Patent GB-1225657-A (GB)
IPC: G04F10/04
Filed: 1968-06-26
Abstract: 1,225,657. Measuring short time intervals. ELECTRICITY COUNCIL and P.N. NIELD. July 18, 1968 [June 26, 1968], No. 30487/68. Heading G1U. [Also in Division H3] To measure the time interval between two events occurring at separate locations, each of which is connected by a signal transmission path to a receiving station, pulses A1, A2, corresponding to the events, are transmitted to the receiving station, whilst further pulses, Figs. 2c -f, are transmitted from the receiving station to each of the locations and back again to provide a measure of the difference in the transmission times along the two paths and thus enable the time interval between pulses A1, A2 as received to be corrected for this difference to provide a true indication of the time interval t 1 . General system Figs. 2a-2g Pulses A1 A2 corresponding to the two events are each transmitted to the receiving station, where they are received as pulses A1<SP>1</SP>, A2<SP>1</SP> with a delay between them comprising the original delay t plus the difference t 2  in transmissions times. Pulses B1, B2 are sent from the receiving station to each location, where they are received as B1<SP>1</SP>, B2<SP>1</SP> and applied to delay circuits such that, after a fixed delay, pulses C1, C2 are sent back to the receiving station, the delay being just sufficient to allow the transmission lines time to discharge. The received pulses C1<SP>1</SP>, C2<SP>1</SP> have a delay between them equal to 2 t 2 , which may be combined with the delay t 1  + t 2  between A<SP>1</SP>, A<SP>2</SP> to provide a measure of t 1 . If the events occur repetitively, with the same time interval between them, the sequence of pulses shown in Fig. 2 is repetitively produced and so a true indication of t 1  may be provided by supplying to a D.C. meter a signal, Fig. 2g, comprising positive pulses P1 of amplitude I in the intervals A1<SP>1</SP>-A2<SP>1</SP> and negative pulses P2 of amplitude ¢I in the intervals C1<SP>1</SP> -C2<SP>1</SP>, this signal thus having an average value proportional to t 1 . In a modification pulses P 2  may have an amplitude I but be produced in alternate cycles only. Compensation may also be made for differences in the delay times of the delay circuits at the two locations. In one such arrangement the pulses A1, A2 are arranged to be delayed once by these circuits whilst C1, C2 are delayed by twice the delay time of these circuits. In another arrangement pulses C1, C2 only suffer a single delay, but further pulses are also sent to each location, delayed twice in the delay circuits and then sent back. giving a third pulse P3 which in combination with P1, P2 provides the required measure of t 1 . Circuit Details The circuitry at the receiving station is shown in Fig.3, all mono- and bi-stables being shown in their quiescent states. Pulses A1<SP>1</SP>, A2<SP>1</SP> from the two locations are received at transformers 13a, 14a respectively. If transformer 13a receives its pulse first, gate G1A is opened to trigger monostable M4 and current generator I2, the latter thus supplying current (corresponding to pulse P 1) to averaging meter IM. When transformer 14a receives its pulse, gate G 1  B will be opened to set bi-stable B22, thus blocking gate G5 to terminate the current pulse P1. If transformer 14a had received its pulse first a pulse P 1 of opposite sense would have been generated by generator I 1 . Monostable M4 also controls the generation, by monostables M1, M2, of the pulses B1 B2 which are sent down the transmission lines via transformers 30, 31. At the same time monostable M1 disables gates G1A, G1B and enables gates G2A, G2B, so that when pulses C1<SP>1</SP>, C2<SP>1</SP> are received back they open the latter two gates to cause generation of the pulse F 2 in a similar way. In Fig. 3 the pulse F2 is generated by one of the two further generators 13, 14, but if pulses B1, B2 are only being sent out in alternate cycles, Fig.3a (not shown) generators I1, I2 may be used for this purpose since the pulses P 1, P2 then have the same amplitude. The circuitry at each of the two locations, Fig. 4 (not shown) comprises a threshold circuit (AC1) which, on receipt of pulse B1<SP>1</SP> or B2<SP>1</SP> sets a bi-stable (SB1) and triggers a delay circuit in the form of a crystal oscillator-supplied counter (43). When the counter reaches its limit the bi-stable is reset to cause the generation of the pulse C1 or C2. The use of a counter for the delay circuit may be avoided if compensation is being made for differences in the delay circuits of the two locations, the counter being replaced by two cascaded monostables.