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Old October 12th, 2017, 12:38 PM   #1
nick88
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RS485 Communication Issue

I have a Redlion G315 HMI dsplay with a RS-232 serial communication link using an ABB TotalFlow Master driver. The RS-232 serial line is hooked to a B&B Smartworx RS-232/RS-485 isolated converter. 2-wire RS-485 link wired as a daisy chain is used to talk to three different nodes in the field. Total distance of communication link is probably around 600 ft or so. Im using a single pair shielded 16awg.

Each node is a Totalflow RTU. I do have the termination resistor jumper set on the last RTU. I am using the Redlion to poll app-array-registers out of the RTU's and display on the HMI.

I am able to poll the first RTU with no issue, but if I try polling the polling the second RTU, I loose communications. I do not receive any data from RTU's one or two.

What are some troubleshooting methods I can try to see whats going on?

Nick
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Old October 12th, 2017, 01:46 PM   #2
KuulKuum
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Quote:
Originally Posted by nick88 View Post
I have a Redlion G315 HMI dsplay with a RS-232 serial communication link using an ABB TotalFlow Master driver. The RS-232 serial line is hooked to a B&B Smartworx RS-232/RS-485 isolated converter. 2-wire RS-485 link wired as a daisy chain is used to talk to three different nodes in the field. Total distance of communication link is probably around 600 ft or so. Im using a single pair shielded 16awg.

Each node is a Totalflow RTU. I do have the termination resistor jumper set on the last RTU. I am using the Redlion to poll app-array-registers out of the RTU's and display on the HMI.

I am able to poll the first RTU with no issue, but if I try polling the polling the second RTU, I loose communications. I do not receive any data from RTU's one or two.

What are some troubleshooting methods I can try to see whats going on?

Nick
Nick,
Is this a new installation or an existing one that used to work?
You also stated single pair shielded 16awg (is this "twisted" pair?) also is the signal grounded to a common ground?
Another idea is to provide terminating resistors at each extreme end of your communication link.
Check you communication settings (half duplex, baud rate, parity, etc.)
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Old October 12th, 2017, 06:09 PM   #3
danw
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RS-485 does not like spurs. A spur is cabling which the tees off the main line and to connect to a node on multidrop network. Reflections will create comm issues. The main line network should connect to the node directly and then go onto the next node from the same node connection terminals.

Be aware that a lot of devices do not register or acknowledge changes in serial settings (baud rate, parity) unless the device is power cycled.

The cable should be twisted pair.

Comm cables should not run parallel to or in the same conduit/tray as power wiring.
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