Thermistor zero-current issue
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Hello everyone, I have two questions. First of all, thank you to the experts for their replies; thanks a lot. Question: 1. Can a thermoresistor be connected to a safety-rated terminal box? According to 5.3.10 of SH/T 3005-2016 regarding the selection of temperature sensing elements, k) The junction boxes for temperature sensing elements installed in explosive hazard areas should be of the flameproof (Exd) or increased safety (Exe) type ； It seems it’s not possible. But if an intrinsically safe junction box is used, along with intrinsically safe cables, and the transmitter, main cables, and safety barriers are all properly configured, would that work? Question 2: Is it feasible to use a intrinsically safe gauge head with a non-intrinsically safe cable and without a safety barrier? In my opinion, since no safety circuit has been formed for this issue, it should not work.
Question 1: According to the SH/T 3005-2016 standard, the wiring boxes for temperature sensing elements in explosive hazard areas must be of the flameproof (Exd) or increased safety (Exe) type. Even with an intrinsically safe junction box and all cables and transmitters being of the intrinsically safe type, it still does not meet the requirements of this standard. Therefore, it is recommended to use flameproof or increased safety type junction boxes. Question 2: It is not feasible to use a intrinsically safe meter head with a non-intrinsically safe cable without using a safety barrier. Such a configuration cannot ensure the intrinsic safety of the entire circuit, and safety hazards may exist. The correct approach is to ensure that the entire circuit system meets intrinsically safe requirements. .
You’re welcome! Feel free to ask me more questions if you have any! I hope my answer is helpful to you. .
The key point is that the typical data sheet for HGT20638 indicates that it is intrinsically safe. . . .
No standard requirements are specified; the junction box must be flameproof and intrinsically safe
The specifications state that the junction box should be of increased safety type or explosion-proof type; this applies to junction boxes, and there is no such thing as an intrinsically safe type for junction boxes. . Intrinsic safety refers to the electronic components inside the junction box. Thermal resistors are simple components that do not store energy; in principle, they are intrinsically safe and therefore do not require intrinsically safe certification. Safety barriers or intrinsically safe cables can be used to form an intrinsically safe circuit ； Alternatively, an explosion-proof junction box can be used; it is possible to apply it in explosive environments without the need for intrinsically safe cables and safety barriers.
Intrinsic safety refers to the electronic components inside the junction box. This does not conflict with the Zengan junction box. Clause 10.1.7 of GB 50093-2013, the Code for Construction and Quality Acceptance of Automation Instrumentation Projects, also requires that the branch wiring of intrinsically safe circuits shall be installed within enhanced explosion-proof junction boxes.
Additionally, reference can be made to SH/T 3521-2013 Technical Specifications for the Construction of Petrochemical Instrumentation Projects, 8.8.9 e): For the branches of intrinsically safe circuits, the connections should be located within enhanced safety type junction boxes；