On the explosion protection of thermal resistors and thermocouples
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The site is in a hydrogen IIC environment; thermoresistors and thermocouples form a intrinsically safe circuit via safety barriers to be connected to the DCS for display. Question: 1. Can ordinary thermocouples and thermal resistors be used in sites equipped with safety barriers? Is it still necessary to use thermoresistors and thermocouples that meet the IIC standard? 2. What is the basis for doing this (relevant standard number)?
I suggest the original poster check the intrinsically safe explosion-proof standard GB 3836. As far as I remember, thermocouples and thermal resistors are components that do not require intrinsically safe certification, as they already meet the intrinsically safe requirements; moreover, some safety barriers can be connected directly to thermocouple and thermal resistor components.
Instrumentation devices that generate or store electrical energy of no more than 1.2V, 0.1mA, 20μJ, and 25mW are referred to as simple instruments. Simple instruments do not require intrinsically safe certification; they can form an intrinsically safe safety circuit in combination with an intrinsically safe certified safety barrier. Common simple instruments include: ● Temperature signal input: thermocouples and thermal resistors. ● Switch signal input: dry contact, such as pressure switches, temperature switches, limit switches, buttons, etc. ● Switch signal output: LEDs, etc. Thermoresistors/thermocouples do not require intrinsically safe certification, but the wires connecting them do need such certification; likewise, safety barriers also require intrinsically safe certification in order to form an effective intrinsically safe circuit. Additionally, if it is not Zone 0, using explosion protection is also sufficient; in that case, there is no need to add a safety barrier.