Connecting Lookout to AB Control Logix PLC through RSLinx

[DavidH]

I need to acquire a large number of digital values (~10000) from an AB Control Logix PLC via RSLinx. What is the best way to do this? Set up individual points in the PLC or pack the digital information into words? Which makes the most efficient use of the RSLinx to Lookout connection? I tried to use individual named boolean values but it seems to create a performance bottleneck. It isn't obvious (to me) if Lookout can internally pick bits from a word transferred in from RSLinx. This assumes that the performance problem is the RSLinx to Lookout connection. Is there a better way to approach this problem?

[John Dunlop]

Hi,

I would recommend collating the signals into words and passing them into Lookout and splitting them there. The comms overhead is much reduced this way (although you would need to do a bit of binary math in Lookout - see older tech notes).

One thing to be aware of - the control Logix PLC uses only 10% processor usage as default for servicing comms. We have found this to be too low. With this amount of transfer, you will need to increase this (in controller options).

You will find that the bottleneck is the PLC - PC not in OPC - Lookout. OPC is very quick (and exception based).

It may also be worth considering what signals you require fast and what is slow. You could set up multiple topics in RSLinx for different speeds.

Good luck.

John


PS: if you have problems with RSLinx it may be worth trying another OPC server e.g. InGear . I think Rockwell are taking lessons from Microsoft in "fatware".