ControlLogix and 1771 I/O

Anyone out there doing this?

I have a PLC5 system in place that uses 1771 I/O. I'd like to replace the PLC5 with a C/L processor and set up the 1771 I/O as remote I/O using a 1756-DHRIO and a 1771-ASB.

Right now, I have the C/L and 1771 rack set up at my desk. The ASB module I have is old (series B) and it won't talk to the DHRIO, so I'm wondering if there is an issue between the DHRIO and a series B ASB. I hope not, as the system I want to convert has about 8 remote racks and all of them have series B ASB modules in them.

I'd appreciate any shared experience with a project like this.

Jeff

Check your DHRIO configuration and try the wiring with opposite polarity. The 1771-ASB Series B module should have no problem communicating with a 1756-DHRIO scanner.

There are some RA Knowledgebase documents about PLC-2 to PLC-5 conversion that are applicable to 1771 module compatibility, if you have extremely old gear like 1771-AS or PLC-2 scanner modules.

Search the Knowledgebase with the keywords "DHRIO" and "1771" and you'll come up with some useful information.

The usual limiting factor is the number of simultaneous MSG instructions the Logix is capable of. You need to use up some of these MSG connections to perform Block Transfers to 1771 Analog modules. If you have a large or analog-intensive system, you might run out of Logix MSG buffers.

Don't expect the same performance from a single DHRIO scanner port as you got from a PLC-5 RIO scanner port. Logix was built around CIP networking, and the interface to legacy networks is for migration purposes and interconnection purposes. Logix isn't meant to outperform PLC-5 on these older networks.

Thousands and thousands are doing it.

How do you know your network is working? Can you see the ASB modules in RSLinx? If you are connecting to your control logix through ethernet with an ENBT module then you should be able to bridge directly through to the DHRIO module to the ASB even with the processor module removed from the rack. If you are using a serial connection you should still be able to browse through the module and see the DHRIO network in RSLinx.

usmcgrover said:

Anyone out there doing this?

I have a PLC5 system in place that uses 1771 I/O. I'd like to replace the PLC5 with a C/L processor and set up the 1771 I/O as remote I/O using a 1756-DHRIO and a 1771-ASB.

Right now, I have the C/L and 1771 rack set up at my desk. The ASB module I have is old (series B) and it won't talk to the DHRIO, so I'm wondering if there is an issue between the DHRIO and a series B ASB. I hope not, as the system I want to convert has about 8 remote racks and all of them have series B ASB modules in them.

I'd appreciate any shared experience with a project like this.

Jeff

Click to expand...

I've done this many a time. Should work.
You may have a cabling, RIO baud rate, or configuration problem.

Unfortunately , Clgx does not have a RIO scan utility to 'sniff' who is on the RIO network.

I have a system with 14 racks - they are split into two networks of 8 (4 16-slot chassis and 6 racks (3 16-slot chassis) each.

Be careful - the analog modules still require MSG (acting as BTW and BTR's). The ASB modules coupled with ControlLogix only allow a single message at a time. In my case I have 16 analog cards in each of 4 chassis. I had to utilize a "message manager" to logically control the MSGs to allow for only one per chassis at a time. Just a note here: I am using L55 processor and the IO update rate for 16 cards is about 5 seconds.

Another system we have, I upgraded to using ControlNet. This is definitely the way I would approach using 1771 IO. Better yet would be to upgrade the IO.

It works...

Thanks for the replies. The KB article was a big help. Sometimes it helps to read the instructions, even though most of us would rather not.

I'm just playing around with this in my spare time (not much these days) in anticipation of an upcoming project.

Most of my I/O is discrete. There are a few analog modules in the system used to read temperatures from PID controllers, but the data is not used to control anything so I don't believe a slight delay will be a problem.

Thanks for all you suggestions and insight. I'll be back if I have more questions.