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What is the Secret to Making an AB DHRIO Work?

04/14/2015 6:16 AM

I tested a spare PLC5 with a 1756 DHRIO in a rack next to a 1756 ENBT Ethernet module and it worked perfectly. Then I mounted the 1756 rack in a cabinet near the target PLC5 and connected to an existing DH+ line with a lot of spare bandwidth.

Now, it is about 95% accurate with some of the faulty data being zero all of the time, mostly in the same bit location (bit #7 of 16) and bit #6 is bouncing when it should be steady.

Moving my line to another DH+ line with very little bandwidth available results in a lot of mixed data that dropped to about 67% accuracy. So, I'm feeling a little bit perplexed. For the cost of this module, one would expect it to work better than it seems to work.

I've been told by outside contractors that "you just have to play around with loading resistors until it works." And the literature makes promises that the reality just doesn't match. I just want to know how to make this expensive POS work without bringing the network down. Got any ideas?

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Pathfinder Tags: AB Data Highway DH+ DHRIO
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#1

Re: What is the Secret to Making an AB DHRIO Work?

04/14/2015 6:22 AM

Only one. Pick up the phone and talk to the POS supplier directly. It is by far a quicker route to the solution than waiting for responses here.

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#7
In reply to #1

Re: What is the Secret to Making an AB DHRIO Work?

04/20/2015 12:56 PM

Actually the supplier is slower. AB distributors seem to give priority and discounts to panel builders first. The rest of us only get leftovers, and only if the supplier is in the mood.

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#2

Re: What is the Secret to Making an AB DHRIO Work?

04/14/2015 11:28 AM

I got only one.....make sure that the DH+ link is terminated properly...

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#3
In reply to #2

Re: What is the Secret to Making an AB DHRIO Work?

04/15/2015 12:54 AM

Per page 23 here (manual) for example?

Maybe it's these resistors that need messing with and are not the same in the test and inservice setups....

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#4
In reply to #3

Re: What is the Secret to Making an AB DHRIO Work?

04/15/2015 3:46 AM

Well, a simple phone call to the supplier would remove all doubt!

Sheesh!

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#5
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Re: What is the Secret to Making an AB DHRIO Work?

04/15/2015 6:29 AM

There are suppliers and there are suppliers....

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#6
In reply to #3

Re: What is the Secret to Making an AB DHRIO Work?

04/15/2015 11:10 AM

The resistor (or resistors), needs to be sized according to all the variable parameters....Line type used, length of run, there should be a way to calculate this, but trial and error may yield results faster than locating some chart of resistance....

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#8
In reply to #3

Re: What is the Secret to Making an AB DHRIO Work?

04/20/2015 1:05 PM

Careful reading of the AB DHRIO manual, Publication 1756-UM514B-EN-P has a disclaimer under an "Important" note that says, "...your 1756-DHRIO module does not support bridging CIP I/O data from ....".

Enough said! It simply does not do what the salesman said it would. Imagine that!

The data that it does support, depending on its mood, is less than reliable.

I'm giving the 1756 DHRIO bridge module a big thumbs down!

I think I could build a better bridge with a few paper clips, a shoe lace and some gum.

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