D8 Series User’s Guide
Chapter 7: Troubleshooting and Reconfiguring
137
Process Alarms
When a process alarm occurs, the controller switches to the single-loop display for the loop with the
alarm and displays the alarm code (see Alarm Displays on page 63).
Possible Causes of a Process Alarm
In a heating application, a low alarm or low deviation alarm may indicate one of the following:
• The heater has not had time to raise the temperature.
• The load has increased and the temperature has fallen.
• The control mode is set to manual instead of automatic.
• The heaters are not working because of a hardware failure.
• The sensor is not placed correctly and is not measuring the load’s temperature.
• The alarm settings are too tight. The process variable varies by more than the alarm limits
because of load changes, lag or other system conditions.
• The system is so poorly tuned that the temperature is cycling about set point by more than
the alarm set point.
NOTE!
In cooling applications, similar issues cause high alarms.
In a heating application, a high alarm or high deviation alarm may indicate one of the following:
• The process set point and high alarm set point have been lowered and the system has not
had time to cool to within the new alarm setting.
• The controller is in manual mode and the heat output is greater than 0 percent.
• The load has decreased such that the temperature has risen.
• The heater is full-on because of a hardware failure.
• The system is so poorly tuned that the temperature is cycling about set point by more than
the alarm set point.
NOTE!
In cooling applications, similar issues cause high alarms.
Responding to a Process Alarm
Your response to an alarm depends upon the alarm function setting, as explained in Table 7.1.
Table 7.1
– Operator Response to Process Alarms
ALARM FUNCTION
OPERATOR RESPONSE
Boost
The operator does not need to acknowledge the alarm. The alarm clears
automatically when the process variable returns within limits.
Standard
Acknowledge the alarm by pressing
x
on the keypad or via communications.
The alarm clears after the operator acknowledges it
and
the process variable
returns within the limits.
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