PLC5 IO to Controllogix via ControlNet

RalphKitts

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Join Date
May 2006
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Alpharetta, GA
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A customer is wanting to use their 1771 IO and a Controllogix processor to take advantage of the newer features of the Controllogix platform. The plan is to use a small CLX rack with a processor with a ControlNet card, then add a 1771-ACN15 in place of the PLC5 processor.

I have run the conversion utility in RSLogix5000, and I have some questions: 1.) Can I add modules to the project offline? (I don't appear to be able to do this) If not, this will likely make my time at their site a little more stressful. 2.) What will the IO look like once I am onsite and connect, and am ready to alias the tags? 3.) What is the difference in the BTR/W instructions for the analog IO?

I am continuing to search and read what I can find, but any help from someone who has done this would be much appreciated.
 
On a different note... when you have old PLC5 or even PLC3, with lots of ASB remote I/O modules, why don't people typically replace them with this 1771-ACN15 or the redundant model so you can keep all your I/Os then control it by control logix 5000? Typically what I've seen is to recommend Control Logix rack with 1756-DHRIO module to control the Old PLC racks.
 
1.) Can I add modules to the project offline? (I don't appear to be able to do this)
Yes, you add 1771-ACN15 offline. No other I/O modules will be in I/O configuration. For all analog modules you will use Block transfers, like you did with Remote I/O

2.) What will the IO look like once I am onsite and connect, and am ready to alias the tags?

You will not see any I/O in RSlogix 5000. All descrete modules will be handled by rack optimized connection of ACN15
All Analogs will require Block transfer.

3.) What is the difference in the BTR/W instructions for the analog IO?

Controlnet PLC5 does not have Block Transfers, all done in RSnetworx. With Logix you will have to use BTR/W

I am continuing to search and read what I can find,

Appendix D of this manual has all info you need
http://literature.rockwellautomation.com/idc/groups/literature/documents/um/cnet-um001_-en-p.pdf
 
Last edited:
RalphKitts said:
A customer is wanting to use their 1771 IO and a Controllogix processor to take advantage of the newer features of the Controllogix platform. The plan is to use a small CLX rack with a processor with a ControlNet card, then add a 1771-ACN15 in place of the PLC5 processor.

If this is a single rack PLC5 system, this is the simplest way to do it. If it was a mulitple rack system using RIO, then I would probably use a 1756-DHRIO and replace the processor with a 1771-ASB. You do need to look at throughput if you have a lot of analog I/O and update it fast. However, many existing systems will operate just fine with this type upgrade.

I have run the conversion utility in RSLogix5000, and I have some questions: 1.) Can I add modules to the project offline? (I don't appear to be able to do this) If not, this will likely make my time at their site a little more stressful. 2.) What will the IO look like once I am onsite and connect, and am ready to alias the tags? 3.) What is the difference in the BTR/W instructions for the analog IO?

When you configure your I/O in RSLogix5000, all you will see is the 1771-ACN15 module under the 1756-CNB. You won't see any actual I/O cards like you would if you were using 1756 racks. You will get controller tags generated to represent the 1771 rack that you can alias or use as you like. The actual I/O will look like this...
ANC15name:I.Data[0].0 is the first bit of an input card in the first slot.

Once you add the 1771-ACN15 module to your offline program, you can see how it all works. No need to wait until you get to the plant.

I am continuing to search and read what I can find, but any help from someone who has done this would be much appreciated.

Good luck
 
Last edited:
georgeofthejungle02 said:
On a different note... when you have old PLC5 or even PLC3, with lots of ASB remote I/O modules, why don't people typically replace them with this 1771-ACN15 or the redundant model so you can keep all your I/Os then control it by control logix 5000? Typically what I've seen is to recommend Control Logix rack with 1756-DHRIO module to control the Old PLC racks.

The key bit of information there is "lots of ASB remote I/O modules". The cost of replacing them is not insignificant. For many systems, the 1756-DHRIO approach works very well. If you need the performance of ControlNet, then by all means go the 1771-ACN15 route. But I think you have to demonstrate a real need for it in most cases.

I know of one system that was upgraded from a PLC-3 that has 40 racks of 1771 I/O including 21 1771-IFE analog input cards. It uses 5 1771-DHRIO cards handling 8 separate chains of RIO. The analog I/O doesn't require fast updating, and it performs acceptably (pretty much the way it did before the conversion). Spending the money on 40 1771-ACN15 modules and installing new cable runs to the widely distributed racks would cost a lot and not provide much benefit. Not to mention the downtime required, which was a big factor. The conversion using DHRIO required very little downtime and very little risk. You could literally switch back in a few minutes if something didn't work out.

It all comes down to what makes sense for your situation.
 

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