How does a safety barrier prevent explosions?
Thread Content
How does a safety barrier prevent explosions? In China, intrinsically safe systems are attracting increasing attention, and the safety barriers that serve as their key components are also becoming well-known. So, how does a safety barrier prevent explosions? Control energy – controlling energy is the key to ensuring the explosion protection of safety barriers. Whether it is a Zener safety barrier or a isolated safety barrier, both achieve the requirements set for explosion protection by controlling energy. A Zener safety barrier – as its name suggests – has the Zener diode, also known as a voltage-regulating diode, as its main component. But a Zener diode can only control the voltage value; then what component controls the current, which is the second element of electrical energy? The resistor, which has a certain capacity to handle power, serves as a current limiter here; it ensures that the current flowing from the safety barrier into the hazardous area remains within an allowable range, thereby achieving intrinsically safe conditions. So, how does the isolation barrier control energy? The pulse transformer is the main component used to isolate energy in safety barriers; it is thanks to this component that the energy flowing into hazardous areas can be controlled. What should I pay attention to when using a safety barrier? In addition to selecting an appropriate safety barrier, several factors need to be taken into account when using intrinsically safe systems. First, attention must be paid to the capacitive and inductive reactances of the cables and field devices. Since intrinsically safe design is a form of explosion protection for the system, it is not only necessary for the safety barrier to meet the required explosion protection standards; the energy storage capacity of the cables and field devices is also a key factor. Especially after the replacement of parameter authentication with system authentication, contractors need to pay particular attention to this issue. Secondly, attention should be paid to intrinsically safe grounding; Zener safety barriers require intrinsically safe grounding, with the grounding resistance should be less than 1. Third, intrinsically safe cables and non-intrinsically safe cables should be installed separately in different cable trays. And it should have clear markings. Fourth, be sure to turn off the power when replacing it. Should I use a isolation barrier or a Zener barrier? Generally speaking, Zener safety barriers are easy to select, not prone to damage, require few changes to the original system structure, and have obvious advantages. The explosion-proof principle of the Zener safety barrier is to use Zener diodes to control the output voltage and resistors to limit the output current, resulting in a relatively simple circuit. During normal operation, the Zener safety barrier functions as two resistors connected in series in the circuit, so no changes to the system architecture are required. Furthermore, due to the absence of signal transitions, the Zener safety barrier also has no impact on the accuracy of the original signal. The isolation safety barrier uses high frequency as the fundamental wave to modulate and demodulate the signal; any changes in the signal will affect the accuracy due to the effects of the safety barrier circuit. Isolation safety barriers generate radio frequency interference due to their high-frequency oscillation circuits, which is detrimental to the system; moreover, such barriers are also prone to damage. However, the isolation safety barrier does not require an intrinsically safe ground, which is what gives it an advantage over Zener safety barriers. In terms of price, Zener safety barriers are much cheaper than isolated ones; this price advantage of Zener safety barriers becomes evident in situations where a large number of safety barriers are required.
Most safety barriers these days seem to be of the isolated type, while previously those using Zener diodes were more common.
Our factory has both types, but in terms of performance, I think the isolated safety barrier is superior. From the perspective of ease of installation and use, it’s obviously the Zener gate.
Safety barriers come in isolated safety barriers and Zener safety barriers. The Zener safety barrier makes use of the reverse breakdown property of Zener diodes; when the voltage on the control room side exceeds a certain value, the Zener diode breaks down, causing a short circuit in the circuit and thereby preventing high voltages from the control room from reaching the field. Isolated safety barriers achieve voltage isolation through isolation transformers.
Well said; I am looking for information on these aspects.
What is an explosion-proof safety barrier?
Safety barriers achieve explosion protection by limiting energy, preventing energy from non-intrinsic circuits from entering intrinsic circuits; their internal structure actually consists of fuses, current-limiting resistors, and diodes.
Zener-type safety barriers use fast fuses, current-limiting resistors, or voltage-limiting diodes in the circuit to restrict the amount of electrical energy entering, thereby ensuring that the amount of energy delivered to the hazardous area is controlled. Its principle is simple, its circuit implementation is easy, and its cost is low. However, due to flaws in its underlying principle, its reliability in practical applications is greatly affected, which limits its scope of use. The reasons are as follows: 1. The installation location must have a very reliable grounding system, and the grounding resistance of this Zener-type 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 actual engineering applications. 2. The field instruments located in hazardous areas must be isolated-type; otherwise, when the grounding terminals of the Zener safety barrier are connected to the ground, the signals cannot be transmitted properly. 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. 4. Since the circuit principle of the Zener safety barrier requires it to absorb energy from the input circuit, it is prone to cause instability in the output. Isolated safety barrier: It employs a circuit structure that provides electrical isolation between the input, output, and power supply, while also meeting the energy limitation requirements of intrinsically safe systems. Compared to Zener-based safety solutions, although it is more expensive, its superior performance advantages bring greater benefits to users: 1. Thanks to the three-way isolation mechanism, no system grounding wire is required, which greatly simplifies design and on-site installation. 2. The requirements for instruments in hazardous areas are significantly reduced, and isolated instruments are not necessary on-site. 3. Since the signal lines do not require a common ground, the stability and interference resistance of the signals in the detection and control circuits are **enhanced**, thereby improving the reliability of the entire system. 4. Isolated safety barriers possess stronger input signal processing capabilities; they can receive and process signals from thermocouples, thermal resistors, frequencies, etc., something that zener safety barriers are unable to do. 5. The isolated safety barrier can output two mutually isolated signals, which are provided for two devices that use the same signal source, ensuring that the signals from these two devices do not interfere with each other. It also enhances the electrical safety isolation between the connected devices.
Advantages of isolated applications: ① Compared to Zener safety barriers, isolated safety barriers are more expensive, but their numerous advantages and features bring significant convenience to users, which is why an increasing number of users prefer to use isolated safety barriers. ②By using an isolated safety barrier, the field circuit signals from the hazardous area and the circuit signals from the safe area can be effectively separated. In this way, the intrinsically safe control system does not require an intrinsically safe grounding system, simplifying the construction process when applying the intrinsically safe explosion-proof system. ③ By using isolated safety barriers, **the interference resistance of the detection and control circuits is enhanced, improving the reliability of the system. ④Isolated safety barriers are used, allowing the field instruments to be grounded and enabling them to be non-isolated. ⑤ Isolated safety barriers have numerous protection circuits, which reduce the likelihood of accidental damage; they allow for maintenance of field instruments while they are still powered, thereby shortening the time required to get the plant up and running and reducing downtime. ⑥Isolated safety barriers have strong signal processing capabilities. Such as digital input status control, converting mV and Pt100 to 4–20mA, and so on. This provides greater convenience, rationality, and efficiency for the use of field instruments and control systems. ⑦ When users use both DCS and ESD simultaneously, selecting a one-input two-output safety barrier can effectively isolate the two systems from each other, preventing interference between them. ⑧The loop-powered isolated safety barrier retains the advantages of active isolated safety barriers, while also offering the easy wiring characteristic of Zener safety barriers; it does not require an additional 24V power supply, making it particularly suitable for DCS systems that are powered directly by I/O cards.