Knowledge Related to Safety Barriers

Characteristics of the Isolated Safety Barrier

The Isolated Safety Barrier is used to protect circuits in hazardous areas and features functions such as energy limitation, isolation, explosion protection, and surge suppression. It can be directly mounted on a DIN 35 rail, or connected via a rail‑bus power supply module. Alternatively, it can be installed using a baseplate. The Isolated Safety Barrier primarily consists of a loop energy‑limiting unit, a signal and power isolation unit, and a signal processing unit; its basic functional block diagram is shown below.

Definition of the Intrinsically Safe Explosion-Proof Marking

Explosion-proof rating

ia: Under normal operating conditions, as well as in the event of a single‑fault or double‑fault condition, it must not ignite an explosive gas mixture. The intrinsically safe side of this type of safety barrier may be connected to intrinsically safe equipment installed in hazardous locations classified as Zone 0, Zone 1, or Zone 2. Electrical equipment of category “ia” must employ a “triple‑redundant” design for components that are susceptible to interference.

ib: Under normal operating conditions and in the event of a single‑channel failure, it must not ignite an explosive gas mixture. The intrinsically safe side of this type of safety barrier may be connected to intrinsically safe equipment installed in hazardous locations of Zone 1 or Zone 2. Electrical equipment of category “ib” shall incorporate redundant design for components that are susceptible to interference.

ic: Under normal operating conditions, it cannot ignite explosive gas mixtures. The intrinsically safe side of this type of safety barrier may be connected to intrinsically safe equipment in Zone 2 hazardous locations.

Equipment Grade

Ga: Equipment for explosive gas atmospheres, with a “very high” level of protection, which does not constitute an ignition source under normal operation, anticipated faults, or rare faults.

Gb: Equipment for use in explosive gas atmospheres, with a “high” level of protection, and which does not constitute an ignition source under normal operating conditions or under the occurrence of foreseeable faults.

Gc: Equipment for use in explosive gas atmospheres, with a “general” level of protection; under normal operating conditions, it is not a source of ignition. Additional protective measures may also be implemented to ensure that, even when ignition sources are expected to occur frequently (e.g., due to lamp failures), effective ignition will not result.

Da: Equipment for explosive dust atmospheres, with a “very high” level of protection, and which does not constitute an ignition source under normal operating conditions, as well as in the event of expected or rare faults.

Db: Equipment for explosive dust atmospheres, with a “high” level of protection, which does not constitute an ignition source under normal operating conditions or in the event of anticipated faults.

Dc: Equipment for explosive dust atmospheres, with a “general” level of protection; under normal operating conditions, it is not a source of ignition. Additional protective measures may also be implemented to ensure that, even when ignition sources are expected to occur frequently (e.g., due to lamp failures), effective ignition will not take place.

Gas group

Temperature class

According to the relevant provisions of China’s national explosion-proof standard GB/T 3836.1-2021, the relationship between the temperature class of electrical equipment, its maximum allowable surface temperature, and the ignition temperature of the applicable gas is as follows:

Classification of Explosive Hazardous Areas

Areas where explosive gas, flammable or combustible liquid vapors mix with air to form an explosive gas mixture are classified into three zone categories based on their degree of hazard.

Intrinsic Safety Performance Certification Parameters for Safety Barriers

The intrinsic safety performance certification parameters for the safety barrier are provided during the product’s explosion-proof certification; the meanings of these parameters are as follows:

·Maximum voltage (AC rms or DC Um): The highest voltage that may be applied to the non-intrinsically safe connection of the associated apparatus without compromising its intrinsic safety performance.

·Maximum Output Voltage (Uo): Under open-circuit conditions, the maximum output voltage of an intrinsically safe circuit—whether AC peak or DC—that may occur when the voltage applied to the equipment connection device reaches its maximum value (including Um and Ui).

·Maximum Output Current (Io): The maximum current (AC peak or DC) that can be drawn from the intrinsically safe circuit connected to the electrical equipment.

·Maximum output power (Po): the maximum power that can be delivered by an intrinsically safe circuit from an electrical device.

·Maximum External Capacitance (Co): The maximum capacitance of an intrinsically safe circuit that can be connected to an electrical equipment connection device without compromising its intrinsic safety performance.

