Watlow 8LS Controller - Manual (Page 76)

68 8LS User’s Guide
Setup
Alarm Types
Global Alarms
Global alarms occur when a loop alarm, set to Alarm, is
unacknowledged, or when there are any unacknowledged failed sensor
alarms. (If an alarm occurs, the 8LS front panel displays an appropriate
alarm code). Even if the alarm condition goes away, the global alarm
stays on until you use the Alarm Ack key (or ANASOFT) to
acknowledge it.
Process Alarms
Process alarms include high and low deviation and high and low process
alarms. You can set each of these alarms to Off (no alarm function) or
On (Standard alarm function).
• High process and high deviation alarms activate when the process
variable goes above a value you set. They remain active until the
process variable goes below that value minus the deadband. (See
diagram below.)
• If you don’t use a digital output for PID control, you can assign it to
one or more process variable alarms. The output is active if any of
its alarms are active. All alarm outputs are active Low or active
High, depending on the global alarm output polarity setting.
• Low process and low deviation alarms activate when the process
variable goes below a value you set. They remain active until the
process variable goes above that value plus the deadband. (The dia-
gram below shows these alarms.)
When the controller powers up or the setpoint changes, deviation alarms
do not activate until the process goes inside the deviation alarm band--
preventing deviation alarms during a cold start. (High and low process
alarms are always enabled.)
High Alarm Limit
Setpoint
Low Alarm Limit
SP + Deviation
SP - Deviation
} Deadband
} Deadband
} Deadband
} Deadband
High deviation alarm on
High deviation alarm off
Low deviation alarm on
Low deviation alarm off
High process alarm off
High process alarm on
Low process alarm on
Low process alarm off