WHARTON MASTER/SLAVE/INDEPENDENT CLOCKS
A master/slave clock system manufactured in the UK by Wharton Electronics, using
its own time code system to drive the slaves, a code capable of being sent long
distances over standard unscreened two-core wiring. Clock displays operate as
slaves or in stand-alone mode.
The 400A series of clocks, calendar clocks and world time-zone display systems
provide a precise and elegant display of time, or time and date, using bright and clear
red or green LED characters with both manual and automatic brightness control.
400A series clocks are normally powered from a mains supply, an automatically
recharging internal battery provides a standby supply to maintain the time keeping in
the event of an interruption in the mains power supply. Low voltage operation is
available as an extra cost option.
All may be used either as stand-alone units, operating from their internal high stability
quartz crystal oscillator or as slave clocks controlled by one of a variety of signal
sources. Additionally, the 401A, 420A and 490A series clocks may be used as
stopwatches or elapsed time counters when controlled by a type 402A or 496A
external switch unit. The 402A switch control unit enables both up and down counting
from a pre-programmed start time with a wide range of programmable display freeze
and counting modes with an optional relay closure when the count reaches zero.
The 400A range are supplied in rectangular cases suitable for surface mounting on a
wall, flush mounting in a panel or with a mounting box for installation in a solid wall.
Ceiling suspension of single and double sided units is available.
Some of the more popular types are held as stock items, but others are available to
special order, on short lead time. Special application versions are not listed below but
details are available on request. Clocks may be supplied with different case colours
and finishes to special order. Special outer cases, providing protection to IP65, can be
supplied for use in difficult environmental conditions. The various display formats are
available in a wide variety of sizes with character heights from 14mm to 200mm and
suitable for use at maximum viewing distances from 14 to 120 metres.
Master Clocks
All 400 series clocks and calendar clocks may be used either as independent units,
maintaining timekeeping from their internal high stability quartz crystal oscillator or as
slave displays with time-keeping derived from an external master clock. Two types of
master clock may be used. The first is an impulse master clock, normally used for
controlling analogue slave clocks. The impulse master clock provides control by
means of impulses every second, half minute or minute. The principal disadvantage of
this type of control is that each slave clock requires accurate initial time setting and will
display an incorrect time for up to one hour during seasonal time changes.
Alternatively, a 4850 digital master clock may be used, which produces a low voltage
digital time and date serial code (called W482) which will directly control up to 50 slave
displays. The W482 time code output is intended to control 400A series displays and
clocks operating in slave mode and displaying time, or time and date, in up to fifteen
different time-zones and can be pre-set to provide an automatic seasonal time
change with different dates and time for each of the fifteen time zones. This code is a
low voltage (12V nominal), 50 bits per second digital time and date signal that has
almost total immunity to external electrical noise. Digital clocks and displays may be
driven at distances of up to 1km using a non-critical, unscreened, single cable pair
transmission link. It should not be confused with SMPTE/EBU time code - they are
completely different types of code.
All time setting is carried out centrally at the master clock; an additional slave display
will automatically show the correct time within one minute of being connected to the
system. Following a power failure all slave displays will show the correct time within
one minute. Time and date code is not transmitted during power failures as the slave
clocks are automatically corrected when power returns.
The 1U 19-inch rackmount, 4850 master clock provides the proprietary W482 code,
as well as RS232, RS422 and RS485 outputs, programmable relay contacts and an
RS232 “on-time” signal as standard and can be optionally supplied with EBU/SMPTE
timecode, to allow communications with computers and broadcasting equipment.
Free software is provided for use on Windows NT4 (x86) and Windows 95/98
platforms for synchronisation purposes.
Serial time and date information can be supplied in ASCII format to RS232, RS422
and RS485 standards, which can transmit in one of more that twenty different serial
ASCII time and date telegrams at user selected intervals. General purpose formats are
user configurable for 7 or 8 data bits, odd, even or no parity, a baud rate of 1200,
2400, 4800 or 9600 and message repetition rates of every second, minute, five
minutes, hour, day or on request. A single pulse per second, “on-time” signal output is
also available to RS232 precision.
Relay changeover contacts can be programmed to show a changeover for one
second every 5 seconds, one minute, hour or once per day at a programmable time.
They can also be used to changeover in the event of a power failure, an error state or
when locked to an external time reference. The conacts are rated at 30V DC @
500mA.
The standard internal high stability quartz oscillator has an accuracy of ± 0.1 seconds
per day at 20-25°C. If synchronised with the 488GPSB receiver system (available
seperately), the RS232 “on-time” pulse per second is maintained to within 50
microseconds. Optionally, this can be connected to a 484 series radio time-code
receiver to enable the internal time-base to be synchronised with the signals trans-
mitted from MSF (Cumbria, UK - formerly from Rugby, UK) or DCF (Mainflingen, West
Germany). When synchronised to either signal the master clock time will typically be
correct to within 30 mS of UTC (Universal Time Code).
. . . continued overleaf
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