PLC5 Rack As RIO For ControlLogix

tgoulding

Member
Join Date
Jan 2005
Posts
84
We intend to upgrade a PLC5 control system to ControlLogix. It is our intention to use the existing PLC5 I/O by removing the 5/25 processor and replacing with a 1771-ASB and connectiong via RIO to a 1756-DHRIO card in the new ControlLogix chassis.
Setting this up looks reasonably straight forward to talk to the Digital I/O, however we are a little unsure as to how to approach the Analogs. Has anybody done this before and if so your help would be appreciated.
 
tgoulding said:
We intend to upgrade a PLC5 control system to ControlLogix. It is our intention to use the existing PLC5 I/O by removing the 5/25 processor and replacing with a 1771-ASB and connectiong via RIO to a 1756-DHRIO card in the new ControlLogix chassis.
Setting this up looks reasonably straight forward to talk to the Digital I/O, however we are a little unsure as to how to approach the Analogs. Has anybody done this before and if so your help would be appreciated.

I have done a few PLC5 , PLC5/250, and PLC 3 conversions to Contrologix. The 1771 analogs are treated the same with BTR and BTW instructions except using the MSG instruction, which has the Block Transfer Reads and Writes as a message type.

Another option would be to go Controlnet, but I realize the RIO 'blue hose' is already in place.

Ian
 
Thanks for that. Found a Tech Note on Rockwell website with respect the SLC RIO and ControLogix using MSG blocks, I guess it's along similar lines
 
tgoulding said:
Thanks for that. Found a Tech Note on Rockwell website with respect the SLC RIO and ControLogix using MSG blocks, I guess it's along similar lines

Make sure you have V15 of Contrologix and the CPU has V15.05 firmware (V15.03 & V15.04 have an issue). There were issues with the number of MSGs that could be active at one time with previous versions of Contrologix.

Ian
 
The number of cached Block Transfer type MSG instructions was changed way back in v10, so you can have 32 BT type or MSG type in any mix, per CPU (not per DHRIO).

That is an important limit to consider in design of large legacy migration systems like PLC-3. But for your one-rack replacement of a PLC-5/25, it's not a problem.

Carefully examine and capture the data in the configuration and data BT's for your analog cards; you'll have to manually re-create that in INT arrays in ControlLogix.

There are a few technotes and a User Manual for the conversion utility. Plenty of stuff to chew on, but you've already pointed out the most significant consideration for I/O addressing.
 
Also see technote G19357: Using User Defined Structures for Block-Transfer Modules with ControlLogix. Using UDT's makes the configuration and data retrieval MUCH easier than using an INT array.
 
and something else ...

you might want to consider speed/throughput issues too - since your analog modules USED TO BE "local I/O" and now they're GOING TO BE "remote I/O" ... in some (most?) systems this isn't an issue ... in other systems it's critical ... just be aware that the signals won't go through as fast as they used to ...
 
tgoulding said:
We intend to upgrade a PLC5 control system to ControlLogix. It is our intention to use the existing PLC5 I/O by removing the 5/25 processor and replacing with a 1771-ASB and connectiong via RIO to a 1756-DHRIO card in the new ControlLogix chassis.
Setting this up looks reasonably straight forward to talk to the Digital I/O, however we are a little unsure as to how to approach the Analogs. Has anybody done this before and if so your help would be appreciated.

Smart move if you ask me. Nothing is more rugged than 1771 I/O. Like Ron said, make sure the new system meets your scan requirements. We converted a system from PLC5 to CLogix many years ago and found that speed was not an issue. The PLC program was 4 times faster even though it was 5 times larger. C-Logix gives you the flexibility to specify scan rates of all I/O on C-Net and local connections. Some of out remote I/O was much faster than our original PLC5 local I/O because of the choices we made...
 
Also, on the digital side--don't forget the 1771 i/o is addressed octal, logix is decimal. maybe you could create Octal based alias tags to ease the transition for the maintenance guys when they look at hard addresses as opposed to internal bits.
 
C-Logix gives you the flexibility to specify scan rates of all I/O on C-Net and local connections.
I just want to make sure that people understand that this avaialble over CONTROLNET only.
Converting RIO cabling and adapters to ControlNet may be costly project.
Leaving RIO in place may not give you required perfomance with large system.

Also before making decision to keep 1771 I/O ask your self few questions:
- how many 1771 module I replaced within last couple years?
- how old majority of these 1771 I/O modules, adapters PS and racks.
- do you have a bad I/O points that you alredy bypassed?
- for how long this system will be in production?

1771 I/O is very solid platfom, but electronic devices are known to degrade with age:
corrosion,
capacitors going bad,
spring loaded contacts are getting weak etc.
and this is a natural non-reversable process.

1771-I/O modules are very expensive and replacing failed modules only may be costly idea.

If your system already over 10 years old and you need another 15+ years from this I/O you may be better to replace it with Logix I/O as well right now.
 
