Safety barrier, also known as safety limiter, is widely used in intrinsically safe level meters and is a crucial component of intrinsically safe explosion protection systems. Safety barrier refers to the component that is connected between the intrinsically safe circuit and the non-intrinsically safe circuit. It is a safety performance device that limits the voltage and current supplied to the intrinsically safe circuit to a certain safety range. In brief, the main function of the barrier is to prevent dangerous energy in the security zone from entering the danger zone, so that the voltage and current sent to the danger zone are limited.
The main safety barrier is divided into two major types of Zener safety barrier and Isolated Safety Barrier.
Zener diodes, also known as zener diodes and zener diodes, are the core components of the Zener barrier. In a Zener type safety barrier circuit, in order to limit the energy transmission in a hazardous area, a quick fuse, a current limiting resistor, or a voltage limiting diode is often used to limit the input power.
The working principle of the Zener safety barrier is simple and inexpensive, but its reliability is not high, which limits its application scope to a large extent. The specific installation requirements are:
1. It must be installed in a complete grounding system. For safety protection, the grounding resistance of the Zener Barrier should be less than 1Ω. However, such requirements are difficult to achieve in practical engineering applications.
2. The circuit principle of the Zener-type safety barrier needs to absorb the energy of the input circuit and easily cause the output to be unstable.
3, Zener safety barrier has a great impact on the power supply, at the same time, it is also very easy to damage due to power supply fluctuations.
4. The instruments in the hazardous area must be of isolated type. Otherwise, the signal transmission cannot be guaranteed by connecting the ground terminal of the Zener type safety barrier to the ground. Because signal grounding directly reduces the anti-interference ability of the signal, it greatly affects the stability of the system itself.
In contrast, isolated barriers not only have limited energy capabilities, but also have isolation capabilities. They are mainly composed of loop energy limiting units, signal and power isolation units, and signal processing units.
Isolated safety barriers adopt a circuit structure that electrically isolates the input, output, and power supply from each other, fully complying with the intrinsically safe limits of energy requirements. Although the price is slightly higher, its more prominent advantages can bring more benefits to users, specifically:
1. Three-way isolation is adopted, no system grounding circuit is required, which brings great convenience to design and site construction.
2. The signal line does not need common ground, so that the stability of the detection and control loop signal and the anti-interference ability are greatly enhanced, and the reliability of the entire system is improved.
3, with good input signal processing capabilities, able to accept and deal with thermocouples, thermal resistance, frequency and other signals.
4. There are not many requirements for instruments in hazardous areas. There is no need for isolated instrumentation.
5. Two sets of isolated signals can be output to provide to two devices using the same signal source, and to ensure that the signals of the two devices do not interfere with each other, and at the same time, the electrical safety insulation performance of the connected devices can be improved.
Today, isolated safety barriers are widely used in level receivers such as RF admittance level switches, anti-rotation level switches, and float level gauges. In general, the characteristics and performance of Zener barriers and isolated barriers are very different. Isolated barriers have significant advantages and are widely used. Their price is higher than that of Zener barriers. From the design, construction, installation, commissioning and maintenance costs, its comprehensive cost and convenience are far more advantageous than those of the Zener Barrier. Today, in demanding conditions, isolated safety barriers are used almost exclusively as intrinsically safe explosion-proof meters. In other words, zener safety barriers have now been gradually replaced by isolated barriers.
The above is related to the introduction of "safety barrier type analysis". For more information on level switches, level switches, and magnetic level gauges, please pay attention to WeChat public number: Jiweimeter. (The article is taken from:, please indicate the source.)
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