PLC5 Maximum RIO Question

[Andrew Evenson]

Hi all,

Quick question about maximum RIO for a PLC5. I'm looking to add some a RIO drop that emulates 6 racks to my existing PLC5 system (It is being used as a RIO gateway). This is being done as an intermediate step towards a plc upgrade. In the PLC5 quick reference, it says that a PLC5/40E, which is what I am using can accomedate up to 60 Remote chassis or "15 I/O Racks" in brackets. So does this mean I can have 60 logical devices/racks on the network represented by a maximum of 15 physical devices?

Attached a snippit of the PLC5 qucik guide where I am referencing my info from...

Kind Regards,

Andrew Evenson

 

[joseph_e2]

There are some folks on here who are far more experienced with the PLC5 system, but Rockwell made the unfortunate decision at one point to use the word "rack" to mean 8 IO groups, each group consisting of a 16-bit word. So a rack would be 8 16-bit IO words, or 1920 IO points. So, a "rack" is a logical entity rather than strictly physical. Attached is the PLC-5 addressing manual (Pub 5000-6.4.4), which I can't find on RA's site any more.

 

[Andrew Evenson]

joseph_e2,

Thank you very much for your reply! So, if I understand you correctly, it's really the max logical I/O alowable represented in total bit, regardless of how may physical devices are on the network...

Thanks,

Andrew

 

[joseph_e2]

Weelllllll.....there's a physical limit too. A max number of modules per channel, as I recall. I could be off on that, though. You also get to have the joy of looking into 1/2-slot, 1-slot, and 2-slot addressing.

 

[Operaghost]

There is a physical limit to how many RIO adapter (chassis) you can have. That is the 60 you are seeing. But it would be very rare that anyone would reach that number. The maximum number of Racks is the more likely limit. Your PLC-5/40 allows Rack 00 - 17. That is sixteen total racks. Rack 00 is where your CPU is located, so that leaves up to 15 potential remote I/O racks.

As mentioned, racks and chassis are not the same thing. You can have up to 60 remote chassis, but only up to 15 remote racks. Understanding the difference is a whole other discussion that will take a substantial amount of time to cover. Let us know if we need to delve into that topic.

OG

 

[drbitboy]

17[/B]. That is sixteen total racks.

N.B. that is not a typo. Gonna rename OG as OctalGhost .

 

[Operaghost]

Just when you think you've escaped octal, it comes back and slaps you across the face to remind you it's never going away and you will never be free from it.

OG

 

[drbitboy]

I worked, briefly, in a nuclear plant on a 24-bit (24+parity) GEPAC 4020 with heated core memory. The experienced guys wrote a three-instruction program, using three fingers (one octal digit) on load-memory switches at a time that wrote a 0 at address 0, incremented the address counter, jumped back to the start fo the program, wrote another 0 at the next address, etc., to clear all of memory. It was actually pretty simple.

 

[ASF]

I was removing a PLC-5 recently and replacing it with a point I/O rack to an existing Control Logix. I had the site guys trying to ID all the sensors that we had to retain and migrate, and so they'd painstakingly gone through every j-box and recorded all the wire numbers, which referenced I/O, and then I was cross matching the ones to be retained in the program.

One sensor I just could not find. It was input I:09/11 but as hard as they looked, the site guys could not find a sensor with that wire number on it. In the end I got them to go there when the line was down so they could flash all the sensors on and off while I watched the input.

I found it. It was I:09/09.

The b***ards building the panel in the 80's put decimal wire numbers on octal inputs. So the first 8 inputs matched, and the second 8 did not.

 

[Ken Roach]

If you want real fun, use 1746 SLC-style I/O modules with a RIO adapter with a PLC-5; they're labeled in decimal on the indicator lights.

I think FLEX I/O came with both octal and decimal label cards.

 

[Phil Buchanan]

If you want real fun, use 1746 SLC-style I/O modules with a RIO adapter with a PLC-5; they're labeled in decimal on the indicator lights.

I think FLEX I/O came with both octal and decimal label cards.

That is loads of fun. We had these conversion kits for the SLC modules that changed the indicator labeling to Octal. Don't remember the kit # but it was OEM from AB.