Patent GB-1028534-A (GB)
Title: Improvements in electrical circuitry
IPC: G01R13/30
Filed: 1963-04-30
Abstract: 1,028,534. Electric selective signalling systems. TEKTRONIX Inc. April 30, 1963 [June 15, 1962], No. 17049/63. Heading G4H. A system for measuring a characteristic relating either to one or to two electrical waveforms comprises means for locating a lower limit marker and an upper limit marker on the waveforms (either both on one waveform or one on each waveform), means for producing from the marked portions of the waveforms a lower limit signal and an upper limit signal, and means for generating a number of pulses significant either of the difference between the amplitudes of the lower limit and the upper limit signals or of the period of time between the instant when the waveform carrying the lower marker passes through an amplitude equal to a first selected function of the lower limit signal and the instant when the waveform carrying the upper marker passes through an amplitude equal to a second selected function of the upper limit signal. As described, two waveforms A and B are displayed on an oscilloscope C.R.T., Fig. 1. Each waveform carries a first marker 36, 38 which occurs at the beginning of the horizontal sweep (see also Figs. 5A, 5B) and which is referred to as a " 0% " marker, and a variable marker 32, 34 referred to as a " 100% " marker since in operation this marker is normally manually adjusted, 26, 28, to lie, as shown, on the peak of its waveform. Each waveform is sampled at the marked points, the resulting amplitudes being stored in memories 42, 46, 48, 54, and the 0% and 100% levels are applied to opposite ends of a pair of tapped potentiometers 43, 44 and 50, 52. The tapping points correspond to the marked percentage levels, 10%, 20%, 27% &c., and the movable taps are shown in the 10% and 90% positions. The tapped outputs from these potentiometers, the 0% and 100% levels and also the actual A and B signals themselves are fed to two switches 56 and 58, each having two ganged wipers. In the positions shown switch 56 connects the 10% tap from potentiometer 44 and the A signal to a start comparator and switch 58 connects the 90% tap from potentiometer 43 and the A signal to a stop comparator. Now the 10% and 90% levels are static but the A signal varies in the manner shown on the C.R.T. Thus when the A signal reaches the 10% level the start comparator produces an output which, via a start multivibrator 80, opens a counting gate 88 and when the A signal rises sufficiently to reach the 90% level the stop comparator produces an output which closes gate 88. - Also for the duration that gate 88 is open clock pulses from a pulse generator 74 pass to a counter 90. Thus the count reached represents the time taken for waveform A to rise from the 10% to the 100% level, and for the convenience of the operator this period is also brightened on the C.R.T. at 92. The two comparators each have " slope" switches whereby they can be set so as to respond only to the first or second positive or negative slope of the varying input waveform. Thus with a different setting of the control switches it is possible to measure the width of a pulse from, say, the 20% level on the first positive slope to the 20% level on the first negative slope or the cyclic period (and hence the frequency) of a signal can be measured from, say, the 50% level on the first positive slope to the 50% level on the second positive slope. It is also possible to measure the period between a point on waveform A and a point on waveform B. It is also possible to measure the difference between the 0% and the 100% levels (that is the amplitude) of waveform A (or B) by setting switches 56 and 58 so that the 0% and the 100% levels of waveform A are compared with a voltmeter ramp (V - MR) signal, and by setting a switch 78 so that voltmeter clock pulses are counted instead of sampling pulses. The counting gate 88 is overridingly controlled by a display time multivibrator so that each count is displayed long enough for it to be read before a new count is made. Detailed gating, storing and comparing circuits are described using conventional thermionic and semi-conductor techniques.