What is the purpose of an isolation safety barrier? What are its characteristics?
发布时间：
2022-05-09
What is the purpose of an isolation safety barrier, and what are its characteristics? Circuit energy-limiting devices that restrict electrical energy in a circuit to achieve intrinsic safety and explosion-proof functionality are commonly referred to as isolation safety barriers. So, what is the purpose of an isolation safety barrier, and what are its characteristics?
What is the purpose of an isolation safety barrier? What are its characteristics?
Circuit energy-limiting devices that restrict electrical energy in a circuit to achieve intrinsically safe explosion-proof functionality are commonly referred to as isolation safety barriers. So, what is the purpose of an isolation safety barrier, and what are its key characteristics?
I. The Function of Isolation Safety Barriers
Isolation safety barriers typically consist of three main components: a loop energy-limiting unit, a current-isolation unit, and a signal-processing unit. The core circuit of the loop energy-limiting unit is the fundamental energy-limiting circuit that defines the basic functionality of the isolation safety barrier. In addition, there are auxiliary circuits for powering field instruments and for signal acquisition and detection. The current-isolation unit comprises transformer-based isolation elements, as well as mod-to-frequency and frequency-to-mod conversion circuits. The signal-processing unit performs signal conditioning and processing in accordance with the specific functional requirements of each type of isolation barrier. Therefore, in general, the primary functions of an isolation safety barrier are loop energy limitation, current isolation, and signal processing.
II. Characteristics of Isolation Safety Barriers
There are two types of isolation safety barriers: Zener-type isolation safety barriers and barrier-type isolation safety barriers. Compared with Zener barriers, barrier-type isolation safety barriers are more expensive but offer greater advantages and distinctive features.
1. Isolating barriers can effectively isolate field circuits in hazardous areas from the control system in the safe area of the control room. This isolation offers three key benefits: first, isolating barriers do not require intrinsically safe grounding, thereby simplifying the engineering implementation of intrinsically safe explosion-proof applications; second, the immunity of both the sensing and control loops to electromagnetic interference is significantly enhanced; and third, field instruments are permitted to be grounded without interfering with the grounding of the control system.
2. The use of isolation barriers can shorten commissioning preparation time and reduce downtime. This is because isolation barriers offer significantly stronger self-protection than Zener barriers, making accidental damage less likely. In addition, isolation barriers permit live maintenance of field instruments, further minimizing shutdowns.
3. The isolation barrier features robust signal-processing capabilities, offering greater flexibility for field instrumentation and control-system applications and thereby enhancing the efficiency and rationality of the overall system configuration.
4. When both DCS and ESD systems are deployed, selecting an isolation barrier with one input and two outputs can effectively isolate the two systems, thereby preventing a failure in one system from affecting the normal operation of the other.
When selecting an appropriate isolation safety barrier, pay attention to the following aspects during use.
First, attention must be paid to the capacitive and inductive reactances of cables and field devices. Explosion protection pertains to the entire system. In addition to the required explosion-proof rating for isolation barriers, the energy storage characteristics of cables and field devices are also a critical issue. Particularly after parameter certification has replaced system certification, engineers must pay close attention to this aspect.
Second, ensure proper grounding. The Zener isolation safety barrier must be grounded, with a grounding resistance of less than 1 ohm.
Third, cables and non-cables shall be routed separately in different cable trays, and clear labeling shall be provided.
Fourth, ensure the power is turned off when replacing.
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