A transmitter on a pipe rack and a number on an operator’s screen are connected by a chain of components: tubing, a junction box, a multicore cable, a marshalling cabinet, an I/O card, a controller and a network. Different people install each link, often weeks apart. Following control system installation along that chain, from field device to control room, shows where problems usually appear.
The signal path from field to control room
- Field instrument, such as a transmitter, switch or valve positioner, installed to its hook-up drawing
- Field cable to a junction box
- Multicore cable from the junction box to the control room or field equipment room
- Marshalling cabinet, where field wiring is cross-connected to system I/O
- System cabinet with I/O modules, controllers and power supplies
- Network to operator and engineering workstations
Remote I/O and fieldbus designs shorten parts of this chain, but the principle is the same: every connection has to be right for the signal to arrive correctly.
Field instrument installation
- Location and orientation as per the hook-up drawing, including impulse line slope for liquid or gas service
- Impulse tubing in the correct material and fittings, supported and leak tested
- Clear tagging that matches the instrument index
- In-line instruments and control valves removed or protected before line flushing and pressure testing
- Late installation where possible, to limit construction damage
Removed instruments need a tracking list. Instruments taken out for flushing and never reinstated are a familiar cause of last-minute delays.
Control room and equipment room installation
Rooms should be finished, clean and air-conditioned before system cabinets arrive. Control system electronics do not tolerate dust or heat, and in hot climates the HVAC must be running before cabinets are energized. Cabinets are then set, earthed according to the project’s instrument earthing design, connected to UPS power and networked, with fiber optic links spliced and tested.
FAT and SAT
| Test | Where | Purpose |
|---|---|---|
| FAT (factory acceptance test) | Vendor’s facility | Verifies hardware, software and configuration before shipment |
| SAT (site acceptance test) | Installed on site | Confirms the system works with site power, networks and interfaces |
Interfaces with package PLCs and third-party systems should be tested as early as possible, ideally in an integrated FAT. They are a common source of surprises.
Where installation problems show up
- I/O assignments that do not match the loop drawings
- Package equipment signals missing or wrongly scaled
- Network addressing conflicts
- Earthing errors producing noisy signals
- Instruments damaged during flushing or testing
Most of these surface during loop checking, which is why it is planned as a major activity in its own right. See pre-commissioning checks for E&I systems.
Loop folders
Each loop should have a folder containing the loop diagram, instrument datasheet, calibration certificate, installation check sheet and loop check record. These folders feed directly into the handover dossier.
Cable-side controls are covered in cable tray, cabling and termination controls, and cabinet and switchgear work in panel installation and testing.
Apex Core Engineering provides instrument and control technicians and E&I supervisors through skilled manpower supply. For the full E&I scope, see electrical and instrumentation services for process plants.
Frequently asked questions
What is a marshalling cabinet?
A cabinet where field cables are cross-connected to control system I/O, so field wiring and system wiring can be organized independently.
What is the difference between FAT and SAT?
FAT tests the control system at the vendor’s facility before shipment. SAT tests it after installation on site.
Why are field instruments installed late?
To protect them from construction damage and from flushing and pressure testing.
Plan your control system installation with Apex Core Engineering.