Compact Logix upgrade

We are doing a upgrade on some of our equipment from a SLC500 to a Compact Logix. We used the conversion software that Allen Bradley suggested to use, but now with the new PLC installed, we are noticing some differences on how the machines run. We believe it is some kind of timing issue. The program has several one shots and timers in the program. What we are wondering is, does Compact Logix run faster than the old SLC500 as far as the scan time? If it does what do we have to do to get it to run the same as the old one?

Based on your description, I would compare like timers in the old and new programs to be sure the length of time specified for the CompacLogix (milliseconds) matches the unit count and time base used by the SLC.

The CompactLogix CPU performance, given 'identical' programming, is many times greater than SLC. I/O updates are also asynchronous to program scans, unlike SLC.

While the conversion software will get you close, you've got to do some manual inspection. Right off the bat check all timers, as the time units are specified in the SLC and are all ms in CLogix.

To give an example

In the SLC 500 the preset of 100 could either be 1.00 seconds or 100 seconds. In the MicroLogix it could even be 0.10 seconds. The SLC uses a selectable timebase.

In the CompactLogix the timebase is always milliseconds. So 100 would always be 100 milliseconds.

This is most likely where your issues are coming from. Not the faster scan or asynchronous I/O updates (which are true, but probably not the issue).

OG

The conversion software should put comments on rungs that need review, such as with the timers that have been suggested.

The other aspect could be the asynchronous IO update rate. You may need to buffer your IO to ensure the logic scans in the same manner as the SLC