STI Equivalent in GE 90/30

Does anybody know if the GE 90/30 have an equivalent (AB) STI feature? If not, are scantime and timer accurate enough for PID instructions?


Thanks in advance for any advice.
sang

The 90-30 has a timed subroutine feature.

One of the setup parameters for the PID instruction is the recalculation time. The function will be recalculated and the PV updated in the scan in which the recalculation time has passed.

I do not know of an STI PID interface for the 90-30, there is for 90-70 and RX7i and maybe the RX3i.
How fast do you need to process the PID? If my memory is intact I think the 90-30 will attempt to process every scan but that is not guaranteed.
A fast CPU like the IC693CPU374 may have a scan of 3-5 mSec. or as much as 10-15 mSec. with a lot of process logic in place. But then you also need to take into account the Analog I/Q update times.
Then again you can play games with the "DO I/O" and Interrupts etc.
Not an easy question to answer.

The PID function in a 90-30 will not execute faster than every 10 milliseconds. If you set the "Sample Period" parameter to zero it will execute as often as possible which will be every scan or every 10 milliseconds, whichever is slower.

If you set it to execute every 10 milliseconds and the PLC scan time is 8 milliseconds, it will execute every other scan.

If speed is an issue, you may be able to find a PID function block written in C that you can run in the 90-30 and execute faster than once every 10 milliseconds. I remember a GE Fanuc AE telling me about it several years ago when I was converting a Series Six application to 90-30. The original application had a stand-alone loop controller and I was bringing that function into the PLC in the new system.