Patent GB-805799-A (GB)
Title: Improvements in or relating to apparatus for designating which of a plurality of signal input channels carries the signal of highest value of magnitude
IPC: G01R19/00
Filed: 1956-06-18
Abstract: 805,799. Electric tests. COMPANHIA PORTUGUESA RADIO MARCONI. June 18, 1956 [June 20, 1955], No. 18760/56. Class 37. An electronic switching circuit designating one of a plurality of signal input channels to indicate the channel carrying the highest signal amplitude by producing a trigger pulse on one of a plurality of output terminals respectively corresponding to the input channels, comprises an input stage for each channel converting a continuous input signal into a stepped waveform having successive constant values corresponding to instantaneous values of input at successive time intervals, and followed by a control thermionic tube having two control electrodes (to one of which the stepped signal is connected) operating in series, so that the tube conducts only when both electrodes are pulsed; a monostable pulse generator operated by the output of said tube, a delay network pulsed whenever the first of the two electrodes is pulsed to forward the pulse after a fixed delay to the first electrode of the control tube of the next sequential input channel, and for each channel a buffer tube whose control grid is connected to the second electrode of the corresponding control tube; the cathodes of all the buffer stages being connected to a positive bias source whose negative is returned to ground over a common cathode resistor, and the cathodes of all the control tubes being grounded over a second cathode resistor and the non-grounded terminal of the first cathode resistor, and the outputs of all the monostable pulse generators being differentiated and supplied to the cathodes of the control stages over a transformer having a balanced secondary; there being also provided a capacitor across the grid to ground circuit of a tube, whose cathode is connected to the ungrounded terminal of the first common cathode resistor, as a storage device, with the live side of such capacitance being connected respectively to the cathode and anode of charging and discharging tubes; together with a multivibrator generating a train of small pulses each of which once operates the charging tube whenever the tubes in the buffer stages draw plate current, and a second multivibrator producing a train of small pulses each of which actuates the discharging tube so long as the pulses in the primary winding of the differentiating transformer follow each other with a time delay exceeding a predetermined minimum time interval. Plural inputs of voltage signals C1, C2 ... Cn are connected over circuits converting each continuing input signal to a stepped waveform corresponding to the instantaneous value of the input during successive short intervals of time at a close predetermined constant level and stepping up or down as the input signal instantaneous value approaches in magnitude an adjacent level of a predetermined scale, and over optional D.C. amplifiers 13 to the negatively biased third grids of hexodes 1, 2 ... 3 whose first grids are respectively connected to negative bias through secondaries of transformers 38, 22, 30 and whose screens are respectively connected to a positive voltage through secondaries of transformers 16, 27, 33. Initially for low values of input voltage the hexodes are cut off, and operation of start switch 19 connects capacitance 20 in series with resistance 18 to the screens of hexode 1 to positively pulse the primary of transformer 16; the resultant secondary pulse being delayed in network 21 and energizing transformer 22 to positively pulse the first grid of hexode 2. The resultant positive pulse from the screen circuit thereof in the primary of transformer 27 is delayed in network 29 and energizes transformer 30 to positively pulse the first grid of hexode 3, whose resultant screen pulse in the primary of transformer 33 is delayed in circuit 37 and energizes transformer 38 to positively pulse the first grid of hexode 1, whose screen circuit develops a positive pulse to restart the cycle, which continues indefinitely; further similar hexode circuits being insertible in the chain through which the pulse circulates at a period which is the sum of the delay times of all the networks 21, 29, 37, &c. The arrival at the third grid of any hexode 1, 2 ... 3 of a voltage input step signal sufficient to drive the tube conductive causes anode current to flow during the cyclic positive pulsation of the first grid, and the resultant negative anode voltage pulse is resistance-coupled to an associated mono-stable multivibrator 4, 7: 5, 8 ... or 6, 9, whereby the second normally cut-off tube 7, 8 ... or 9 is driven conductive for a period time dependent on the time constant. A positive-voltage pulse is developed at the same time over the common cathode resistors 83, 84 of the hexodes and triodes 7, 8 ... 9, which cuts off all the hexodes and arrests the pulse circulation in the chain. A pulse is simultaneously generated at the anode of the first triode and capacitance coupled to the output D1, D2-or Dn to mark the channel to which the input signal is applied. On the multivibrator falling back into normal conduction of triode 4, 5 ... or 6; and cut-off of triode 7, 8 ... or 9, the cathode pulse collapses and a differentiating circuit 53, 54; 65, 66; ... or 78, 79 connected to the anode of triode 7, 8 ... or 9 generates a pulse which is amplified to energize the primary of transformer 22, 30 ... or 38 which positively pulses its associated hexode first grid to restart pulse circulation in the chain. The third grids of the hexodes are respectively connected to the grids of corresponding buffer triodes 85, 86, 87, biased from negative source 14, in combination with positive source 88 in series with resistor 84 also carrying the cathode current of the hexodes, the buffer triodes, and threshold control triode 105, so that no buffer triode conducts while the input step signal voltages are lower than a predetermined threshold value. Excess of an input over this value causes the appropriate buffer triode to conduct and the resultant voltage drop across common anode resistor 92, which reduces the grid voltage of D.C. amplifier triode 94 to drive positive the screen of tetrode 104 connected as a monostable multivibrator with triode 125. The tetrode conducts and triode 125 is cut off for a period determined by the time constant to positively pulse the grid of triode 126, which admits a current pulse to charge capacitance 120 from positive source 119 whereby triode 105 is biased positively so that its anode current raises the cathode voltage across resistor 84, in a series of steps so that the threshold value for conduction of any buffer triode is raised to a level at which it exceeds the step input signal and the hexode chain continues to pulse. Excess of any input step voltage over the threshold value operates the appropriate hexode chain multivibrator, which generates a cathode current pulse in the primary of transformer 82, and a differentiated secondary pulse is applied to the grid of normally conducting triode 102 connected as a bistable multivibrator with normally cut-off triode 123, so that the leading edge of the pulse drives the latter conducting and the former to cut off, while the trailing edge of the differentiated pulse over capacitance 133 momentarily drives triode 138 conducting, whereby capacitance 116 shunting cathode resistor 115 of triode 102 is discharged to restore the multivibrator to the state in which triode 102 conducts and triode 123 is blocked. Capacitance 116 is then recharged over triode 102 and resistor 108 to a positive value such that after a time equal to that for the circulation of one pulse through the hexode chain it drives triode 134 conducting against a bias preset by resistors 135, 136. Occurrence of a further pulse from transformer 82 prior to this instant discharges capacitance 116 over triode 138 so that triode 134 remains cut off, while non-occurrence of such a pulse allows triode 134 to open and the bistable multivibrator comprising pentode 148 and triode 154 to generate pulses, so that the anode pulses from triode 154 drive triode 139 conducting to pulsatingly discharge capacitance 120 step-by-step until the input step voltage exceeds the threshold predetermined by the voltage thereon; when a pulse from transformer 82 discharges capacitance 116 as above, the pulse circulation in the hexode chain is arrested and the output channel corresponding to the input receiving the greatest input amplitude receives a marking pulse as above, until the signal at another input channel exceeds the threshold set by the first input. The input signals may themselves be varied by discrete quanta corresponding to the amplitudes of the steps by which the operative threshold is varied, and may represent physical variables. The output trigger pulse corresponding to the greatest input may be arranged to suppress the operation of the hexode corresponding thereto, so that the apparatus operates to indicate the input channel receiving the next highest signal. Specification 694,9.51, [Group XL (c)], is referred to.