Emerson Exchange 365

I would not expect to see a significant change in control CPU. (Control Expansion).

The Localbus (railbus) is polled on a fixed rate and the data is placed in the Controller's IO map and the modules read/write to this IO map. Slowing the scan speed of the Profibus Card will slow the bus down, which means the data will be updated in the Card at a lower frequency. However, if the Profibus scan is still completing faster than the LocalBus scan of the card, then the LocalBus will still see the same amount of data to be moved back to the controller.

For control expansion, you have three options:
- Slow Down faster modules,
- Modify Modules an use Block Scan Multiplier to reduce loading of certain modules,
- Off Load modules to another controller.

The EXEC_TIME parameter provides an approximation of CPU loading per module. It reflects the time the module Occupies the processor. Note that the value seen includes any interrupts that may happen while the module is executing so don't panic if you see some modules of the same class with a higher EXEC_TIME than an identical one. Use the more common value observed .

Slowing down the modules with the highest EXEC_TIME gives you the biggest bang for the buck, especially moving from 100ms to 200ms. A 100 ms module has 10 times the CPU loading as an identical module running at 1 sec.

Configurations that are heavy in Structured Text (CALC, ACT, CND, ACT, DCC) expressions will use more CPU versus using a built for purpose FB.

If your OnTime percentages are all 100%, and you are above 0 on the Control Expansion, you are good. It's not like a car that has a Red Line and if you stay there too long the engine will blow. But if you are at 0, then you don't know how "negative" you are. You should get Expansion value above 0.

An offline upgrade to a PK controller would also free up your CPU. The PK has nearly 8 times CPU expansion as the SX. But it needs more DIN rail space to install and requires an outage on the controller. You also have to make sure you have enough IO card power (Rail bus power), which may require keeping one of the Two wide carriers to house a pair of System power supplies. If that is an option, you don't have to modify any of the module scan times, Block scan multipliers or relocate modules.

Andre Dicaire