·Maximum external inductance (Lo): the maximum inductance of an intrinsically safe circuit that can be connected to an electrical equipment connection device without compromising its intrinsic safety performance.

Installation Precautions

·This product complies with GB 3836.1-2021 “Explosive Atmospheres – Part 1: Equipment General Requirements” and GB 3836.4-2021 “Explosive Atmospheres – Part 4: Equipment Protected by Intrinsic Safety ‘i’,” and shall be installed, operated, and maintained in accordance with the relevant standards.

·The certification parameters for this product are distribution parameters provided by the National Center for Quality Supervision and Inspection of Explosion‑Proof Electrical Products (CNEX). The test environment corresponds to the maximum permissible values for a Category II C (hydrogen‑rated) atmosphere. For a Category II B environment, these parameters may be multiplied by 3 to obtain the limit values; for a Category II A environment, they may be multiplied by 8.

·This product must be installed in a safe area, and the surrounding air must not contain any substances that could adversely affect chromium, nickel, or silver plating.

·All instruments connected to the safety barrier must be certified as explosion-proof. When the safety barrier and the primary instrument are combined into an intrinsically safe explosion-proof system, the system must be inspected and approved by a nationally designated explosion-proof testing agency.

·Before all connections have been completely disconnected, it is strictly prohibited to use a megohmmeter to directly measure the insulation resistance between terminals; otherwise, the internal fast‑acting fuse may blow.

·In the safety enclosure, intrinsically safe side wiring must not be mixed with non‑intrinsically safe side circuits; any incorrect wiring could result in hazardous conditions. The terminals on the intrinsically safe side of this product are designated in blue, and wiring for intrinsically safe and non‑intrinsically safe circuits shall be routed separately within cable trays.

·Wire selection and installation requirements: cross-sectional area ≥ 0.5 mm²; insulation strength of connecting wires must exceed 500 V.

Introduction to Functional Safety Certification (SIL)

SIL (Safety Integrity Level) is a third-party assessment, verification, and certification process used to evaluate and confirm the safety integrity level (SIL) or performance level (PL) of safety-related equipment, based on standards such as IEC 61508, IEC 61511, IEC 61513, IEC 61508‑1, IEC 62061, and IEC 61800‑5‑2. It primarily encompasses assessments of document management within the safety equipment development process (FSM), hardware reliability calculations and evaluations, software assessments, environmental testing, and electromagnetic compatibility (EMC) testing.

SIL certification is divided into four levels—SIL1, SIL2, SIL3, and SIL4—and encompasses both product‑level and system‑level requirements. Among these, SIL4 represents the highest level of safety integrity.

Certain terms from the SIL standard as referenced in EN 61508 and EN 61511 clauses.

E/E/PES: Electrical/Electronic/Programmable Electronic Systems—this standard applies to all electrical equipment and systems, enabling the specification of safety functions for both simple electrical devices and all types of programmable logic controllers (PLCs).

ECU: Controlled equipment, referring to devices, machinery, apparatus, and systems used in the production, processing, and transportation of raw materials.

MTBF: Mean Time Between Failures, referring to the average time between expected failures.

PDF: Probability Density Function.

PFD: Required Probability of Failure.

PFDavg: the required probability of dangerous failure.

PFH: The required average failure probability (per hour), describing the probability of a hazardous failure occurring per hour.

SFF: Safety Failure Fraction, the ratio of the sum of safety failures and diagnostic or detection failures to the total system failures.

SIS: Safety Instrumented System; an SIS consists of one or more safety-related functions.

During the functional safety certification process, the product is evaluated from the following aspects:

·Assessment of the functional safety management system: To ensure that the implementation of E/E/PE safety‑related systems meets and maintains the required level of functional safety, the managerial and technical activities of the organization or individual responsible for one or more phases of the system’s lifecycle must comply with the requirements specified in GB/T 20438, which is equivalent to IEC 61508.

·Determination of SIL level: failure rate calculation and FMEA analysis; failure rate analyses must be performed for each component of the system, and the results aggregated to derive the system’s average failure rate.

·Evaluation of Performance and Environmental Adaptability: Functional safety imposes stricter requirements on EMC performance, with inspection and testing procedures that are more rigorous than those typically applied to explosion-proof electrical equipment.