IM 12B6C2-E-H
1. What is HOLD?
HOLD is a function freezing the output signal
temporary, during normal maintenance, pre-
venting all sorts of alarming situations to
occur.
Two possibilities are generally used:
a. Keeping the output at the LAST value
just before the start of maintenance. This
should be used when recording and not
controlling instruments are connected to
the output signal.
b. Keep the output at a preset FIXED value
which will not cause any of the alarms to
go off or any controlling action to be
taken. This is the preferred situation
when dealing with pH-control systems.
2. How does it work?
The HOLD-function has to be activated from
the commissioning menu before it can be
used.
The EXA PH200 will keep the output frozen
during the following events:
a. Access to the commissioning menu.
b. Access to either of the calibration modes.
c. Switching it from the maintenance menu.
HOLD is signalled in the display by a special
flag.
The operator is prompted to switch HOLD
on or off before returning to nor mal mea-
surement.
3. Example
In a neutralization set-up with both acid and
base dosing systems the neutral value is pH
7.00.
Activate the HOLD function and choose the
FlXed output value.
The span was set for 2-12 pH (see §4-2).
Thus pH 7.00 = 12 mA. Adjust the preset
value for the output at 12 mA.
During maintenance the output will be at 12
mA = pH 7.00 and no acid or base will be
pumped.
4. Auto return
Hold can be de-activated after 10 minutes if
no key is pressed. To cancel this function
(see §7-9).
15
4-3. Set up the HOLD-function
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