D8 Series User’s Guide
Chapter 4: Operation and Setup
75
The RTD alarms are enabled on any loop with Input Type set to RTD.
Restore Automatic Control After a Sensor Failure
This feature returns a loop to automatic control after a failed sensor is repaired. To enable this
feature:
• Choose a digital input for the
RestoreAuto
parameter in the
Control
menu.
• Connect the digital input to the dc common terminal on the controller.
Process Alarms
The D8 has four process alarms, each of which you can configure separately for each loop:
• Alarm low
• Alarm high
• Low deviation alarm
• High deviation alarm
What Happens if a Process Alarm Occurs?
If a process alarm occurs, the controller does the following:
• Shows an alarm code on the display. Alarm Displays on page 63
• Activates the global alarm output. Global Alarm on page 76
• Activates the digital output that is assigned to the process alarm (if applicable). The digital
output remains active until the process variable returns within the corresponding limit and
hysteresis. The alarm output deactivates when the process returns to normal.
Process Alarm Outputs
Any digital output that is not used as a control output can be assigned to one or more process
alarms.
The controller activates the output if any alarm assigned to the output is active. Process alarm
outputs are non-latching—that is, the output is deactivated when the process returns to normal,
whether or not the alarm has been acknowledged.
Specify the active state of process alarm outputs at the
D/O alarm polarity
setting in the
Global
setup
menu.
Alarm Function: Standard Alarm or Boost Output
You can configure each process alarm as either a standard alarm or a boost alarm:
• A standard alarm provides traditional alarm functionality: The operator must acknowledge the
alarm message on the controller display, a latching global alarm is activated, and the alarm
can activate a user-specified nonlatching alarm output.
• A boost alarm provides on/off control output using the alarm set points. For example, you
could configure a high deviation alarm to turn on a fan. The alarm activates a user-specified
non-latching output. Alarm messages do not have to be acknowledged, and the global alarm
is not activated.