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poovs

Junction Box I/O Sequence (Best Practices)

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Just curious on this one... I'm coming from a discrete controls industry to fluid and gas controls... I know there isn't really a right/wrong answer here and there don't appear to be any ISA standard practices for this, but... How would you typically order/sequence your I/O terminals in field junction boxes? Groups of: Discrete Inputs + spare Discrete Outputs + spare Analog Inputs + spare Analog Outputs + spare Hart I/O + spare The initial plan is to bring everything back to the headend (PLC) via multi-conductor cabling... but grouping items in this way would allow for adopting remote/distributed I/O in the junction boxes if we later decide to... Any thoughts?

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Hi Personally, I would go straight to remote IO. Especially for your analogue IO, long multi-core cables aren't the best thing. Is there some reason you don't want to start out with remote IO? In any case, I can't see anything wrong with what you are thinking, but I don't know of any standards or preferred practices. Keep the analogue signals well away from noisy stuff and use shielded cables for them. Are you sending power down your multicore cables or using power supplies in the junction boxes - watch out for volt drop on long 24V feeds. Just my opinion. Cheers

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There really is no set standard when creating a junction box. It is important to do what makes the most logical sense for your particular application and shops. However, as Poovs said, with longer runs with analog you must be conscious of noise. If you have the opportunity a shielded cable should be used. It is important to consider how long your cable is run. Although voltage drop may be an issue, it is recommended that you don't go over a certain length of cable with analog signals.

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