SLC to CLX, and other questions

the_msp

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May 2008
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Northern Ireland
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In 2009 I successfully completed 2 projects. The 1st, was to replace two machines controls that were using SLC 150's (with expansion units) and 1745-TCAT's as the HMI. The TCAT's were the driving reason, we couldn't get spares and it was costly to have them repaired. The second was on a third machine, same function just a newer version, that had a SLC 5/02 and a DTAM as the HMI. Again, the HMI was the driving reason. I upgraded to a 5/03 and installed a Panelview 300 (2711-K3A2L1).

Now I am potentially looking at a similar project again, only this time with 15 machines not 3.

The PLCs are 5/02's with DTAMs. The client wants 15 new panels, and new field hardware (pneumatics located in the base of each machine). This is within a food plant, so wash down environment with caustic a plenty.

My first question, would anyone consider in this situation replacing the 15 currently stand alone PLCs with a single (or redundant pair) CLX? On one hand, if the PLC (if not redundant) went down, you lose 15 machines, not one. But on the other, the PLC is the most reliable part of the puzzle, right? If there were 15 programs in the CLX, one for each machine - would it be >= 15x processing power of a 5/02? The SLC program used 1717 Instructions (2902 data table) leaving 2919 Instruction words left in a 4K memory. 32 Digital In and 32 Out, no analogs.

Secondly, I see the PV micro 300 (and it's brothers) are now obsolete. What would you recommend as a current day replacement?

Thirdly, the machines were designed with hard wired (relay) interlocks. Not so much for operator safety reasons, but because if two cylinders extended at the same time, they would bend each other. If I were to go hi-tech and put in an E/IP headed pneumatic manifold bank - would you consider software interlocks sufficient?

I will of course be contacting my local AB rep with the above questions, but it's good to get some unbiased and experienced opinions.
 
My first question, would anyone consider in this situation replacing the 15 currently stand alone PLCs with a single (or redundant pair) CLX?
To answer your question with another question: what, if any, interaction is there between the machines? If they are truly stand-alone, I would consider going with 15 CompactLogix processors rather than larger 1756 ControlLogix units. Not sure you'd be money ahead, but it would be nice to have everything in one washdown box. I've worked in plenty of food plants over the years and water/chemical ingress avoidance is a very good thing.

Secondly, I see the PV micro 300 (and it's brothers) are now obsolete. What would you recommend as a current day replacement?
Check out Red Lion HMI for this type of application. Much less expensive than the Rockwell solution, especially if you're looking at one HMI/unit.

Thirdly, the machines were designed with hard wired (relay) interlocks. Not so much for operator safety reasons, but because if two cylinders extended at the same time, they would bend each other. If I were to go hi-tech and put in an E/IP headed pneumatic manifold bank - would you consider software interlocks sufficient?
Just to make sure I understand, it sounds like you're talking interlocks from output coils, not prox switches or other PLC input devices. My theory is to consider replacement cost of the cylinder vs. hardware/space cost of the interlocks. What's the likelihood that one of these outputs gets forced on? That's the type of situation where bad things tend to happen with software interlocks alone.
 
To answer your question with another question: what, if any, interaction is there between the machines? If they are truly stand-alone, I would consider going with 15 CompactLogix processors rather than larger 1756 ControlLogix units. Not sure you'd be money ahead, but it would be nice to have everything in one washdown box. I've worked in plenty of food plants over the years and water/chemical ingress avoidance is a very good thing.

They are truly stand alone. My reason for going CLX would be I could locate it within a dry control room, away from any wash down. And thus have a smaller panel in the field. I was on another site 5 years ago that had 3 of these, a later model than the first two models I had worked on. They had 1 larger panel for control, which I didn't get to see inside, but it only had one HMI (PV 600) so I assume only 1 PLC. The 3 local machine panels were very small, only had a couple of PB's and an E-stop.


Check out Red Lion HMI for this type of application. Much less expensive than the Rockwell solution, especially if you're looking at one HMI/unit.

Yes would be one per/machine.


Just to make sure I understand, it sounds like you're talking interlocks from output coils, not prox switches or other PLC input devices. My theory is to consider replacement cost of the cylinder vs. hardware/space cost of the interlocks. What's the likelihood that one of these outputs gets forced on? That's the type of situation where bad things tend to happen with software interlocks alone.

Now your testing my memory... haven't been inside one of these panels for around 5 years. The (current) panels have manual H-O-A toggle switches, which do not go to the PLCs at all. They are hardwired to relays which, through hard wired interlocking, make sure you can't extend two opposing cylinders.
 

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