Wiring of on-site instruments
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Are the field instruments connected directly to the DCS cabinet room via instrument cables, or are cabinets installed on-site with the cables going from those cabinets to the DCS cabinet room?
For generally standardized installations, an intermediate junction box is added on-site; there is no need to install an intermediate cabinet on-site. Designed by unit, designed by region, designed for signals of the same type. Flammable and toxic gases are generally drawn directly to the cabinet room.
There are those with direct connections from the field instruments to the DCS cabinet, as well as those that have intermediate junction boxes at the field site; the cables from the field instruments go into these junction boxes, and from there they proceed to the cabinet.
It mainly depends on whether the owner prefers to add a junction box in the middle or to run the wires directly； Additionally, consider the distance between the field instruments and the cabinet room; for those that are close, direct wiring is sufficient, while for those that are farther away, it is advisable to install a junction box in between along with spare cables to facilitate maintenance in the future.
This is an issue related to investment. The advantage of using multiple cable pairs is that it is cheaper when converted into a single signal cable, there are fewer trunking boxes, fewer cables entering the cabinet, and thus construction costs are reduced. (It will also be convenient to add more signals in the future.) However, this requires additional field wiring boxes and connector fittings, which means extra costs. If comparing just a single investment, taking 12 pairs of main cables as an example, using fewer than 6 pairs is still cheaper.
I’m not a big shot; I just have a bit of experience.
Specifically, it depends on factors such as the scale of the project, the design of its units and areas, as well as explosion-proof requirements; understanding the drawings is sufficient
We use direct drawing for all of these, in order to reduce failure points