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In addition to the user-selectable alarm relays, all pH500
and mV600 models are equipped with the
Fail Safe
alarm
feature.
The
Fail Safe
feature protects the process against critical
errors arising from power interruptions, surges and human
errors. This sophisticated yet easy-to-use system resolves
these predicaments on two fronts: hardware and software.
To eliminate problems of blackout and line failure, the alarm
function operates in a “Normally Closed” state and hence
alarm is triggered if the wires are tripped, or when the power
is down. This is an important feature since with most meters
the alarm terminals close only when an abnormal situation
arises, however, due to line interruption, no alarm is sound-
ed, causing extensive damage. On the
other hand, software is employed to set
off the alarm in abnormal circumstanc-
es, for example, if the dosing terminals
are closed for too long a period. In both
cases, the red LED’s will also provide a
visual warning signal.
The Fail Safe mode is accomplished
by connecting the external alarm circuit between the FS•C
(Normally Open) and the COM terminals. This way, an alarm
will warn the user when pH goes over the alarm thresholds,
the power breaks down and in case of a broken wire between
the process meter and the external alarm circuit.
Note
In order to have the Fail Safe feature activated, an external
power supply has to be connected to the alarm device.
