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The Principle and Classification of Safety Barriers

1. What is an intrinsic safety barrier instrument?


China safety barrier is generally used in intrinsic safety systems. Intrinsic safety refers to system explosion-proof technology, which refers to the function of making production equipment or production system itself safe through design and other means, and will not cause accidents even in the case of misoperation or failure. The safety barrier is a commonly used associated equipment in intrinsic safety explosion-proof systems. The safety barrier (such as GS8500-EX and GS8597-EX.3 safety barrier from Chenzhu )is a circuit between the field equipment and the control room that limits energy.


2. The basic function of intrinsic safety barrier


To enable intrinsic safety equipment in hazardous locations to work normally, and to limit the electrical energy supplied to field instruments from the control room to a range that can neither generate sparks which are sufficient to detonate dangerous gases nor enable instrument surface temperature to be high enough to detonate dangerous gases.


As long as the current-limiting and voltage-limiting circuit of the intrinsic barrier is working properly, it will not generate any sparks or cause surface temperature to be high enough to ignite an explosive environment. Therefore, whether the control room equipment in the safe place or the intrinsic safety equipment in the dangerous place fails, the entire system will be in an essentially safe state on the circuit and will not cause an explosion.


Since the intrinsic safety barrier is designed as an energy-limiting interface between the field equipment and the control room equipment, no matter whether the control room equipment is in a normal or faulty state, the safety barrier can ensure that the energy transmitted to the field equipment through it is intrinsically safe.


3. Classification of intrinsic safety barriers


Intrinsic safety barrier, as the associated equipment between the non-intrinsic safety equipment in the control room and the intrinsic safety equipment in hazardous locations, is an important part of the intrinsic safety explosion-proof system. According to the structure, it is divided into two types: Zener safety barrier and isolation safety barrier.


(1) Zener safety barrier. In the circuit, the fast fuses, current limiting resistors and parallel voltage limiting Zener diodes are connected in series to realize the energy limitation, and to ensure that the energy is safely limited when the signals of instrument in dangerous area and the instrument in safe area are connected. It uses very few components, with advantages of small size, and low price, but there are also some fatal flaws, which greatly restrict its scope of application.


(2) Isolated  barrier. A circuit structure that electrically isolates the input, output, and power supply from each other is adopted. Like digital input barrier, it has both the energy limiting function and the isolation function, and at the same time it meets the requirements of intrinsic safety energy limiting. Isolated intrinsic barriers are mainly composed of loop energy limiting units, signal and power isolation units, and signal processing units. Its outstanding performance advantages have brought great benefits to users in applications.


Isolated  barriers have outstanding advantages and a wider range of uses. Although the price is slightly higher than the Zener safety barrier, considering the design, construction, installation, commissioning and maintenance costs, the overall cost may be lower than that of the Zener safety barrier.

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