29 Installation & Controller Start-Up
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 occurs.
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 provides a visual warning.
Connect the external alarm circuit between the FS•C (Normally Open) and COM terminals to enter in Fail Safe
mode.
Note: An alarm warns the user when the measured parameter exceeds the alarm thresholds; the power breaks
down in case of a broken wire between the controller and the external alarm circuit.
NO
NC
COM
Figure 20: Connecting Alarm Circuit Between FS•C & COM Terminals
Note: In order to have the Fail Safe feature activated, an external power supply has to be connected to the
alarm device.
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 (Figure 14, label 5).
• Remove the power connector from the power board.
• Use a screwdriver to 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 Figure 18. Replace safety cover over terminal 2.
To Next Page
Loading...
