DH+ optical isolation

TheWaterboy · Jan 18, 2017

I have a DH+ connection that runs more than a mile underground parallel to a water pipe.
Once maybe twice per year when soil conditions are just right and I get to feeling relaxed, a lightning strike miles away will induce a spike into the water pipe enough to couple to the DH+ cable (Telco wire BTW, not blue hose) and destroy the comm channel of a PLC5.

I want to optically isolate this wire on both ends, Will a 485 isolator work with this signal?

JaxGTO · Jan 18, 2017

I don't believe DH+ is DH485. But AB used to sell an optical isolator unit. Probably don't make it anymore but some place lick PLC Center might still have them.

Dravik · Jan 18, 2017

I used some of these in a previous life http://www.phoenixdigitalcorp.com/rockwell-automation.html

Ken Roach · Jan 19, 2017

I think we've talked about this one before; Transtector makes the best lightning protectors I've seen deployed on DH+/RIO systems.

TheWaterboy · Jan 19, 2017

Hi Ken, Yes we have and the Transtectors I installed have not been completely effective. Whereas the strikes used to take out both PLC's now they only take out one. That's progress I suppose, but I'd like to do better.

TheWaterboy · Jan 19, 2017

Dravik
I don't have the option to replace the cable, its direct buried.

danny.michael · Jan 19, 2017

http://www.modbus.org/images/devices/PD_OpticalCommModule.pdf
Or you might buy a couple of used 1771-AF modules.

Bit_Bucket_07 · Jan 19, 2017

TheWaterboy said:
Dravik
I don't have the option to replace the cable, its direct buried.

Use two Phoenix Digital media converters on each end. It's an expensive solution, but it would give your PLC optical isolation. Of course, then the PD equipment would be exposed to the spikes.

Unless you abandon the buried cable and replace it with fiber or wireless, something is going to take a hit.

Ken Roach · Jan 20, 2017

Another approach might be the optically-isolated converters that Weed Instrument makes. I think they're owned by Ultra Electronics now:

http://ultra-nspi.com/products/indu...000-series/electrical-interface-modules-eims/

The principal use of those modules is to convert copper to fiber and back, but you can also use them copper-to-copper and take advantage of the isolation across their data "backplane", but I'm not sure how strong that isolation is. Maybe you'd have to put a fiber link in to actually get isolation.

DH+ optical isolation

TheWaterboy

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JaxGTO

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Dravik

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Ken Roach

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TheWaterboy

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TheWaterboy

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danny.michael

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Bit_Bucket_07

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Ken Roach

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