Super Systems 3L Series - Manual (Page 32)

Operations Manual Series 3L
32
9. Alarms
Alarms are used to alert an operator when a pre-set level has been exceeded. They are indicated by a scrolling
message on the display and the red ALM beacon. They may also switch an output – usually a relay (see section 7) to
allow external devices to be operated when an alarm occurs.
9.1 Types of Alarm
Up to six different alarms are available:-
1. Alarm 1 Configurable as any of:-
Full scale High
Hi – the alarm is triggered if the PV exceeds a maximum value
Full scale Low
Lo – the alarm is triggered if the PV exceeds a minimum value
Rising Rate of Change
r.roc - the alarm is triggered if the rate of increase in PV exceeds
the set level
Falling Rate of Change
F.roc. - the alarm is triggered if the rate of decrease in PV exceeds
the set level
2. Alarm 2
3. Alarm 3
4. Alarm 4
5. Sensor
Fault Alarm
The alarm is triggered if the sensor is open circuit
6. Power Fail An alarm is indicated after a power cycle. It is acknowledged and cancelled using ‘Ack’ buttons.
This may be useful to indicate that a power failure has occurred and the peak values will only
apply since return of the power.
Hysteresis is the difference between the point at which the alarm switches ‘ON’ and the point at which it
switches ‘OFF’. It is used to provide a definite indication of the alarm condition and to prevent alarm
relay chatter.
Latching Alarm is used to hold the alarm condition once an alarm has been detected. It may be configured as:-
none Non latching A non latching alarm will reset itself when the alarm condition is removed
Auto Automatic An auto latching alarm requires acknowledgement before it is reset. The
acknowledgement can occur BEFORE the condition causing the alarm is
removed.
Man Manual The alarm continues to be active until both the alarm condition is removed
AND the alarm is acknowledged. The acknowledgement can only occur
AFTER the condition causing the alarm is removed.
Evt Event ALM beacon does not light but an output associated with this parameter
will activate. An ‘Event’ is not acknowledged.
Blocking Alarms The alarm may be masked during start up of a process. Blocking prevents the alarm from being
activated until the process has first achieved a safe state. It is used to ignore start up conditions
which are not representative of running conditions.
A blocking alarm is re-initiated after a setpoint change.
See section 9.12 for an explanation of the behaviour of blocking alarms under different conditions.
Rising rate of
change
(units/minute)
An alarm will be
detected if the rate of
change in a positive
direction exceeds the
alarm threshold
Falling rate of
change
(units/minute)
An alarm will be
detected if the rate of
change in a negative
direction exceeds the
alarm threshold
Rate of change
< set rate
Negative rate of change in set in
engineering units per minute
Hysteresis
Alarm ON Alarm OFF
Rate of
change
> set rate
PV
Time
Alarm OFF
Time
Positive rate of change in set in
engineering units per minute Hysteresis
Alarm ON
Rate of change
< set rate
Rate of change
> set rate
PV