DCS system design selection issues

This post was last edited by HEJIYUER on 2020-6-14 at 20:03. Explosion protection relies on the enclosure, while intrinsically safe design depends on electronic circuits. The intrinsically safe circuit is easy to maintain. Additionally, thanks to the isolation function of the safety barrier, it can protect the cards and help to counteract signal interference. Of course, it requires an investment in safety barriers as well as additional cabinet space. For analog two-wire instruments, the vast majority have an intrinsically safe version; even those with a four-wire configuration can provide an intrinsically safe output (with a few exceptions). For DO solenoid valves, it is conventional to use explosion-proof (or encapsulated + increased safety) designs; therefore, an intrinsically safe design is not necessary. There are various signal output formats for on-site (or valve position) switches, such as passive contacts, NAMUR, PNP two-wire or three-wire systems; it’s indeed difficult to decide whether to use an intrinsically safe circuit. After all, most PNP types do not have intrinsically safe versions. 　 I agree with your approach: keep the analog signals as intrinsically safe as possible, while designing the digital signals as non-intrinsically safe. The advantage of this is that the analog signals are handled by intrinsically safe terminal cabinets, while the digital signals are handled by non-intrinsically safe terminal cabinets; this prevents misalignment of signals and cabinets, results in a simpler internal design for the cabinets, and makes management easier. This can also be considered a characteristic of China; after all, according to European principles, if an intrinsically safe system is used, it is necessary to keep everything as close as possible to the intrinsically safe circuit, with the exception of solenoids, indicator lights that require power to function, and control cabinets that have already been designed to be explosion-proof. . .