Total System Load and Cyclic Load of AC800M controllers
What are the optimum and maximum values for PM864 and PM866 AC800M controllers for the following parameters:
Total System Load
I am asking this question as one of our customers have a controller with total sysem load at between 90% to 93% and cyclic load at 49%.
At what point does the controller become unreliable in terms of MMS communication signals dropping, scans missing etc.
Voted best answer
the total system load and cyclic load can be "110 %" as long as it executes what is it told to execute.
Normally you can start to get problems at 70% cyclic load, but the easiest way to figure out if the controller is overloaded or not is to right click twice on the RNRP "R" shortcut which is located in the lower right corner of your screen, on Connectivity server.
Menu item 5 "Response time", enter the ip address of the controller. If the response time is longer than 100 ms, then you should verify the task offsets, and if it is OK and still > 100 ms, then your controller has too much to do...
Irrespective of the type of controller like PM864A or PM866 here the only diffrence is speed & Memory i.e PM866(64MB RAM)=1.4xPm864(32MB).
Cyclic load =Execution of IEC61131-3 code which include Application size,Task time,Copy in/out Communication variables the load shouldnot go not more than70% if the load crosses the limit then load balancing parameter in the controller task wil automatically increases the task interval time to re-establish the 70% load.
Note:we can disable this loadbalancing only AC800M HI controller by Overrun & latency supervision.
Systemload=Cyclic Load+Communication handling like ethernet,CEX bus,Serial Channels
Communication handling has the lowest priority in a controller. It is therefore
important to consider controller CPU load if the communication handling is vital to
the application. Running close to 100% total load will result in poor capacity and
response times for peer-to-peer and (OPC Server for AC 800M) communication. It
is recommended that peak total load will be kept below 100%.
Among the communication protocols, the IAC MMS protocol will be the last to be
affected if there is a communication data starvation.
Please refer the manual for more info. from page no 109 onwards
Note: For AC800M HI Controller
Recommended Parameters are