PLC 5 Remote I/O Adapter

I had a call from a pretty irate customer last night and just want to get your opinion on a few things.

We have just won quite a large contract with a company to install some new equipment. There is already a software company who have done a lot on site who submitted a tender at the same time as us, but lost.

This other software company are constantly making changes to PLC code on a daily basis.

As part of the contract we had to move some electrical panels. One of these panels has a PLC 5 remote I/O adapter connected with DH+. There are maybe 10 of these remote I/O panels but we only moved one.

To move the panel we obviously had to disconnect all power to the panel. When the panel was powered back up the PLC saw the remote I/O rack and valves etc were forced from the PLC and inputs were seen back at the rack and back at the PLC.

This was done on Tuesday night. I got a call last night saying that none of the valves on the remote I/O panel were operating.

After arriving on site and doing a few checks it became apparent that the remote I/O rack wasn't communicating, I would force a valve and the output wouldnt come on the rack, and if I put 24v across an input I didn't see the input back at the PLC. The remote I/O adapter light was telling me that it was active and there was no fault with the PLC. If I disconnected the DH+ The active light went off and the remote I/O adapter went into fault, reconnect and everything looked good on the surface, but still couldnt get any I/O working.

I then found out the other software company had added some remote I/O of there own and broke into the DH+ further down the line (my I/O rack being the last in the chain).

After talking with there rather obnoxious programmer who told me in no uncertain terms was he going to help us out because we were the enemy, I decided to do an auto configure of the adapter, and hey presto up she fired.

Why would turning the power off to the panel mean that an auto configure had to be done, surely the PLC holds all the address information, and the remote I/O adapter is basically a dummy back plane and as no dip switches had changed what went wrong. Could it be that someone that added another remote I/O adapter set a dip switch wrong and then realising what they had done quickly changed it so after doing an auto config it picked up my I/O adapter as it was before the changes were made.

Now I know what you all are thinking that I want to push the blame somewhere else but to be honest I just dont want another call at midnight and if it is going to happen everytime a panel is powered down I need to be aware of this for future work. If an auto config has to be done when a panel is powered down is there a way or a setting maybe where the remote adapter will auto config when powered back up.

I know this is a bit of a long thread but I could really do with trying to get to the bottom of what happened and why so i can stop it from happening again.

Any questions feel free to ask.

Thanks for your time

Mark

I'm not sure what caused your problem, but I might have a couple of pointers to help you describe it. You never connect a RIO adapter with DH+. They both use the same "Blue Hose" cable, but they are very different network protocols. It would be a Remote I/O network.

You also said that your rack was the last one in the chain, but the other company broke into the network further down the line. That doesn't make sense to me.

Have you checked the terminating resistors at both ends of the network? I have seen those cause problems, particularly when extending an RIO network. Those resistors should both be the same, and should be either 82 or 150 Ohm, depending on the network configuration. The rules for selecting which resistor value are kind of complex, so you should look them up in the manual and verify that you are using the correct ones.

Jimbo,

Sorry my mistake, yes it is still a remote I/O network using the same 'blue hose'.

The remote I/O is daisy chained with my panel being the last on the chain, all the terminating resistors are installed. From what I can gather from what little information I could get, the other company added another remote I/O panel but as it was closer to another remote I/O adapter they put the new adapter somewhere in the 'middle' of this chain. It is all connected up correctly and the new panel is also communicating but I was wondering if maybe they had got some dip switches set incorrectly which was interfering with my adapter.

Mark

MarkNightingale said:

Jimbo,

I was wondering if maybe they had got some dip switches set incorrectly which was interfering with my adapter.

Click to expand...

That could be... but I would still double-check the terminator resistors.

Jimbo,

I checked and double checked the termination resistors and even changed them because I have been bit in the a$$ before by this, and as I said as soon as I did an auto-configure everything was working again.

It was just strange because we have had the power off to these remote I/O panels before and not had to reconfigure when powered back on.

Mark