A2SH(S1) "B" Link Relays

[Guest]

Mitsubishi A2SH(1) One frame, no expansion. Besides P/S and CPU it is populated with two X42 and two Y42 I/O cards and one blank left over.

Network type set as "None" in parmeters. All other parameters are at factory default. Using GX Developer V7.11M

Application: This PLC used to control product conveyance and automatic handling through machine by means of cylinders, actuators, position sensors, etc. Nothing unusual.

Problem: I have been assigned to modify one part of the product handling motion. I am not the original author of this code. In the rungs I need to modify there are "B" network link contacts controlling the action. Since there is no corresponding local "coil" in this program that usually means these contacts are controlled elsewhere on the network. Since there is no network, I am perplexed as I monitor and watch these B network link contacts go on and off as the program runs.

Question: How (or where) else might these B network be controlled? Obviously I need to fill a gap in my knowledge of how this works. I have been scratching my head alot on this one.

Thanks for the help.

 

[panic mode]

Can you post program here (or anywhere else) so we can
take a look at it?

 

[Tim]

Hmmm,
Sounds odd! Remember that the link relays can be used just like the M relays when your not using them in the link data network. If there is no buffer memory or something else thats not being accessed then I'm not sure. Is there any data being moved to those "B" relays in the main program? Maybe a command you've not come across yet. Is there a HMI hooked up to the plc? I guess you would have said if there was, just trying to trigger something. Do you see any TO or FROM or MOV cammands with "B" as being one of the destinations in the program?
Keep in touch
Tim

 

[Marty]

The answer:

Called Mitsubishi tech support and learned about a litle known (at least by me anyway) second processor in the A series PLC. Seems that one can run a process using this controller in a real multitasking situation along with the main CPU running the ladder code. This processor can read and write to the same memory as the main program.

Wala! Thats whats going on here. I could think of some situations where this would be nice to have, but why the original programmer used it for this I'll never know. Anyway, I haven't figured out yet what I'm going to do about it (The Mitsu guy told me this was never supported in the USA and the Japaneese interface is all but obsolete) as GX developer has no access to it.

Guess I'll just write some new rungs for what I need and put an always off relay in the old rungs and retreat!

Thanks for the replies

Marty Young, process engineer Keihin Corp
(have an account here at PLC.net, but forgot what it was)