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Instrument Safety Principle: An explosion occurs when explosive substances, oxygen, and an ignition source are all present at the same time. If we can eliminate any of the conditions that lead to an explosion, we can ensure the safety of the instruments and equipment on site. Oxygen in the air cannot be controlled; therefore, controlling explosive substances and ignition sources are the commonly used safety principles at present. In the instrumentation industry, controlling the explosion range is also considered a common safety principle. A safety barrier can limit the electrical energy of field instruments, preventing them from generating sparks that could cause an explosion or reaching temperatures on the instrument surface that could lead to an explosion. Intrinsic safety technology can eliminate potential hazards and ensure safety at the site. Classification, grading, and grouping of the hazards in hazardous areas. TITLE CONTENT: Functions and types of safety barriers. Intrinsic safety (IS) is an explosion-proof technology used in instrument systems; safety barriers are placed between the equipment in the control room located in safe areas and the intrinsically safe equipment in hazardous areas, to transmit signals or energy. The safety barrier uses circuitry to limit current and voltage, thereby preventing energy from being transmitted from the safe area to devices in the hazardous area. Inexplosive-proof equipment located in hazardous areas can operate properly at such levels of energy, but this energy is not sufficient to ignite an explosive environment; even if the equipment itself fails, no electric sparks or hot surfaces are generated that could cause ignition. Therefore, whether it is a malfunction in the equipment in the control room in a safe area or in the intrinsically safe equipment in a hazardous area, as long as the current and voltage limiting circuits of the safety barrier function properly, the entire system will remain in a safe state and no explosion will occur. Safety barriers are divided into two categories: Zener safety barriers and isolated safety barriers. The Zener-type safety barrier was the first type of safety barrier to appear. Its core components are a Zener diode, a current-limiting resistor, and a fast-blow fuse; the schematic diagram is shown below. The schematic diagram of a Zener-type safety barrier shows that the current through the Zener diode is relatively low; however, in field applications, fluctuations in the system power supply and interference can occur, leading to equipment damage. Additionally, since an intrinsically safe grounding is required, this type of safety barrier is less commonly used in practical applications. Isolated safety barriers can not only limit voltage and current but also provide electrical isolation. The safety barrier of the isolation room is mainly composed of an energy-limiting unit, signal and power isolation units, and a signal processing unit; the basic functional circuit is shown in the figure below. Compared to the zener-type safety barrier, the schematic diagram of the isolated safety barrier shows that it offers **superior performance: ① It employs a three-way isolation approach, eliminating the need for isolated instruments ； ②Reduce the instrument requirements in hazardous areas; isolated instruments are not necessary on-site ； ③Stability and interference resistance are **enhanced during operation**, resulting in a significant improvement in the reliability of the entire system ； ④It has strong signal processing capabilities, enabling it to receive and process various types of signals, such as those from thermocouples, thermal resistors, and frequency sensors ； ⑤It provides two isolated signals for two devices connected to the same signal source; the signals from these two devices do not interfere with each other, and the electrical insulation between the connected devices is also improved. The application of safety barriers in instruments: In the petrochemical production process, it is necessary to use on-site instruments to monitor parameters such as pressure, temperature, flow rate, and liquid level, in order to ensure that production can proceed smoothly. As a safety guardian for instrument control systems, the safety barrier is required to receive and process signals from the hazardous area, and transmit safe signals processed accordingly to either the safe area or the hazardous area. Although the types of signals from field instruments vary, overall they can basically be divided into two categories: input safety barriers and output safety barriers. Input safety barriers are primarily designed based on several types of signals, including standard 4–20mA/1–5V signals, thermal resistor and thermocouple signals, digital signals, communication signals, AC signals, and other non-standard signals ； Output-type safety barriers are designed primarily based on several types of signals, such as 4–20mA/1–5V signals, digital output signals, and communication signals. In production design, analog input safety gates and analog output safety gates have been widely accepted by designers and used in engineering projects. Analog input safety gates are typically used in conjunction with 2-wire or 3-wire transmitters or 4–20mA signals, while analog output safety gates are usually used with control valves. The use of isolated safety barriers has significantly improved the stability of instrument systems. It supplies the appropriate amount of power to the field instruments and valves, and at the same time isolates and converts the 4–20mA DC current signals generated by these instruments and valves into DC current or DC voltage signals, which are then supplied back to them. Key points to note regarding the use of safety barriers in petrochemical production technologies. At present, intrinsically safe systems are regarded as design standards and are applied in various fields. In production, the selection of safety barriers must meet the requirements of the site, and the following points should also be taken into account during use in order to achieve the desired results. 01 Regarding explosion-proof safety barriers, it is necessary to meet the required explosion-proof rating for the specific installation site; this ensures the proper storage of energy in the cables and on-site equipment, thereby maintaining their capacitive and inductive functions. 02 When installing a grounded Zener safety barrier, a very reliable grounding system is required, and its grounding resistance must be less than 1 ohm. 03 Regarding instruments, select a suitable safety barrier based on the type of signal from the on-site instruments. 04 Regarding cable intrinsically safe system equipment, intrinsically safe cables must be used, and such cables should be laid separately from non-intrinsically safe cables during installation. And signs need to be made.