Horology: time measuring systems or devices – Electrical time base – Solid state oscillating circuit type
Patent
1991-06-18
1993-04-20
Miska, Vit W.
Horology: time measuring systems or devices
Electrical time base
Solid state oscillating circuit type
368201, 331 1R, G04F 500, G04B 1800
Patent
active
052048454
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of and apparatus for adjusting the pulse rate of a local clock to a desired pulse rate. The invention is particularly though not exclusively useful in an arrangement where the clock is incorporated in a remote station associated with a central control station such as, for example, an energy management system, and must be locked into the time of day within a set tolerance and where any clock synchronizing pulse transmitted from the control station to synchronize the local is subjected to random delays in the control station or the transmission medium.
BACKGROUND ART
In a known energy management system used to record consumption of electricity at consumers' premises, electronic registers are used to record the amount of electricity consumed during a number of different tariff rate periods per day. Thus there may be a high tariff rate register, a medium tariff rate register and a low tariff rate register and a time of day clock determines whether consumption occurs during a peak period, a normal period or a low cost period so the meter registrations are recorded in the appropriate register. It is thus necessary for the time of day clocks at each consumer's meter to be accurately locked into the time of day within a set tolerance of e.g. one minute.
In a system where a central computer can monitor the meters at each consumer's premises over the consumer's line, a time signal may be transmitted from the central computer at regular intervals, e.g. once a day. However, the transmission process has an inherent random delay while accessing the subscribers' energy management terminals (EMT). This delay may be of the order of 30 seconds between when the central computer transmits the time signal and when it is received by the EMTs.
There will thus usually be a difference between the time registered by the EMT's time of day clock and the clock synchronizing signal received from the central computer due to drift in the EMT clock and due to the random transmission delay. Both the drift and the delay are unknown parameters but a maximum drift will usually be specied in the tolerances for the EMT. This may be, e.g. 0.04 s per 15 minutes (40 per day).
A further complication may be added if the requirements of the electricity supply authority require that the time intervals for the consumption periods be within a given tolerance. In the US the electricity metering standard ANSI C12.13 requires an accuracy of 15 minutes.+-.0.9 seconds.
This latter requirement means that the EMT clock cannot automatically be reset in synchronism with the received clock synchronization signal because such a time step may exceed the permissible tolerance.
It is an object of the present invention to provide a method of and an apparatus for adjusting the pulse rate of a local clock to obtain a more accurate time signal therefrom in the absence of an accurate clock synchronization signal.
It is a further object of the present invention to provide a method of and an apparatus for adjusting the pulse rate of a local clock to obtain a more accurate time signal therefrom when using a clock synchronization signal for synchronizing said local clock transmitted from a remote station via a communication link which introduces random delays to the transmission of the synchronization signal.
SUMMARY OF THE INVENTION
According to the invention in its broadest form there is provided a method of adjusting the pulse rate of a local clock, said method comprising the steps of generating a first pulse train at a first predetermined rate, dividing said first pulse train by a selectable divisor to produce a second pulse train, the value of said divisor being selected so that the rate of the said second pulse train is varied within a predetermined range.
According to a further aspect of the present invention there is provided a method of synchronizing a local clock means having a plurality of selectable pulse rates, said method comprising the steps of measuring the time difference between the local clock means
REFERENCES:
patent: 3914706 (1975-10-01), Hammer et al.
patent: 4154053 (1979-05-01), Chetelat et al.
patent: 4187518 (1980-02-01), Martin et al.
patent: 4456386 (1984-06-01), Deliea
patent: 4707145 (1987-11-01), Ishida
ANSI Standard C12 & 13, "Time-of-Use Registers for Electromechanical Watthour Meters", IEEE Nat'l. Bureau of Standard, 1985, pp. 7-16.
Jeremy Peter G.
Stanbury Evan J.
ALCATEL N.V.
Miska Vit W.
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