We assign the term fieldbus junction box to an enclosure mounted in a remote location, near the process, containing some type of electronic distribution module for use in a digital ‘fieldbus’ application.
The module mounted within the enclosure typically provides short-circuit protection, current limitation, isolation, and other electronic monitoring to the connected field instruments/sensors and to the control system.
In a digital fieldbus network like PROFIBUS PA or FOUNDATION fieldbus, it is very important to provide protection against inadvertent shorts or other faults. FF and PA fieldbus networks share a single shield twisted pair for power and communication, so a fault of this type could potentially affect the entire network if the individual instruments are not isolated. This is the main reason it is NOT recommended to daisy chain PA and FF devices.
Fieldbus Segment Protectors, sometimes referred to as 'Fieldbus Bricks' or 'Device Couplers', can be mounted within stainless steel, mild steel, GRP, or plastic enclosures, according to customer requirements, and located near the instruments being used to monitor process variables like temperature, pressure, level, and flow.