The instruments on-site are explosion-proof; is an isolated safety barrier also needed on the DCS?

It can be determined based on the actual conditions on site; if there are flammable or explosive substances near the instruments at a certain location, a safety barrier must be installed. Either Zener or isolated types are acceptable; the isolated type is recommended. Conversely, there is no need to install a safety barrier. For example, if the environment near a workstation used to measure dynamic wind is dynamic wind itself, these points can be connected directly to the DCS cards without going through a safety barrier.

Check whether the explosion-proof type of your instrument is flameproof or intrinsically safe; an intrinsically safe instrument requires a safety barrier, while a flameproof instrument does not need one.

The explosion-proof type of the instrument is either intrinsically safe or flameproof; an intrinsically safe type requires a safety barrier, while a flameproof type does not need one.

In your case, there is no need to use a safety barrier. A safety barrier is only required on the DCS side when intrinsically safe instruments are used on-site. Whether a safety barrier is used or not has no impact on the measurement. It depends on whether the safety conditions at the site require the use of intrinsically safe instruments; if such instruments are required, a safety barrier must be used in conjunction with them.

Agree with the points in floors 3, 4, and 5; they make sense!

Explosion-proof instruments are divided into intrinsically safe and flameproof types; they need to be integrated with subsequent systems in order to truly achieve explosion protection

The explosion-proof type of the instrument is either flameproof or intrinsically safe; flameproof instruments do not require a safety barrier, while those that are intrinsically safe must have one. Safety barriers can be of the Zener type or the isolation type, and when using a Zener barrier, it is necessary to ensure proper intrinsically safe grounding, with the grounding resistance being less than 1 ohm.

What’s the point of using intrinsically safe devices without installing a safety barrier? It’s still a 4-20mA signal, so it shouldn’t affect the display, right? The issue is simply that it’s not safe enough for use in the field, as it could pose risks such as explosions – is that really the case?

If the field instruments are intrinsically safe, safety barriers cannot be used, because using a safety barrier would not enable the operation of those field instruments. And because the requirements for intrinsically safe and flameproof cables are different.

