Chemical process instruments

It is known that a safety barrier, also referred to as a safety energy limiter, serves primarily to limit current and voltage, ensuring that the energy available to the instruments on site remains within safe limits.

A safety barrier is a device installed in a safe area and containing intrinsically safe circuits as well as non-intrinsically safe circuits. In these circuits, current-limiting and voltage-limiting components are used to restrict the amount of energy sent to the intrinsically safe circuits on site, thereby preventing dangerous energy from the non-intrinsically safe circuits from entering those intrinsically safe circuits. In intrinsically safe explosion-proof systems, it is referred to as a associated device and constitutes an important part of the intrinsically safe system. For example, the DCS cabinets are located in the control room, and the signals from the field instruments are sent to that control room. If the voltage from the DCS in the control room is transmitted to the field, it could pose a danger. To avoid such situations, it is necessary to isolate the DCS from the field, and that’s why safety barriers are used. It is worth noting, however, that only intrinsically safe instruments require a safety barrier. Hehe, actually, the poster should post this in the dashboard area. I came to this section to take a look, see the answers, hoping it will be clear~~

　　　　 　　Working principle of isolated safety barriers: The main function of a safety barrier is to prevent dangerous energy from entering hazardous areas, as well as to limit the voltage and current that are sent to such areas. The Zener diode is used to limit voltage. When the loop voltage approaches the safe voltage limit, the Zener diode conducts, ensuring that the voltage across it remains below this safe limit at all times. The resistor R is used to limit the current. When the voltage is limited, by appropriately selecting the resistance value, the circuit current can be kept below a safe current-limiting value. 　　Compared to Zener safety barriers, isolated safety barriers not only provide voltage and current limiting but also offer current isolation functionality. An isolation barrier usually consists of three components: a circuit power-limiting unit, a current isolation unit, and a signal processing unit. The basic functional circuit is shown in Figure 2. The loop current limiting unit is the core component of the safety barrier. In addition, the auxiliary unit includes a circuit supply circuit for driving field instruments and a detection circuit for collecting instrument signals. The signal processing unit performs signal processing in accordance with the functional requirements of the safety barrier. 　　Industrial sites generally require distributors that use a two-wire transmission system; such distributors are needed to supply 24V power to primary instruments such as pressure transmitters, and at the same time to acquire, amplify, process the incoming current signals, and eliminate interference, before outputting isolated current and voltage signals for use by subsequent secondary instruments or other devices. However, some special industrial installations require not only two-wire transmission that provides both power supply and signal isolation, but also explosion-proof properties of the safety spark type to reliably prevent contact between high voltage from the power supply and the signals. These installations need special-purpose distributors known as safety barriers, which utilize dual control of current and voltage to limit the energy entering hazardous areas to levels below safe thresholds. 　　Isolated safety barriers mainly come in two types: detection-side safety barriers and operation-side safety barriers. The detection-side safety barrier is used in conjunction with two-wire transmitters ； The operational safety barrier is used in conjunction with electrical converters or electrical valves. There are also isolated safety barriers of types such as signal input. 　　Thanks to measures such as voltage and current limiting as well as isolation employed by the isolated safety barrier, it not only prevents dangerous energy from entering the hazardous area through the intrinsically safe terminals, thereby enhancing the system’s intrinsically safe explosion-proof properties, but also improves the system’s resistance to interference, **increasing the reliability of its operation. The 24VDC power supply, after undergoing DC-AC-DC conversion, outputs various voltages required by the module circuit. 　　The principle of the isolated safety barrier at the detection end is as follows: The modular circuit converts the current or voltage signals input through the intrinsically safe energy limiting circuit into values between 0.2 and 1 VDC. These signals are then fed into the module where they are collected, amplified, processed to reduce interference, and subsequently transformed by a transformer into isolated current and voltage signals that can be used by subsequent secondary instruments or other devices. The module must also output a isolated 18.5∽28.5VDC voltage, which is used via an intrinsically safe energy limiting circuit as the operating voltage for two-wire transmitters. The intrinsically safe energy limiting circuit can prevent dangerous signals with high current or high voltage from entering hazardous areas. 　　The principle of the isolated safety barrier at the control side is to isolate the 4-20mA DC signal generated by the regulator or operator, and then output another 4-20mA DC signal, which is supplied via an intrinsically safe energy limitation circuit to the electrical converter or the on-site electrical valve positioner.

Thank you, OP. I’m a beginner looking for this kind of information to learn*

Thank you, OP; I was about to ask the same thing

I’ve learned something. . . . . . . . . . . . . . . . . . . . . .

A safety barrier is also known as a safety keeper. A safe interface for intrinsically safe circuits, which enables two-way transmission of electrical signals between the safe area and the hazardous area, and can prevent the transfer of energy from the safe area to the hazardous area in the event of a fault. Common safety barriers include Zener-type and isolation-type ones. Between intrinsically safe circuits and non-intrinsically safe circuits. A device that limits the voltage or current supplied to intrinsically safe circuits within a certain safe range.

A safety barrier is also known as a safety keeper. A safe interface for intrinsically safe circuits, which enables two-way transmission of electrical signals between the safe area and the hazardous area, and can prevent the transfer of energy from the safe area to the hazardous area in the event of a fault. Common safety barriers include Zener-type and isolation-type ones. Between intrinsically safe circuits and non-intrinsically safe circuits. A device that limits the voltage or current supplied to intrinsically safe circuits within a certain safe range.