3200 Series
Part No HA028651 Issue 7.0 Apr-09 61
Hysteresis 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 is used to maintain 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.
Latching
Alarm
Evt
Event
ALM beacon does not light but an output associated with this parameter will
activate. A scrolling message may be configured using iTools, as described in
section 17.7. If a message has been configured it will scroll across the display
while the event is true.
Blocking
Alarms
The alarm may be masked during start up. 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 12.2 for an explanation of the behaviour of blocking alarms under different conditions.
From firmware version 2.11, two rate of
change alarms are available. These are:-
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
Alarm OFF
Time
Positive rate of change in set
in engineering units per
Hysteresis
Alarm ON
Rate of change
< set rate
Rate of change
> set rate
PV
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