I. Zener-type safety barrier 1. The Zener-type safety barrier should be installed in a non-hazardous area; the cross-sectional area of the flexible copper wire leading to the site (hazardous area) must be greater than 0.5 mm2. The insulation strength of the connection wires should be greater than 500V. 2. The wiring of the intrinsically safe side (marked blue) and the non-intrinsically safe side circuits of the Zener safety barrier must not be connected incorrectly or confused. Blue is recommended as the intrinsically safe marking for intrinsically safe wires. In the trunking, intrinsically safe wires and non-intrinsically safe wires should be laid separately, each using its own protective sleeve. On the intrinsically safe side of a Zener-type safety barrier, it is not allowed to have any other power sources, including those from other intrinsically safe circuits. 3. When a Zener-type safety barrier and primary instruments are used to form an intrinsically safe explosion-proof system, it must be inspected and approved by a **designated explosion-proof testing institution. The WP8000-EX series of Zener safety barriers have Co and Lo distribution parameters specified by the **Explosion Protection Inspection Center (CQST)**; these values represent the maximum allowable levels for IIC grade (hydrogen level) applications. For IIB grade environments, these parameters can be multiplied by 3, while for IIA grade environments they can be multiplied by 8. When using cables of different specifications for transmission lines, their inherent cable parameters must be given close attention, and they must not exceed the specified values. 4. When performing separate power-on testing on the Zener safety barrier, it is necessary to pay attention to the model of the Zener safety barrier, the polarity of the power supply, the voltage, as well as the labels on the wiring terminals of the barrier’s housing. 5. It is strictly prohibited to use a megohmmeter to test the insulation between the terminals of a Zener safety barrier. When checking the insulation of the system circuits, all Zener barrier connections must be disconnected first; otherwise, it may cause damage to the internal components. 6. All field instruments connected to Zener-type safety barriers must be instruments that have undergone explosion-proof testing by the relevant explosion-proof authority and obtained an explosion-proof certification. 7. If the internal module of a Zener-type safety barrier needs repair or replacement, in principle, the manufacturer shall be responsible for it. When performing repairs by the user, relevant precautions should be followed; for specific methods, please refer to the repair section. The repair of intrinsically safe instruments is limited to the areas specified, and any other type of repair should be carried out in consultation with the manufacturer. It can be put back into operation only after maintenance; it is not allowed to replace components or structures that affect explosion-proof performance arbitrarily. 8. The installation, use, and maintenance of Zina-type safety barriers shall be carried out in strict accordance with the relevant provisions of GB 3836.15-2000 \"Electrical equipment for explosive gas environments – Part 15: Electrical installation in hazardous locations (except coal mines)\". 9. The safety barrier shall have a reliable grounding, with a grounding resistance not exceeding 4Ω and a wire resistance not exceeding 1Ω. II. Isolated detection terminal and operation terminal safety barriers 1. Isolated safety barriers should be installed in non-hazardous areas. 2. The cross-sectional area of the soft copper wire leading from the isolated safety barrier to the site (hazardous area) must be greater than 0.5 mm2. 3. The insulation strength of the connection wires is greater than 500V. 4. The wiring of the isolated safety barrier’s intrinsically safe terminal (marked in blue) and the non-intrinsically safe terminal circuits must not be connected incorrectly or confused. Blue is recommended as the intrinsically safe marking for intrinsically safe wires. In the trunking, intrinsically safe wires and non-intrinsically safe wires should be laid separately, each using its own protective sleeve. On the intrinsically safe side of an isolated safety barrier, it is not allowed to have any other power sources, including those from other intrinsically safe circuits. 5. When an isolated safety barrier and primary instruments are used to form an intrinsically safe explosion-proof system, it must be inspected and approved by a **designated explosion-proof testing institution. The WP8000-EX series of isolated safety barriers have Co and Lo distribution parameters specified by the **Explosion-Proof Electrical Equipment Inspection Center. These parameters are based on the maximum allowable values for Class II C (hydrogen level); for Class II B environments, these values can be multiplied by 3, while for Class II A environments, they can be multiplied by 8. When using cables of different specifications for transmission lines, their inherent cable parameters must be given close attention, and they must not exceed the specified values. 6. When performing separate power-on testing on the isolated safety barrier, it is necessary to pay attention to the model of the isolated safety barrier, the polarity of the power supply, the voltage level, and the labels on the wiring terminals of the barrier’s enclosure. 7. It is strictly prohibited to use a megohmmeter to test the insulation between the terminals of the isolation barrier. When checking the insulation of the system wiring, all isolation barrier connections must be disconnected first; otherwise, it may cause damage to the internal components. 8. All field instruments connected to the isolation safety barrier must be those that have undergone explosion-proof testing by the relevant explosion-proof authority and obtained an explosion-proof certification. 9. If the internal modules of an isolated safety barrier need to be repaired or replaced due to damage, in principle, the manufacturer shall bear the responsibility. When performing repairs by the user, relevant precautions should be followed; for specific methods, please refer to the repair section. The repair of intrinsically safe instruments is limited to the areas specified, and any other type of repair should be carried out in consultation with the manufacturer. It can be put back into operation only after maintenance. 10. The installation, use, and maintenance of isolated safety barriers shall be carried out in strict accordance with the relevant provisions of GB 3836.15-2000 \"Electrical equipment for explosive gas environments – Part 15: Electrical installation in hazardous locations (except coal mines)\". 