The safety barrier, also known as the safety factor meter, is an important part of the intrinsic safety system.
There are two main types of barriers: P+F Zener barriers and P+f isolated barriers. The core elements of a double Forgina barrier are a diode, a current-limiting resistor and a fast fuse.
The safety gate signal with P+f isolation is composed of a power isolation unit and a signal processor. The main function of the barrier is current and voltage limiting to ensure that the field instrument can obtain energy within a safe range. The barrier is an energy-limiting circuit between the field device and the control room equipment, which limits the electrical energy supplied to the field instrument from the control room so that it does not generate a spark sufficient to detonate the hazardous gas, nor does it generate a meter surface temperature sufficient to detonate the hazardous gas, thus eliminating the source of the detonation. When selecting a safety barrier, it is necessary to consider the compatibility of the model with the type of field instrument, as well as the compatibility of the impedance of the safety barrier with the requirements of the basic safety instrument, as well as the impedance matching of the intrinsically safe system.
Cables and field equipment should pay attention to their capacitive and inductive reactance, intrinsically safe explosion-proof system is an explosion-proof system, in addition to the explosion-proof fence must meet the required explosion-proof level, the energy storage of cables and field equipment is also a key issue. Especially after the parametric certification substitution system certification, engineering companies should pay more attention to this issue.
In order to pay attention to the problem of grounding, the Zener safety barrier needs to be intrinsically safely grounded to the ground, and the grounding resistance should be less than 1.
Intrinsically safe and non-intrinsically safe cables should be laid separately in separate trunkings. And it should be clearly marked.
Pay attention to power failure when replacing.
Precautions for installation of P+F safety barrier:
The safety barrier should be installed in a safe place, and its environmental conditions meet the conditions of use in the "Selection of Safety Barriers".
The wiring conductors of the intrinsically safe end (blue terminal) of the isolated barrier and the non-intrinsically safe end of the circuit should be laid separately in the wiring duct and protected by a separate protective sleeve. It is not allowed to install other power cords in the wiring lines on the intrinsically safe side, including power cords for intrinsically safe circuits.
The conductor leading to the dangerous location should be an intrinsically safe wire with a blue mark, the soft copper area should be greater than 0.5mm2, and the dielectric strength should be greater than 500V.
Before the isolation barrier is energized and commissioned, it is necessary to pay attention to whether its model, wiring method, wire pole, etc. meet the design and product requirements, otherwise it will cause injury to people and equipment. The following points should be paid attention to when the isolated safety barrier is energized and commissioned.
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