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Fail Safe Alarm Feature
The controller is equipped with the Fail Safe alarm feature to protect the process against critical errors
arising from power interruptions, power surges and human errors.
The Fail Safe alarm feature resolves these predicaments on two fronts: hardware and software.
Hardware
To eliminate problems of blackout and line failure, the alarm function operates in a "Normally Closed"
state and hence the alarm is triggered if the limits set are exceeded or when the power is down.
This is an important feature since with most controllers the alarm terminals close only when an
abnormal situation arises; however, due to line interruption, no alarm condition
Software
Software is employed to set off the alarm in abnormal circumstances, e.g. if the control-dosing relay
is On for too long a period.
In both cases, the Alarm LED will also provide a visual warning signal.
To enter in Fail Safe mode:
• connect the external alarm circuit between the FS•C (Normally Open) and COM terminals
• an alarm will warn the user when the pH goes over the alarm thresholds, the power breaks down,
and in case of a broken wire between the controller and the external alarm circuit.
Figure 19:
Note In order to have the Fail Safe feature activated, an external power supply has to be
connected to the alarm device.
8.3.3. Connecting the Power Supply
Qualified personnel should perform wiring only. The personnel must have read and
understood the instructions in this manual when making power connection.
• Run the power cable through the power cable gland
power connector from the power board.
• Using a screwdriver, connect the cable leads to the jack power connector.
Note: each leads location is marked on the power supply board.
• Insert the power connector in the power socket. See
NC
NO
COM
Connecting Alarm Circuit Between FS•C & COM Terminals
(Figure
15, label 5). Remove the removable
Figure 17.
Replace safety cover over terminal 2.
occurs.
31
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