Patent GB-620393-A (GB)
Title: Improvements in or relating to electrical time measurement
IPC: G04F10/10
Filed: 1945-12-04
Abstract: 620,393. Measuring short-time intervals. STANDARD TELEPHONES & CABLES, Ltd., and CHILDS, P. A. Dec. 4, 1945, No. 32733. [Class 37] [Also in Group XXXVIII] A time interval measuring device comprises separate electrical " start " and " end " signal responsive means having substantially identical delay characteristics, a timing condenser adapted to be charged by a voltage established in response to the start signal, means responsive to the end signal for establishing a voltage in opposition to the charging voltage for terminating said charge, and means for holding the condenser charge sufficiently long to operate a visual device indicating the charge and hence the time interval between the signals. The interval to be measured is defined by " start and "end" pulses applied through respective transformers T1, T2, Fig. 1, to fire thyratrons V1, V4. Immediately V1 fires, the potential drop established across its cathode resistor R1 commences to charge the timing condenser C over the series connected resistances R2, R3 and diode rectifier V3. When V4 fires, the consequential potential drop across its cathode resistor R3 drives the cathode of V3 positive relative to its anode so stopping further charging of condenser C which retains a charge proportional to the interval being measured. The grid potential of a triode V2 follows that of condenser C and is indicated on a voltmeter M which may be calibrated to read time direct. The meter M, which with the valve V2 forms a known type of valve voltmeter having negative feedback to reduce errors due to variations in valve characteristics, is zeroized by (1) operating a start switch to apply H.T. to the valve anodes at S2, and at S1, remove the shortcircuit across condenser C, (ii) applying zero voltage to the cathodes of V1, V4, and (iii) adjusting potentiometer R1 until meter M reads zero. Full scale is then set by applying the charging voltage for the appropriate time and adjusting R6 to full scale reading. In a modification, Fig. 2, the firing of thyratron V4 by the " end " pulse cancels out the charging potential by applying a negative potential to a tapping on the time base resistance R2, R3. In this case charging of the measuring condenser C during the measuring interval swings the grid of the voltmeter valve V2 more positive in contradistinction to the Fig. 1 arrangement. In another arrangement, Fig. 3, for measurements of the order of micro-seconds, the potential across the time-base condenser C1 is not measured directly but is used to charge a further condenser C2. Operation is similar to that of Fig. 1 except that when the cathode of V2 follows. the negative swing of the grid it charges C2 through the diode portion of V2. For very short intervals the charge on C1 may leak away rapidly, but C2 remains charged and its potential is measured as before by means of a further valve V5 and meter M. In a further embodiment, Fig. 4 (not shown), the direct reading meter M of Fig. 1 is replaced by a calibrated potentiometer and magic-eye-type indicator associated with V2, the potentiometer being adjusted, after a measurement, until the fluorescent target diagram just closes, the time interval being then indicated on the potentiometer scale. Fig. 5 shows the arrangement of Fig. 1 in detail, and includes a stabilizer V5 for the anode supply which may be A.C. or D.C., a multiple pole switch CS 1 ... CS4 having three positions corresponding to check zero, check full scale, and operate conditions, and two-pole, six-way switches SSS, ESS for selecting appropriate tappings on the pulse transformers T1, T2 and corresponding D.C. limiting resistances R7 ... R12, R27 ... R32. Various circuit connections are brought out to octal valve sockets SJ, EJ. A pair of test leads may then be connected to an 8-pin plug having internal strappings for the setting up of various desired circuit functions. These connections are such that when the " start " and " end " signals are of small amplitude an amplifying valve may be inserted in the socket and function to supply amplified signals to the pulse transformers. The time-base consists of a resistance R14 which by means of a selector switch RS may be series connected with one or more of resistances R18 ... R24 and the measuring condenser C4. Figs. 6-8 (not shown) illustrate elementary ways of deriving " start " and " end " pulses corresponding, for example, to the operate time of a relay contact and Fig. 9 (not shown) to the interval between a light flash and the time of reception of the sound of the explosion producing it. Specification 620,394 is referred to.