1. Definition
1. Signal isolator (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.
2. Signal isolation safety barrier (Safety Barrier): 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 certain safety range. Safety barrier is a general term, divided into Zener safety barrier and isolated safety barrier. Isolated safety barrier is referred to as isolation barrier.
2. Working principle
1. The working principle of signal isolator:
First, the signal of the transmitter or instrument is modulated and converted by semiconductor components, and then isolated and converted by light-sensitive or magnetic-sensitive devices, and then demodulated and converted back to the original signal before isolation, and the power supply of the isolated signal is isolated. . Ensure that the transformed signal, power, and ground are absolutely independent.
2. The working principle of Zener safety barrier:
The main function of the safety barrier is to restrict 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 safe limit voltage value, the Zener tube is turned on, so that the voltage across the Zener tube is always kept below the safe limit value. The resistor R is used to limit the current. When the voltage is limited, the resistance value is appropriately selected to limit the loop current below the safe current limit value.
The function of the fuse F is to prevent the zener tube from being blown out by the large current flowing for a long time and causing the loop voltage limiting failure. When a voltage exceeding the safety limit voltage is applied to the loop, the Zener tube is turned on. If there is no fuse, the current flowing through the Zener tube will rise indefinitely, and the Zener tube will eventually be blown, causing the bribe to lose the pressure limit. In order to ensure the safety of bribery limiting voltage, the speed of the fuse is ten times faster than the speed at which the Zener tube may be blown.
3. The working principle of isolated signal isolation safety barrier:
Compared with the Zener safety barrier, the isolated safety barrier not only has the function of voltage and current limitation, but also has the function of galvanic isolation. The isolation barrier is usually composed of three parts: loop energy limiting unit, current isolation unit and signal processing unit. The loop energy limiting unit is the core part of the safety barrier. In addition, there is a bribe power supply circuit for driving field instruments and a detection circuit for instrument signal acquisition. The signal processing unit performs signal processing according to the functional requirements of the safety barrier.
3. Functions and advantages
1. Signal isolator function
Protect the lower-level control loop.
Reduce the influence of environmental noise on the test circuit.
Suppress the interference of public grounding, frequency converter, solenoid valve and unknown pulse to the equipment; at the same time, it has the function of limiting the pressure and the flow rate for the lower equipment. It is the transmitter, instrument, frequency converter, solenoid valve, PLC/DCS input and output and communication interface The faithful protection.
2. Isolated safety barrier
It adopts a circuit structure that electrically isolates the input, output and power supply from each other, and at the same time meets the requirements of intrinsically safe limited energy. Compared with Zener-type safety barriers, although the price is more expensive, its outstanding performance advantages have brought greater benefits to user applications:
Due to the three-way isolation method, there is no need for system grounding, 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.
Isolated safety barriers have stronger input signal processing capabilities, and can receive and process thermocouple, thermal resistance, frequency and other signals, which this Zener safety barrier cannot do.
The isolated safety barrier can output two mutually isolated signals to provide to 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 of the connected devices.
In 2008,a new industrial park of Liandajin was built in Daya Bay National Economic Development Zone,huizhou with CNY120 million.The Park covers an area of 20000 square meters including 12000 square meters of manufacturing plant,The employees has been up to 1000 and the output has been 60000 square meters per month.
PCB,PCB Manufacturer,PCB Fabricator,Circuit Board,Printed Circuit Board
Huizhou Liandajin Electronic Co., Ltd , https://www.ldjpcb.com