Dust explosion-proof instrument signal issues
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The instrument’s explosion-proof certificate shows two certification marks: E*a IIB T4/Ex tD A21 T=135℃. This instrument is intended for use in dust-explosion hazardous area 21; can the signal type be considered as intrinsically safe?
The intrinsically safe rating for dust is actually the same as that in gas environments; therefore, with the E*aIIBT4 rating mentioned earlier, it can be assumed that an ia rating is also achievable in dusty conditions, provided that the requirements for intrinsically safe circuits are met. But in fact, this latter certification allows it to be treated not as an intrinsically safe signal in dusty environments, since other explosion-proof designs already exist; it depends on how you decide to use it.
Why can the same instrument signal be considered both an intrinsically safe signal and a non-intrinsically safe signal?
It’s not about determining what type of signal it is. Take another close look at the description; if it is implemented in accordance with the requirements for intrinsically safe circuits, this signal can meet the intrinsically safe standards. However, thanks to other explosion-proof measures, even with normal wiring, this signal may not meet the intrinsically safe requirements; yet the entire instrument still satisfies the explosion-proof requirements.