I would like to ask fellow sailors about the regulations regarding the use of safety barriers.

Where explosion protection is required, safety barriers must be used. The function of a safety barrier is to limit the voltage and current at the field level; for two-wire instruments, a safety barrier must be used to supply power so that the instrument can operate properly. For explosion protection, simply using a safety barrier is not enough; it is also required that the inductance and capacitance of the cables be below specified values. Whether to use a safety barrier depends entirely on the explosion-proof specifications chosen for the site. If the field instrument is intrinsically safe (ia), a corresponding safety barrier must be used. The model of the corresponding safety barrier can be found on the explosion-proof certificate issued for the field instrument. Explosion-proof instruments do not require a safety barrier. The explosion protection standards for instruments abroad differ from those in China; you can consult the Chemical Explosion Protection Institute in Tianjin. The safety barrier is a key instrument that ensures the process control system has explosion-proof properties against safe sparks; it must be installed in the control room and serves as a device that connects the instruments and devices in the control room with those on-site. On one hand, it functions to transmit signals ； On the other hand, it is also used to limit the energy flowing into hazardous areas.

The safety barrier was originally an auxiliary unit of electric combination instruments, and its main purpose was to serve as an isolation device in explosion-proof systems. The safety barrier transmits the signals from the hazardous area through isolation, outputting isolated current signals to the safe area. It is used in intrinsically safe explosion-proof systems, where current-limiting and voltage-limiting circuits are employed to restrict the energy sent to the field circuit, thereby preventing dangerous energy from non-intrinsically safe circuits from entering the intrinsically safe circuits. Common safety barriers can be classified into Zener-type and isolation-type based on their structural design. Applications of Zener-type safety barriers and some points to note: Fast fuses, current-limiting resistors, or voltage-limiting diodes are used in the circuit to restrict the electrical energy input, thereby ensuring that the amount of energy delivered to the hazardous area is controlled. 　　1. The installation location must have a highly reliable grounding system; the grounding resistance of this Zener safety barrier must be less than 1Ω. Otherwise, it loses its explosion-proof safety capabilities. Clearly, such requirements are quite stringent and difficult to meet in practical applications. 　　2. The field instruments in hazardous areas must be of the isolated type; otherwise, when connected to the ground through the grounding terminal of the Zener safety barrier, the signals cannot be transmitted correctly. Moreover, grounding the signals reduces their resistance to interference, thereby affecting the stability of the system. 　　3. Zener safety barriers have a significant impact on the power supply, and they are also prone to damage due to fluctuations in the power supply. Points to note when using isolated safety barriers: Adopt a circuit structure that provides electrical isolation between the input, output, and power supply, while also meeting the energy limitation requirements for intrinsically safe systems. 　　1. A three-party isolation method is adopted, eliminating the need for system grounding wires, which greatly simplifies design and on-site construction. 　　2. Isolated instruments are not required for the field instruments in hazardous areas. 　　3. The signal lines do not require a common ground, which **improves** the stability and interference resistance of the signals in the detection and control circuits, thereby enhancing the reliability of the entire system. 　　4. Isolated safety barriers possess stronger input signal processing capabilities; they can accept and process signals from thermocouples, thermal resistors, frequencies, etc., something that zener safety barriers cannot do. 　　5. An isolated safety barrier can output two mutually isolated signals, which are provided for two devices that use the same signal source; this ensures that the signals from the two devices do not interfere with each other, while also enhancing the electrical insulation between the connected devices. 　　Therefore, by comparing the characteristics and performance of Zener-type and isolated safety barriers, it can be seen that the isolated safety barrier has significant advantages and a wider range of applications; in engineering sites with high requirements, it is almost always used as the primary intrinsically safe explosion-proof instrument, and it has gradually replaced the Zener-type safety barrier

Thank you all, but it’s not quite certain yet.

Intrinsic safety refers to the fact that, under normal or abnormal conditions, the instrument does not pose a risk of explosion. Therefore, it is necessary to use safety barriers to limit the amount of sparks generated in the instrument’s circuit. Flameproofing, on the other hand, relies on the structure of the instrument’s enclosure to prevent explosions from occurring inside the instrument, thus avoiding any explosion in the surrounding area; in other words, the explosion is contained within the instrument itself. Hence, safety barriers are not required.

I’m a bit confused too. Explosion protection is designed for instruments; when an explosive gas fills the instrument, any ignition source can cause an explosion inside. The enclosure is capable of withstanding the explosive pressure from this internal mixture and preventing the explosion from spreading to the surrounding explosive gases. But how can the enclosure prevent energy from entering the control room via wires and cables?