part of a voltage comparator stage. The wiper of a potentiometer P1 applies a predetermined D.C. bias voltage, to the right-hand grid of V6 (this voltage being equal to the voltage to which C4 would rise after the number of pulses to which the field station should respond have been received). When the voltages on the left and right grids are equal the left-hand side conducts. Capacitor C4 is then discharged through a thyratron V5, the grid potential on the left-hand side of V6 is lowered and conduction ceases. This negative pulse triggers monostable multivibrator comprising the double triode V7 and is also fed back to trigger a further monostable multivibrator stage comprising a double triode V2, so that the right-hand side conducts, for a period sufficient to allow an interrogation cycle to be completed, applying a backing-off voltage to a diode D8 which limits the amplitude of any signals passing through D1 so that they are insufficient to trigger V3. Thus the field station does not count any further interrogation pulses in this interrogation cycle. The time in which V7 remains in its unstable condition is the duration of the pulse produced, depending upon the value of a capacitance C7. The negative-going pulse from V7 passes to the grid of a double triode V8 arranged as a blocking oscillator. The left-hand side of V8 acts as a damping stage, the cathode being connected to earth through a parallel tuned circuit comprising capacitor C9 and inductance L1. Taps are taken from a resistor R19 and connected to the contacts of a multi-position switch SW1. With no signal applied to the left-hand grid of V8 the left-hand section passes a D.C. current. Arrival of a negative pulse from V7 cuts off the left-hand section of V8 and a sinusoidal oscillatory voltage appears across the tuned circuit, its duration dependent upon the capacitance C7. Movement of switch SW1 connects part of the resistor R19 to load the tuned circuit and produce an initial damping of the sinusoidal output. The duration of the damping depends upon the position of the switch. The sinusoidal output is fed to the grid of a limiting amplifier valve V9 which is normally biased beyond cut-off. The negative half-cycle output produced is fed to a secondary winding T3 of the line transformer T. Relay RL1 may be energized to operate contacts RL12 and RL11 to pass the output through T3 in the opposite direction. Mains power supply is connected across terminals N, L, and various tappings operate H.T. lines and heaters. The tested apparatus is connected between terminals R and N so that when it is switched on in one condition relay RL3 is energized closing its contacts RL31, RL32 to put condenser C7A in parallel with C7. In the apparatus's second position switch SW3 is also closed, by the control knob, to energize a relay RL2 and close its contacts, so putting condensers C7, C7A and C7B in parallel. Since the number of returned response pulses is directly dependent upon the capacitance in the C7 position different numbers of pulses are returned for different conditions of the set. Further information may be sent by delaying the respond pulses by a specific amount as described above. In a modification, Fig. 5, arrangement is made for N condensers to be put in parallel in the C7 position by pushing buttons, so increasing the amount of information which may be returned.