11. For products that have obtained an explosion-proof certification, it is not allowed to arbitrarily replace components or structures that affect their explosion-proof performance. III. Common Issues with Safety Gates 1. What are the common explosion-proof types? Which situations are they suitable for respectively? According to IEC standards, explosive gas hazardous areas can be divided into Zone 0, Zone 1, and Zone 2. Zone 0 refers to areas where an explosive gas mixture is present continuously or for an extended period under normal conditions; Zone 1 refers to areas where an explosive gas mixture may occur under normal conditions ； Zone 2 refers to areas where, under normal conditions, explosive gases are unlikely to occur or, if they do appear, only for a short period of time. Therefore, Zone 0 is the most dangerous area, and the explosion-proof requirements for Zone 0 are the strictest; intrinsically safe type IA is mandatory. The requirements for Zone 1 are relatively less stringent; it can be intrinsically safe (either IA or IB), or it can be of the flameproof type, or of the increased safety type. There are also several less common types that can be used for explosion protection in Zone 1, namely: positive pressure type, oil-filled type, sand-filled type, and hermetically sealed type. In addition, it can also be a specially designed explosion-proof version. For Zone 2, a non-sparking type with the weakest explosion protection requirements can be used; of course, any explosion-proof type that meets the explosion protection requirements for Zones 0 and 1 can also be employed. One thing to keep in mind is that, regardless of the type of equipment, it must undergo certification by an explosion-proof testing agency and obtain an explosion-proof certificate before it can be used. 2. When do I need to use an intrinsically safe system? There are various explosion-proof types for gases prone to explosion, which can be classified as Zone 0, Zone 1, and Zone 2. The explosion protection requirements for Zone 0 are the strictest; only intrinsically safe types are permitted. In Zones 1 and 2, it would be ideal to be able to use intrinsically safe types. Furthermore, the intrinsically safe design is simple to implement, and no excessive protective measures are required for field equipment (an explosion-proof certificate is also not needed). For \"simple devices\" such as thermal resistors and switches, the advantages of the intrinsically safe design are particularly evident. Therefore, intrinsically safe systems are currently accepted and favored by people. As a key component of intrinsically safe systems, safety barriers are attracting increasing attention. As joint forensics in domestic settings is gradually being replaced by the internationally popular parameter-based forensics, it has become possible for engineers to directly select safety barriers. This also indirectly accelerated the adoption of intrinsically safe systems in China. 3. How does a safety barrier achieve explosion protection? In China, intrinsically safe systems are receiving 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-proof properties of safety barriers. Whether it is a Zener safety barrier or an isolated safety barrier, both achieve the requirements specified for explosion protection by controlling energy. A Zener safety barrier – as the 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 gate 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. 4. Should I use an 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, they 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. 5. How should I determine the parameters of the safety barrier? The selection of a safety barrier is crucial in its use; choosing the right safety barrier is fundamental to ensuring the explosion protection of the system. When selecting a safety barrier, two factors must be taken into account: First, to ensure the proper operation of the system, it is necessary to determine the parameters of the safety barrier based on the system’s specifications. For Zener safety barriers, key parameters include the operating voltage, maximum operating voltage, and terminal resistance; for isolation safety barriers, the accuracy level that can be achieved is the important factor to consider. Of course, whether it is a Zener safety barrier or an isolation safety barrier, the working environment also needs to be taken into consideration, such as the operating temperature and humidity, as well as whether the installation method is convenient for on-site setup. Secondly, it is necessary to determine the explosion protection level required based on the area that needs to be protected against explosions – whether it is Zone 0, Zone 1, or Zone 2 – and then decide whether an ia-rated or ib-rated safety barrier should be used. 6. 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 an intrinsically safe system. 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 crucial factor. Especially after parameter authentication replaces system authentication, engineers need to pay particular attention to this issue. Second, attention must 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 making replacements. 7. Why is fieldbus difficult to adopt in the petrochemical industry? Fieldbus is highly favored by engineers for its advantages such as simple structure, easy scalability, and cost savings. However, it is not easy to implement this in the petrochemical industry. The main reasons for this are as follows: First, 70%-80% of the areas in the petrochemical industry are hazardous zones, and explosion prevention is the primary concern in petrochemical automation. Safety barriers are effective components for controlling energy at the field level, but they also limit the capacity of bus devices. This prevents the main advantages of fieldbus from being realized. Secondly, due to the special conditions at the site, the inability to perform maintenance on equipment while it is still powered also hinders the development of fieldbuses. Third, the lack of widespread use of smart meters with explosion-proof functions is also one of the reasons why fieldbus technology has not developed well in the petrochemical industry. Fourth, the increasing maturity of domestic DCS systems also puts fieldbus systems, which are still in the developmental stage, at a disadvantage in the petrochemical industry. If the automation systems in this industry fail entirely, it would cause huge losses to companies; this further underscores the need for the petrochemical industry to use DCS systems that do not cause failures to spread to other equipment and are already well-developed. Of course, the advantages of on-site systems have already been recognized, and their application in the petrochemical industry is only a matter of time; this will depend on the efforts of FCS manufacturers and other companies in related industries.

If the field instruments are intrinsically safe, there is no need to install a safety barrier on the DCS side； If the field instruments are intrinsically safe, it is also necessary to check whether the DCS I/O cards are intrinsically safe as well. If so, then the entire circuit is already intrinsically safe, and a safety barrier is not required. If not, it is necessary to install a safety barrier.

Instrument explosion-proof types do not require a safety barrier.

I also want to know whether an intrinsically safe transmitter on site can actually be used with a safety barrier.

A intrinsically safe circuit requires an intrinsically safe instrument, an intrinsically safe cable, and a safety barrier – none of these can be missing. Adding a safety barrier to a non-intrinsic safety instrument does not enable the creation of an intrinsic safety circuit; it is meaningless. Moreover, if the field meter is powered by a circuit, it may also result in insufficient power supply for the field meter. :)

This is related to how the hazardous areas are defined in your installation; if it is Zone 0 or 1, intrinsically safe instruments must be used, and safety barriers must be installed on the DCS side.

It seems like it needs to be added; otherwise, it could cause problems if something goes wrong