Regarding the explosion-proof type of field instruments

The instruments you mentioned should all be powered by 220V AC. If an instrument fails and generates a large amount of spark energy, it is not intrinsically safe; therefore, it can only be designed as an explosion-proof type

I’m not very good at this either; it’s a good opportunity to learn it by the way*.

So, for a four-wire instrument powered by 24VDC, can it be made intrinsically safe?

So, for a four-wire instrument powered by 24VDC, can it be made intrinsically safe? Which expert can offer some guidance?

Meters that require separate power supply, whether at 220V or 24V, indicate a high power consumption, which makes it difficult to design them in a cost-effective and explosion-proof format. Two-wire instruments can achieve intrinsically safe explosion protection because they use low-power electronic components.

What the brother on the 6th floor said is absolutely correct; I’ve always thought the same way. But I’ve noticed that many four-wire instruments powered by 24VDC can also be made intrinsically safe, which confuses me. Can a 24VDC power supply also be made intrinsically safe?

A 24VDC power supply can indeed be made intrinsically safe.

“A 24VDC power supply can indeed be made intrinsically safe. ”Could the brother upstairs give a specific example?

“A 24VDC power supply can indeed be made intrinsically safe. ”Could the brother upstairs give a specific example?

We imported an ultrasonic level gauge that was required to be explosion-proof and operate on a 2-wire system; however, what was delivered was a 4-wire model that wasn’t explosion-proof either

“A 24VDC power supply can indeed be made intrinsically safe. ”Could the brother upstairs give a specific example?

You can find out by checking the safety barrier or intrinsically safe power supply samples. This post was last edited by spccjp on 2009-2-22 21:42]

What was said on the 6th floor is correct, but it can’t be said that instruments with a four-wire system can’t be made explosion-proof, right? Has anyone in the factory seen four-wire intrinsically safe explosion-proof instruments?

First of all, it is necessary to understand how the safety barrier in an intrinsically safe system prevents explosions: controlling energy is what makes it safe, and this is the key to the functionality of the safety barrier. Intrinsic safety circuits limit the energy supplied to the intrinsic safety loop at the field level through current-limiting and voltage-limiting circuits, thereby preventing dangerous energy from non-intrinsic safety circuits from entering the intrinsic safety circuit. The power supply for the instrument is limited to either 220VAC or 24VDC, with the signal being 4~20mADC. If a safety barrier is used to limit the power supply energy to a level sufficient to prevent the generation of dangerous sparks, then it remains a question whether this reduced energy level will still be sufficient to ensure the proper operation of the instrument. I think it is possible to make 24VDC four-limiting instruments intrinsically safe, while it is difficult to do the same for 220VAC four-limiting instruments. This is my theoretical analysis; as for whether this can be achieved in practice, it depends on whether the instrument manufacturers are able to produce instruments that meet the technical requirements for certification as intrinsically safe explosion-proof instrument systems.

Are all field instruments that require separate power supply (i.e., the so-called four-wire instruments such as fork-type level switches, electromagnetic flowmeters, capacitive level gauges, mass flowmeters, etc.) unable to be designed in intrinsically safe and explosion-proof versions, and can only be made in flameproof versions? Because it’s impossible to make the power supply part of four-wire instruments intrinsically safe, is that correct? Also, are there explosion-proof versions of proximity switches? Not all four-wire instruments cannot be made intrinsically safe. Intrinsic safety instruments have the highest explosion protection rating; they achieve this protection by using safety barriers to limit the supply of power. Therefore, as long as a four-wire instrument has low power consumption, it can also be made intrinsically safe. There are many intrinsically safe proximity switches, while isolated types are rare.