Control Loop Utilization Advisory (RMC200)

As described in the Loop Time topic, it is important that the actual loop processing time does not frequently or excessively exceed the selected loop time. For each selected loop time, there are a maximum number of axes for which the actual loop processing time is never expected to exceed the selected loop time, given a full load of motion commands, plots, user programs, and communications.

The Control Loop Utilization Advisory in the Axis Definitions dialog provides a graphical indication of how much of the RMC200's loop time is likely to be used given the current number of axes.

Axis Indicator

The Axis Indicator reflects the expected loop time utilization for all the currently defined axes, relative to the likelihood that the loop time will be exceeded.

If the axis indicator is in the:

Green: It is very unlikely that the loop time will be exceeded.
Yellow: There is a small chance that the loop time will be exceeded.
In order to use this number of axes for the selected loop time, the user must check the High Control Loop Utilization box in the Control Loop Page of the CPU Properties and verify that the application does not exceed the loop time excessively, as described in the Loop Time topic.
Red: There is a significant chance that the loop time will be exceeded.
In order to use this number of axes for the selected loop time, the user must check the High Control Loop Utilization box in the Control Loop Page of the CPU Properties and verify that the application does not exceed the loop time excessively, as described in the Loop Time topic.

It is rare for any application to have a full load of motion commands, plots, user programs, and communications. Therefore, in many cases, it is acceptable to choose a loop time that, given the number of axes, may be exceeded by a full load, because the full load will likely not occur. In these cases, selecting that loop time requires setting the High Control Loop Utilization check box and verifying that the application does not exceed the loop time excessively, as described in the Loop Time topic.

When is High Control Loop Utilization Required?

For the RMC200 controller, High Control Loop Utilization is required if the estimated axis processing time exceeds the processing time allowed for the selected loop time. The following tables are used to determine whether or not High Control Loop Utilization is required:

Maximum Total Axis Processing Time Allowed at Full Load

Loop Time	CPU20L	CPU40
125 µs	0 µs*	52 µs
250 µs	0 µs*	100 µs
500 µs	152 µs	302 µs
1000 µs	302 µs	not limited
2000 µs	not limited	not limited
4000 µs	not limited	not limited

*This means High Control Loop Utilization is always required.

Estimated Processing Time per Axis

Axis Type	CPU20L	CPU40
Single-loop Control Axis	11.9 µs	10.2 µs
Dual-loop Control Axis	16.0 µs	14.0 µs
Virtual Axis	7.9 µs	6.3 µs
Reference Axis	3.2 µs	2.5 µs
Output Only Axis	1.5 µs	1.2 µs

Notice that the estimated per-axis processing times shown above are conservative estimates assuming maximum processing, for purposes of determining whether High Control Loop Utilization is required. Actual processing time for axes will often be significantly less than these times indicate. However, the user should always verify that the application does not exceed the loop time excessively, as described in the Loop Time topic.