IM 12D7B2-E-H
15
1. What is HOLD?
HOLD is a function freezing the output sig-
nal temporary, during normal maintenance,
preventing 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 can
only be used when a recorder is connec-
ted.
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 Conductivity-control sys-
tems.
2. How does it work?
The HOLD-function has to be activated from
the *-menu before it can be used.
The EXA SC200 will keep the output frozen
during the following events:
- Access to the *-menu.
- Access to the calibration mode.
- Switching it from the MODE-menu.
HOLD is signalled in the display by a special
field.
The operator is prompted to switch HOLD
on or off before returning to normal mea-
surement.
3. Example
In a storage tank the concentration of sodi-
um hydroxide (caustic soda) has to be kept
at 5% . The mixing process is controlled by
a conductivity transmitter and electro-mag-
netic valves.
During maintenance of the conductivity cell
or the transmitter the HOLD function is acti-
vated to keep the mixing process from was-
ting precious chemicals to the sewer.
The HOLD function is set for a fixed output
so that the dosing valves will not be activa-
ted.
4. Time out
Hold will be de-activated after 20 minutes if
no key is pressed. To cancel this function
see 7-8.
4-3. Set up HOLD function
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