what should be the minimum total system load and cyclic load of PM 865
We have ESD system in which we have used two PM865 for different plants. ONE PM865 controllers2(redundant) for our unit-1&19 and other PM865 controller1(redundant) for unit-6,8 and 16 , we noted our controller2 total system load 46%, cyclic load 8% and controller1 total system load 54%, cyclic load 13%. Toal tags alreday used are 426.
In future we need to add almost 200 tags for our new "unit 7 " to our ESD system. Please help me to select in which controller(controller 1 or controller) i should add these 200tags.
Can i go for new PM865 controller?
Details are below and system architecture attached.
ESD SYSTEM: ABB 800xA
LOGIC SOLVER: AC 800M HIGH INTEGRITY (HI)
· CONTROLLER:PM865 + SM810 REDUNDANT (1002) SIL 2
· DIGITAL INPUT MODULE: DI880, SIL3 digital inputs with SOE. 16 ch., 1 group of 16 ch., 24 V d.c., current sink, extended diagnostics , SIL3.
· DIGITAL OUTPUT MODULE: DO880 SIL3 digital outputs with wire-fault detection. 16 ch., 1 group of 16 ch., 24 V d.c., max. 0.5 A, current source, short-circuit-proof, extended diagnostics , SIL3.
· ANALOG INPUT MODULE: AI880A SIL3 analog inputs with HART interface. 8 ch., 1 group of 8 ch., single ended with common return, 0(4)-20 mA, 12 bit, extended diagnostics, HART interface, transmitter power supply, SIL3.
As advise only - hope this could give you some ideas:
- controller 2 seems to be less loaded
- both controllers are under the limit, cyclic load less than the limit.
From help file:
Cyclic load displays the percentage of the controller CPU power used for application execution of all tasks. If the cyclic load exceeds 70% in the controller a so-called load balancing is initiated automatically. The intervals for all tasks, except the time-critical task, are then generally increased to limit the cyclic load to 70%
- it is difficult to judge which load is created by tags. It depends on the application in the controller, also communication creates load (total load), functions, cycle time etc
- the best would be new controller, of course - in case the budget allows that. But first you could try with extentions of the existing controllers. CPU could be easy added, if the new code is in separate application
- how many I/O's you have to each controller?
- System load could be estimated in case you provide the existing and the final configuration.
For example redundant PM865HI with 400 DI880, 200 DO880 and 300 AI880 (7 IO clusters. almost full) and SIL3 reports 560 tags and estimated load is (only estimation !):
Cyclic load: 44.4%
Total load: 61.7
That should be OK