C300 Controller Overload Conditions - Honeywell Experion C300 User Manual

C300 Controller overload conditions

The C300 Controller is able to handle overload conditions when the controller is required
to perform more work than it has time for. The execution of control strategies or control
processing usually demands the most resources, in terms of processor time, and is the
most likely cause of an overload condition in a controller, (other non-control processing
causes can produce controller overloads). When the C300 controller detects an overload,
it will 'borrow' time from control execution by suspending control processing in a
defined and predictable manner. This allows the controller to continue operation, to
provide control and maintain communication under these conditions.
The result in the controller is that control degrades gracefully, in the sense that latency in
control loops increases. Also, a significant amount of processing time is made available
to the controller so that it can handle the backlog of tasks that result from an overload.
Alarms and event are generated to alert operators of the controller overload cause so that
actions can be taken to alleviate the overload.
How to avoid controller overloading
Planning your control strategies will help to avoid overloading a C300 Controller.
Develop a performance model to determine whether or not a C300 Controller has the
resources to execute the planned strategy. Test the strategy before loading it to the
controller.
During operation pay attention to warning alarms associated with low values of 'CPU
Free' and overloads when control strategies are loaded incrementally to the controller.
Overloads also may occur when a large control strategy is loaded at once, such as a
Checkpoint restore or a bulk load, rather than incrementally.
Alarms and parameters are associated with processor use in the C300 Controller are
•
CPUFREEAVG, CPULMLO and CPULMLOLO. These and other related
parameters are found on the Main tab and the Statistics tab of the C300 block
configuration form.
Parameters that measure the ability of the controller to execute loaded control
•
strategies are CPUCYCLEAVG and CRCYCLEOVRN. These and other related
parameters are found on the CPU Loading tab and the CPU Overruns tab of the
CEEC300 block configuration form.
Using the following guidelines will help to avoid overloading the controller:
The controller should operate in the steady state without persistent overload alarms
•
of any type.
The controller should operate in the steady state without CPULMLOLO alarms
•
The controller should operate in the steady state with an average CPUFREE of at
•
least 20%
R301.1
11/06
Experion C300 Controller User's Guide
Honeywell
C300 operating behaviors
C300 Controller overload conditions
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