I am also trying to convert a PLC2 to a Remote i/o chassis to Controllogix. I purchased a 1771-ASB module and a new chassis (1771-a3b) to install the i/o. Programming and I/o seemed straightforward, but when trying to get the remote i/o card to speak with the asb module, I ran into problems. I could never get the link light to work on the ASB.

At first there were no lights whatsoever, then I began "playing" with the switches. I got the light to go green when setting the switches for 2 slot addressing. This however is wrong as I have all the input cards first then the output cards, then the analog input module.

12 slot chassis is...6 16pt input cards (ac), 2 16pt output cards (ac) 1 32pt output card (ac) 1 analog input card, and a power module in the last slot.

I started this project as I heard this is a common upgrade and is not problematic. After my problems, I read a post somewhere that said the 2 slot addressing is the only way this will work. I have also read that this is not true, and 1/2 slot, 1 slot and 2 slot are all viable.

Anyhow, I believe that my problems are just in the switch settings, but I spent an hour "playing" with the system down and did not get it to work. I put the original PLC back into the chassis to keep running until I figure out what was wrong.

Thanks in advance for any help you can provide.

Best Regards,
Michael
 
palmer_md said:
I am also trying to convert a PLC2 to a Remote i/o chassis to Controllogix. I purchased a 1771-ASB module and a new chassis (1771-a3b) to install the i/o. Programming and I/o seemed straightforward, but when trying to get the remote i/o card to speak with the asb module, I ran into problems. I could never get the link light to work on the ASB.

At first there were no lights whatsoever, then I began "playing" with the switches. I got the light to go green when setting the switches for 2 slot addressing. This however is wrong as I have all the input cards first then the output cards, then the analog input module.

12 slot chassis is...6 16pt input cards (ac), 2 16pt output cards (ac) 1 32pt output card (ac) 1 analog input card, and a power module in the last slot.

I started this project as I heard this is a common upgrade and is not problematic. After my problems, I read a post somewhere that said the 2 slot addressing is the only way this will work. I have also read that this is not true, and 1/2 slot, 1 slot and 2 slot are all viable.

Anyhow, I believe that my problems are just in the switch settings, but I spent an hour "playing" with the system down and did not get it to work. I put the original PLC back into the chassis to keep running until I figure out what was wrong.

Thanks in advance for any help you can provide.

Best Regards,
Michael

First place to start is to figure out what baud rate the existing RIO is operating at. The 1756-DHRIO baud rate is set via rotary switch on the card.

Also, The 1756-DHRIO is not capable to autoscan the RIO, therefore , you must manually configure the racks in the DHRIO 's configuration tree.

rio_jpeg.JPG




Start off by having the 1756-DHRIO and the 1771-ASB set at the same baud rate. Then make sure the rack addressing and size match the size of the rack you wish to scan.

Also pay attention to the pins the Blue and Clear wires of the blue hose are connected to and if need be, flip them at the Clgx end.

Once you download the programming and configuration the the Clgx CPU, place the Clgs PLC in RUN, then examine the RIO status.

Its a start
 
Last edited:
This is pretty common, and fairly straightforward. Having the I/O configuration is a crucial first step.

Type "1771-ASB DHRIO" into the Knowledgebase search engine and up comes Answer ID # 17625, "How to configure communications from a 1756-DHRIO to a 1771-ASB". This will show you the basic configuration in RSLogix 5000.

You can't use 32-point cards with 2-slot addressing, so that's out. Is there a gap somewhere in your slot assignment description ? I'd expect the 32-bit Output card to be adjacent to a 32-bit Input or an empty slot if you are using 1-slot addressing.

Do you know how the current chassis is configured ?
 
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Ken Roach said:
This is pretty common, and fairly straightforward. Having the I/O configuration is a crucial first step.

You can't use 32-point cards with 2-slot addressing, so that's out. Is there a gap somewhere in your slot assignment description ? I'd expect the 32-bit Output card to be adjacent to a 32-bit Input or an empty slot if you are using 1-slot addressing.

Do you know how the current chassis is configured ?

I am very familiar with both the PLC5 and ControLogix platform, so I thought this was going to be an easy conversion.

I set the switches on the adapter/chassis for 1/2 slot addressing, and set the PLC to scan for 3 Racks of i/o. All the settings are for 57.6kbaud. Wiring between the RIODH+ card and the adapter is correct, with termination resistors at each end.

The interesing thing was that when the original settings did not show a link light, I began to "play" with the switches and when setting for 2 slot addressing, I was able to get a link light. the PLC noted that there was an error due to a card not in the correct location (which was true 2 slot addressing).

I also tried setting the adapter/chassis for Rack 0 and then for Rack 1. I tried scanning for Rack 0-2 and for 1-3 in both cases without success.

Without the autoconfigure feature like the plc5 has its difficult to determine what the scanner is "seeing" at any given time.

Michael
 

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