Regarding safety barriers
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May I ask, 1. Does the safety barrier need to be selected in the same way as instruments? Should it be configured by DCS itself? 2. Is a safety barrier only required for analog signals? Is a pressure switch necessary? Is an electromagnetic valve necessary? Is it required only when the local equipment is intrinsically safe, and for the input and output signals?
It seems like your question is a bit confusing. First of all, you need to know that the two main functions of a safety barrier are to protect the components and to limit power supply, thereby enabling intrinsically safe explosion protection in conjunction with intrinsically safe instruments. 1. The safety barrier needs to be selected; different manufacturers offer various product models. If you are a supplier of instruments, it is necessary to clarify the scope of supply, as it needs to be installed inside a cabinet. Generally, it is part of the overall DCS design and procurement process. 2. For analog signals, intrinsically safe instruments are mandatory; for the others, they can theoretically be used or not. If they are not intrinsically safe instruments, installing a signal isolation barrier is a common practice. Digital signals can also be equipped with isolation barriers, and there are products available for that purpose; however, intermediate relays are more commonly chosen. They offer similar functionality but at a lower cost.
This post was last edited by MrD_lbb99 on 2026-3-17 21:02. Assuming the instrument is installed in an explosive hazard area: 1. If the field instrument is intrinsically safe, a safety barrier must be used on the DCS’s field side to ensure that the energy supplied to the field remains within safe limits； 2. If the field instruments are intrinsically safe, a safety barrier is not required on the field side of the DCS. Intrinsic safety instruments are all relatively low-power ； If it is an intrinsically safe instrument, the safety barrier will limit the amount of energy available, which may result in the field instruments not having enough power to function properly, such as two-wire transmitters and solenoid valves.
According to the design requirements, if a safety barrier is used for the intrinsically safe circuit, safety barriers are provided for AI, AO, DI, and DO. You’re right about the latter sentence; the use of intrinsically safe, flameproof, or other explosion-proof rated instrument equipment on-site is determined based on the operating conditions and regulatory requirements. If intrinsically safe type is used, the entire circuit must be intrinsically safe, and the cables as well must be intrinsically safe.
I work in instrument design; if the DCS handles the configuration uniformly, then there’s no need to list it in the instrument list
If you say it’s not a intrinsically safe instrument, will the control system manufacturer still provide a signal isolation barrier? Regardless of the type of project?
It’s not certain; it depends on many factors. Of course, the most important ones are the project budget and the level of attention given by those in charge. In other words, it can be used even if the necessary resources aren’t available, and there’s no harm in having those resources available as well.
First of all, the intrinsically safe circuit must be equipped with a safety barrier and intrinsically safe cables； Explosion-proof instruments are equipped with isolators; motor-related signal relays are isolated as well ； Secondly, different design institutes have varying approaches when it comes to selecting safety barriers. To save time, many design institutes assign the task of handling safety barrier isolators and similar components to system integrators, without preparing separate specification documents; instead, they simply list in the IO list which signals require safety barriers and which require isolators.