4-20 mA over 2 km

Hello; Do you think it is possible to carry 4-20 mA on a 2 km cable without any loss. Or what can you suggest to make it possible(repeaters...)
Thanks in advance;
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Current loop wire resistance over that distance would need to be considered, wrt driving voltage.

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Yes, it can be done, especially with an adequate wire gauge. The real problem is interference.
1 - make absolutely certain the XT end is ungrounded.
2 - make certain you have a surge arrestor.
3 - Make absolutely certain you are using twisted, shielded pairs. This may be difficult with the heavier gauges.
4 - Do NOT run parallel to any power lines. Fortunately this is an inverse cube relationship so even small increases yield large improvements.
Repeaters are neither necessary nor helpful. They will not help against interference problems. Understand that there is no signal loss with a 4-20 mA loop. That is why we use them.
Walter.

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Walter Driedger wrote:

Just out of curiosity, is it worthwhile to use digital communications vs. current loop, or even fiber? You obviously know how to make this work, but is it the recommended approach for new installations?
--

Tim Wescott
Wescott Design Services
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Tim,
It depends on a lot of things. I just answered the question as asked.
When I'm faced with a situation of an analog measurement located 2 km from the control room I first ask how many more of these there are before I start laying wire for one only. These days there seems to be a lot more fibre. On the thread concerning control network security I mentioned a current situation where internet was the way to send four signals only 1 km. (Different plants, different owners, different control systems.)
Walter.

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Other considerations like how many channels, update speed, type of data, route and route cost for a few need to be considered. At some point something like fiberoptics, MW, RF, or laser maybe more practical with less interference, even though converter maybe needed at both ends.
WiFi with directional hi gain antenna's should also work and longer range standard out before too long.
Lots of things we need to know to consider, for a better answer.

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