Super Discussion (Explosion-Proof Systems and Intrinsic Safety Systems)
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There is a real-world example from a factory: the limit switch (inductive type) of a control valve is of the intrinsically safe type, and it is connected to an intrinsically safe IO card in the control room using an intrinsically safe cable. After installation, the system can run. Let’s discuss it together. First, is this a intrinsically safe circuit or an explosion-proof circuit (is there a regulatory basis for this)? Second, according to the specifications, can the circuit be designed as indicated in the instructions? Third, in response to this situation, was the design on site changed (by replacing it with flameproof IO cards to create a flameproof circuit)? Or replace it with an intrinsically safe limit switch to turn it into an intrinsically safe circuit).
From a personal perspective, explosion protection ratings all have minimum requirements; given that these minimum requirements are met, it is acceptable in my opinion to choose a higher explosion protection rating. However, the circuit can only be rated at the lowest explosion protection level (the barrel principle).
This post was last edited by wangyongan on 2011-10-27 at 11:00. Personal opinion: The explosion protection rating is a systematic concept; it has no practical meaning when applied to a single device alone. For this purpose, refer to GB3836.1\GB3836.2\GB3836.4. Due to the use of flameproof equipment, the circuit should be a flameproof circuit ； This design poses difficulties for the designer, as a detailed understanding of the device parameters is required to avoid mismatches.
Reply to 2# zzyslhj: This is mentioned in GB3836.18-2010, but it refers to intrinsically safe systems. I wonder if you have a regulatory basis for this. Check whether it meets the acceptance criteria or regulatory requirements.
Reply to 3# wangyongan: If, according to GB3836.18, the limit switch is regarded as a switch and considered a simple electrical device, it can be directly installed in an intrinsically safe circuit – and that is what an intrinsically safe circuit is. I’m not sure if what you said has any regulatory basis. Welcome to continue the discussion.
Sharing my personal opinion: Intrinsic safety and flame isolation are two methods of explosion protection. The former achieves current limitation in the electrical circuit, ensuring that a short circuit does not generate sparks; the latter relies on protective measures for the equipment. Higher standards are required for the manufacture of explosion-proof devices, which must be robust enough to prevent any sparks generated inside from posing a threat to the external environment. For this reason, explosion-proof devices need to be powered off when dealing with faults. Based on the above views, I believe it is completely acceptable to use it in this way, but it should be used as an explosion-proof circuit; that is, power must be cut off when dealing with faults.
I used to have many questions about this, and after looking at the designs of some large complexes, I came up with my own conclusions (which might be somewhat one-sided). Intrinsic safety systems mainly refer to analog signals of 4–20 mA, as well as Pt100 and pulses; instruments that involve DI/DO and power-supplied devices should be part of explosion-proof systems. Of course, DI/DO can also be used in intrinsically safe applications, but it is necessary to consider whether the power supply of the safety barrier can drive the solenoid valves (the current required for intrinsically safe operation is very low, making it difficult to drive solenoid valves). This is why in intrinsically safe systems, the DI and DO components of instruments generally do not have safety barriers; in the absence of such barriers, they must be considered as part of an explosion-proof system. Furthermore, for four-wire instruments (i.e., those with separate power supply), they are generally intrinsically safe or explosion-proof; intrinsically safe refers to the safety of the signal, while explosion-proof relates to the safety of the power supply. There are many such things. Therefore, intrinsically safe systems are generally used together with flameproof systems to form the control systems in chemical enterprises. I didn’t express myself well; feel free to give your feedback
This post was last edited by lmsa613 on 2011-10-27 at 19:34. Intrinsic safety instruments must be used in conjunction with safety barriers, and intrinsic safety cables should be employed. The function of the safety barrier is to limit the current level (apparently to <100mA)； Flameproof instruments isolate the energy source from explosive gases. If an intrinsically safe instrument is not equipped with a safety barrier, it is not an intrinsically safe circuit; imagine the consequences if such an instrument is located in an explosion-proof area. Explosion-proof instruments use intrinsically safe cables and intrinsically safe connectors; of course, it is no longer an intrinsically safe circuit (theoretically).
This post was last edited by Hariky on 2011-10-28 00:08. Reply 1# lbbs: There is no such concept as an explosion-proof circuit; only the concepts of \"inherently safe circuits\" and \"non-inherently safe circuits\" exist. Both flameproofing and intrinsically safe design are explosion protection measures. Before going into details, it is necessary to understand how explosion isolation and intrinsically safe design meet the explosion protection requirements. After that, you will find that the circuit you built earlier is a \"non-intrinsically safe circuit\", but flameproofing technology is used on the field side, satisfying the explosion protection requirements (provided there are no other issues). It is possible to make modifications; first, it is necessary to determine whether the intrinsically safe card you are referring to is of the type similar to DeltaV’s intrinsically safe cards (those with current-limiting functions and intrinsically safe certification). If so, an intrinsically safe circuit can be created by modifying the limit switch. It is also best to lay its cable together with other intrinsically safe cables.
Reply to 8# lmsa613: Does the situation I’m describing now meet the standards? Can it pass the safety inspection? Are there any review criteria?
Reply 9# Hariky: Normally, if it’s not an intrinsically safe circuit, then it’s a non-intrinsically safe circuit. Now it would be possible to prove whether it is a safety circuit. I estimate that this circuit is a intrinsically safe circuit (but I’m not sure). Firstly, an intrinsically safe circuit refers to simple electrical devices in which \"all electrical parameter values do not exceed 1.2V.\"