PLC-5/40L change to 5/80B

[mgeary 0]

I recently changed a PLC5-40/L to a 5/80B with a 1785-ENET sidecar.The problem was the scan time on the 5/40 was 30ms and the scan time of the 5/80B was cycling 60-120ms. The program is the same and the I/O configuration is the same, these are RIO on channel 1B. Chassis 1 16 slot 1/2 slot addressing Chassis 2 16 slot 1/2 slot addressing Chassis 3 16 slot 1/2 slot addressing Chassis 4 SLC 4 slot PanelView 550 on RIO. There are 2 MSG instructions with other PLC-5's via DH+. The only device using ethernet is a RSView station and with it connected or disconnected the scan did not change. According to the powers that be, the series and revisions are compatible.

[PLCMentor.com 60]

I would think the 5/80 would be faster also. With that said, have you tried removing the ethernet module to see if that is affecting your scan? I know you removed the cable, but I am talking the whole module. I have added those modules in the past and have not been aware of any big scan changes such as what you have observed, but that seems to be the only change other than the processor. You might want to let your post "marinate" for awhile and see what others have to say, but without any other solid reason, that would be my first troubleshooting step. Russell

[Ken Moore 23]

My guess would be the sidecar also. Since you have an 80B instead of an 80E. The main processor must read/write data through the backplane to the sidecar each scan.

[Ken Roach 194]

Were you not using the Local I/O port of the 5/40L controller previously ? My recollection is that in the heyday of the PLC-5, the 5/40 versions were the fastest and the "large-size" PLC-5 controllers had extra memory access and RIO capacity grafted on to their firmware and would solve logic more slowly in some applications. I'm surprised by a more-than-doubling of the scantime, though. What are the Series letters and firmware revisions of the two controllers ?

[Ken Moore 23]

Ken Roach made me curious. About five years ago, we expanded a process that was being run on a 5/40E, and had to upgrade to a 5/80E to handle the additional I/O and logic. The first step was to swap out the processors during an outage (no additional logic or I/O at that time.). I pulled up the archived programs, the scan time increased about 30-40 msec. So I guess Ken was correct, the 80's are a tad slower, but have much more capacity.

[mgeary 0]

There was not a local chassis used, there is an identical line that uses the local chassis. The new hardware versions are: 1785-PLC 5/80B series D f/w B 1785-ENET Rev B01 series B f/w A

[mgeary 0]

SOLUTION ! ? I swapped the PLC 5/80B series D with a PLC 5/80B series E using the same 1785-ENET and all is well. The scan time is right around 30ms. Still not sure if it was the processor or just the series of the processor. Thank you all for your input.

[Bill Wiewandt 0]

I swapped the PLC 5/80B series D with a PLC 5/80B series E using the same 1785-ENET and all is well. The scan time is right around 30ms. Still not sure if it was the processor or just the series of the processor. I'm not sure if I am remembering this correctly or not but it seems to me that a certain vintage of 5/80's were slower than previous versions. Later versions were then improved to be faster once again. Also, as Ken Roach stated, I believe the 5/40's were generally considered the fastest in the family.