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Forum index » Science and Technology » Engineering » Control
Signal earthing to control system
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easy.wei@gmail.com
science forum beginner


Joined: 04 May 2006
Posts: 3

PostPosted: Wed Jul 12, 2006 3:35 am    Post subject: Signal earthing to control system Reply with quote

to combine or not to combine , this is a problem.
In one project , DCS vendor Honeywell requested that the
signal earth of DCS system should be seperated from plant electrical
earthing system. They said electrical earth maybe disturb instrument
signals to DCS. But our electrical engineer suggested that combined
earth was better and seperated earth may make system worse.
Anyone has experience of control system earthing?
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Jerry Avins
science forum Guru


Joined: 03 May 2005
Posts: 534

PostPosted: Wed Jul 12, 2006 3:54 am    Post subject: Re: Signal earthing to control system Reply with quote

easy.wei@gmail.com wrote:
Quote:
to combine or not to combine , this is a problem.
In one project , DCS vendor Honeywell requested that the
signal earth of DCS system should be seperated from plant electrical
earthing system. They said electrical earth maybe disturb instrument
signals to DCS. But our electrical engineer suggested that combined
earth was better and seperated earth may make system worse.
Anyone has experience of control system earthing?

Single-point earthing avoids ground loops (should that be earth loops? I
get dizzy thinking about that) The earthing leads should carry no
current common to the instruments and the power equipment. In sever
cases, instrument amplifiers (or isolation amplifiers) may be helpful.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
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fulliautomatix
science forum beginner


Joined: 01 May 2005
Posts: 34

PostPosted: Wed Jul 12, 2006 12:17 pm    Post subject: Re: Signal earthing to control system Reply with quote

easy.wei@gmail.com wrote:
Quote:
to combine or not to combine , this is a problem.
In one project , DCS vendor Honeywell requested that the
signal earth of DCS system should be seperated from plant electrical
earthing system. They said electrical earth maybe disturb instrument
signals to DCS. But our electrical engineer suggested that combined
earth was better and seperated earth may make system worse.
Anyone has experience of control system earthing?


Mine are always earthed to one point, and if several power supplies are
used I tie the neutrals together

But my DCS's are cobbled together expansions and bits added to machines
rather than something designed from the ground up
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