Allen Bradley connection issue

sjanes9 · Dec 10, 2015

We are having an odd issue with an Allen Bradley 1747-L531 processor. When we try and connect with the controller using a 1747-AIC Link coupler that connects to the PLC and a 1747-UIC Coupler to connect the computer to the Link coupler. We are using a Windows 7 64 bit computer, though it isn't relevant to the issue. Whenever the RS485 cable is connected to the link coupler, still not connected the computer. It causes our Scrap conveyor system to go into Auto shutdown mode. There are no faults appearing on the PLC. I can connect to the PLC and view the live code fine. the only way to fix it is to remove the cable from the link coupler and move the PLC key from remote to program to run and back to remote mode.
It seems like it's resetting a fault, but as I said. I don't see any faults on the PLC when I go online with it. Any help would be appreciated.

gclshortt · Dec 10, 2015

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1747-um011_-en-p.pdf
Verify proper power supply selection and backplane loading. (The 1747-PIC and 1747-AIC interface draw power off the backplane.)
Powering the Link Coupler
The 1747-AIC interface requires 85 mA at 24V dc. With a peripheral device connected, the total current required is 190 mA at 24V dc.

Regards,

Ken Roach · Dec 10, 2015

It might be a combination of power loading and a programming or network condition.

When not plugged into a computer via the USB connector, the 1747-UIC will draw power from the DH485 cable side, which is causing the 1747-AIC isolator to shut down. This is a known issue with combining these two devices in this specific configuration, documented in RA Knowledgebase article 64829 (TechConnect required).

If the USB side of the 1747-UIC is connected to a PC before plugging it into the 1747-AIC, this condition should not occur.

As to why the logic controller goes into an apparent fault mode... that's harder to say. If it was actually faulted, you should see a flashing red LED and see the fault indication when online.

What might be going on is that the SLC has program logic that checks the integrity of the DH485 network and stops the machine if it's not working. Maybe the Run/Prog/Run keyswitch cycle clears that logic.

The simple workaround is just to not plug the 1747-UIC into the DH485 network until it's plugged into a PC for power.

Geospark · Dec 10, 2015

I remember posting this some time back...

Geospark said:
...The DH-485 network would crash around 7pm every evening when turning off the laptop and wrapping up to go back to the hotel. After plugging everything out and getting the nodes back up one at a time, the network would crash again within minutes? I eventually realized that my 1747-UIC was still plugged into the DH-485 port of the 1747-AIC Link Coupler at one of the nodes that I was using to connect to the network. Even though the USB lead was plugged out of my laptop and the UIC was dead, the network didn't like something inside it when not powered up. I unplugged it and the network recovered. I went to another AIC at another node and plugged in the dead UIC and it pulled it down again! I had three UIC's to hand and tried them all, they all did the same thing. That's why it was happening every evening as I was packing up. I now had to plug out the cable from the AIC while the UIC was still powered on from the laptop before unplugging the USB lead.

It may just happen when connected to AIC Link Couplers, not sure. I'm assuming there must be an impedance in the UIC while it's powered off that pulls the network down? I would have thought there are UIC's left connected, while dead, to DH networks all over the globe? Could this possibly affect all DH networks? Maybe someone else could try if they have a similar network to hand?

That Knowledgebase article answers that query.

Thanks Ken!

Regards,
George

sjanes9 · Dec 10, 2015

Thank you guys! That was exactly the problem.

Allen Bradley connection issue

sjanes9

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gclshortt

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Ken Roach

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Geospark

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sjanes9

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