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D-5000 / May 2000
METERBRIDGE and CLOCK
Console Clock
The Wheatstone digital clock is a six-digit time-of-day clock with LED
display. The clock is designed with CMOS circuits and an on-board crystal-
controlled time base oscillator. There are two basic parts to the clock: a main
PCB containing the clock circuits and clock set controls (also may include
capacitor backup) and a second PCB containing displays. Clock set controls
may be accessed by removing the meterbridge cover.
Controls
The clock is controlled by a trimmer and two switches; the trimmer and
switches are mounted on the main clock PCB assembly.
The trimmer alters the frequency of the quartz-controlled oscillator,
which in turn causes the clock to run slightly slower or faster. In order to keep
accurate time, the oscillator must run at 4.096 MHz. The oscillator is set to this
frequency at the factory. However, due to the nature of quartz/crystal-
controlled oscillators, there may be a slight change in the frequency of the
oscillator during the first few months of operation due to the aging effect of
quartz crystals. A minor readjustment of the trimmer will compensate for this
effect.
A divided by 4 buffered output of the oscillator is available at pin #7 of IC #U1
to assist in adjusting the oscillator.
Setting the Time
The setting controls consists of two switches: MODE and SET. To set the
clock, open the meterbridge cover and stand behind the console:
1) The control switches (mounted inside the meterbridge bottom) are la-
belled "M" and "S". "M" (
Mode) is used to scroll from seconds to min-
utes to hours; "S" is used to
Set the time. The procedure is to set the clock
slightly ahead of the current time, hold the second count at "00" until the
current time catches up, and then release the count.
2) Press the MODE button until the hour digits blink. Depress the SET
button until the desired hour is displayed.
3) Press the MODE button until the minute digits blink. Depress the SET
button until the desired minute count is displayed.
4) Press the MODE button until the second digits blink. Depress and hold
the SET button; the seconds display will hold at "00". When the current
time catches up to the display, release the SET button. The clock will
start counting. Hit the MODE button three more times to place the clock
into working mode.
Capacitor Backup
With the meterbridge open note the super capacitor at C25. This super
capacitor is self charging. Note that the super capacitor does NOT light up the
clock display; it powers the clock crystal to keep it from losing count ( it will
do this about one hour).
D-5000 / Mar 2001
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