24
FS•O = NC (Normally Closed)
De-energized Relay
COM
FS•C = NO (Normally Open)
Energized Relay
ALARM RELAY
The alarm relay functions in the following manner:
During alarm condition, the relay is de-energized. When not
in alarm condition, the relay is energized.
Example: High alarm set at 1400 µ S
Low alarm set at 600 µS
An hysteresis will eliminate the possibility of continuous se-
quences ‘energizing/de-energizing’ of the alarm relay when
the measured value is close to the alarm setpoint. The alarm
hysteresis amplitude is 1.5% of full scale.
Moreover the alarm signal is generated only after a user se-
lectable time period (alarm mask) has elapsed since the
controlled value has overtaken one alarm threshold. This
additional feature will avoid fake or temporary alarm condi-
tions.
Note If the power supply is interrupted, the relay is de-energized as
if in alarm condition to alert the operator.
In addition to the user-selectable alarm relays, all EC/TDS
controllers 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 elimi-
nate 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.
