Scan time trials
I just completed a project using a Unitronics Vision 280, the flagship of the line. I got the premium model with all the bells and whistles.
Now, one weakness of this product line is that it uses the same processor for scanning the HMI portion of the code as the PLC portion. This means scan times can get pretty hefty, averaging 60 milliseconds in my case.
I have over 80 subroutines in this program, covering 5 stations and the overhead system logic. Becuase I use integer state logic, only 20 of these are scanned at any given time. In the longest single routine, I used jumps to bypass the nets that aren't needed for that machine state.
My point is, I started out with an empty controller at 60-70 ms, and now with a completed program I'm at 60-70 ms, so most of that value is screen overhead.
Now, the bottom line - this was a retrofit job, replacing an obsolete Superior Electric motion controller. When finished, the machine is running at the same production output rate as it was when delivered, about 7 or 8 years ago.
I personally think scan time is important only in dedicated servo control applications, and certain very-high-speed situations. Ultimately, the machine is constrained by it's physical limits far more than the speed the controller is running at.
Incidentally, if I'd used the CANbus option and networked some M90s into my stations, using the V280 for system overhead, I'd have had a much faster average scan time, methinks
So there are always ways to improve it.
TM