There are times when you need only an intrinsic safety barrier or surge protection to get the job done. But what if you need more than just a component, something more customized, something like a complete system solution—including documentation and certification? Sure, you could always build your own and have it certified yourself. But it's time consuming, and the number of approval standards and certification bodies is enormous. You really need to be focusing on keeping your plant running.
An IS barrier (also called an intrinsic safety barrier) is, quite simply, an electronic safety device that is used to protect a circuit or instrument located in a hazardous location from becoming an ignition source.
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.
Does a field instrument need to be rated IS when it’s used with an intrinsic safety barrier?
If we make the obvious assumption that the area classification in which the field instrument is mounted is rated Class I, Division 1, the answer is YES. The instrument must be intrinsically safe if it’s connected to an intrinsic safety barrier.