The I/O scan time of a PLC5/25 is to long

[mulderm 3]

Hello, I have a DH+ network with the old classic PLC5/25 processor. Now I think the scan time is to long so that scanning an input is always have a different moment. How can I measure the I/O scan of the processor? What is the I/O scan of a PLC5/25 processor and what of the new type are available to replace this PLC5/25 with a faster I/O scan? Who knows? Greetings, mulderm

[TimWilborne 108]

Rockwell just released a technote with some info on the differences between the Classic and Enhanced processor. You can view it HERE

[Gerry 13]

The 'new platform' PLC5's will give you a much faster program scan, but I doubt you'll gain much if anything on the I/O scan. One thing that will impact heavily on program scan is allowing the block transfer queue to fill up (by triggering them faster than they can be serviced).

[Ken Moore 23]

I use the 5's in process control, so analog update time isn't usually a factor. I always use a "cascade" scheme for my block transfers. BT1 is started by a fist scan or if the last BT is done or in error, then BT2 is started when BT1 is done or in error, BT3 is started when 2 is done or in error, right on down the line. Never had an issue with queue filling up.

[JesperMP 2]

I guess that mulderm is referring to the "i/o scan" as time between updates of the i/o. I dont think he is referring to the fraction of the total scan time that is used to update the i/o image tables. The latter would to my opinion be interesting but useless information. System status word S:8 contains the last scantime in milliseconds. Enhanced PLC5 CPUs execute code approximately 4-5 times faster than classic PLC5 CPUs.

[mulderm 3]

Thank you for the information guys. mulderm