The safety barrier limits the energy entering the site, that is, the voltage and current limit, so that the field line will not generate sparks under any state, so that it will not cause an explosion. This explosion-proof method is called intrinsic safety. Our common safety barriers include zener safety barriers, transistor safety barriers, and transformer isolated safety barriers. These safety barriers have their own advantages and are all helpers in industrial production. The following editors from Suixianji.com will introduce the working principle and function of the safety barrier, as well as the difference from the isolation barrier.
Safety barrier is a general term, divided into zener safety barrier and isolation safety barrier, isolated safety barrier is referred to as isolation barrier.
How the safety barrier works
1. Working principle of signal isolator:
First, the signal of the transmitter or instrument is modulated and transformed by a semiconductor device, and then isolated and converted by a light-sensitive or magnetic-sensitive device, and then demodulated and converted back to the original signal before isolation, and the power supply of the isolated signal is isolated at the same time. . Ensure that the converted signal, power supply and ground are absolutely independent.
2. Working principle of Zener safety barrier:
The main function of the safety barrier is to limit the dangerous ability of the safe place to enter the dangerous place, and to limit the voltage and current sent to the dangerous place.
Zener Z is used to limit the voltage. When the loop voltage is close to the safety limit value, the Zener is turned on, so that the voltage across the Zener is always kept below the safety limit. Resistor R is used to limit the current. When the voltage is limited, proper selection of the resistor value can limit the loop current below the safe current limit value.
The function of the fuse F is to prevent the circuit voltage limiting failure due to the zener tube being blown by a large current flowing for a long time. When the voltage exceeding the safe voltage limit value is applied to the circuit, the Zener tube is turned on. If there is no fuse, the current flowing through the Zener tube will rise infinitely, and eventually the Zener tube will be blown, so that the bribe loses its voltage limit. To make sure the bribe voltage limiter is safe, the fuse blows ten times faster than the Zener can potentially blow.
3. The working principle of the isolated signal isolation safety barrier:
Compared with the zener safety barrier, the isolated safety barrier has the function of galvanic isolation in addition to the functions of voltage and current limiting. The isolation barrier is usually composed of three parts: the loop energy limiting unit, the galvanic isolation unit and the signal processing unit. The loop energy limiting unit is the core part of the safety barrier. In addition, there are auxiliary power supply circuits for driving field instruments and detection circuits for instrument signal acquisition. The signal processing unit performs signal processing according to the functional requirements of the safety barrier.
The role of safety barriers
Safety barrier is an indispensable safety equipment in many industries. It mainly handles or uses some flammable materials, such as crude oil and some crude oil derivatives, alcohol, natural gas, powder, etc. The leakage or improper use of any of these items will result in an explosive environment. For the safety of factories and individuals, it is necessary to ensure that the working environment will not cause explosions. In the process of these protections, the safety barrier plays a very important role. important role,
The safety barrier is located between the control room and the intrinsically safe equipment in the dangerous place. It mainly plays a protective role. Any electrical equipment in the production process may cause explosion, various frictional sparks, static electricity, high temperature, etc. All are inevitable in industrial production, so the safety barrier provides a protective measure for industrial production.
There must be a very reliable grounding system during the installation process, and the field instruments from the hazardous area must be isolated. Otherwise, the signal cannot be transmitted correctly after being connected to the ground, which will affect the stability of the system.
The difference between safety barrier and isolation barrier
1. Signal isolator function
Protect the lower control loop.
Attenuate the influence of ambient noise on the test circuit.
Suppress the interference of public grounding, frequency converter, solenoid valve and unknown pulse to equipment; at the same time, it has the functions of voltage limiting and rated current for lower equipment, including transmitter, instrument, frequency converter, solenoid valve, PLC/DCS input and output and communication interface faithful protection.
2. Isolated safety barrier
Isolation barrier: Isolated safety barrier, that is, adding isolation function on the basis of the safety barrier, which can prevent the interference of ground loop current to the signal, and at the same time protect the system from the influence of dangerous energy from the scene. For example, if a large current enters the field line, it will break the isolation barrier without affecting the IO. Sometimes it can also be understood as an isolator without a safety barrier function, that is, it only has an isolation function to prevent signal interference and protect the system IO, but does not provide an intrinsically safe circuit. For non-explosion-proof applications.
It adopts a circuit structure that electrically isolates the input, output and power supply from each other, and meets the requirements of intrinsic safety to limit energy. Compared with the Zener safety barrier, although the price is more expensive, its outstanding performance advantages bring greater benefits to user applications:
Due to the use of three-way isolation, there is no need for system grounding lines, which brings great convenience to design and on-site construction.
The requirements for instruments in hazardous areas are greatly reduced, and there is no need to use isolated instruments on site.
Since the signal lines do not need to share the ground, the stability and anti-interference ability of the detection and control loop signals are greatly enhanced, thereby improving the reliability of the entire system.
The isolated safety barrier has stronger input signal processing capabilities, and can accept and process signals such as thermocouples, thermal resistances, and frequencies, which this zener safety barrier cannot do.
The isolated safety barrier can output two mutually isolated signals to provide two devices using the same signal source, and ensure that the signals of the two devices do not interfere with each other, and at the same time improve the electrical safety insulation performance between the connected devices.
The above is about the working principle and function of the safety barrier, and the knowledge of the difference between the safety barrier and the isolation barrier. The signal isolator generally refers to the signal isolator in the weak current system, which protects the lower-level signal system from the influence and interference of the upper-level system. The signal isolation barrier is connected between the intrinsically safe circuit and the non-intrinsically safe circuit. A device that limits the voltage or current supplied to an intrinsically safe circuit within a safe range.
Post time: Nov-26-2022