Signal isolation safety gate

I. Definition

1. isolator: Generally refers to the signal isolator in the weak current system, which protects the lower signal system from the influence and interference of the higher system.

2. Signal isolation safetybarrier: It is connected between basic safety circuit and non-basic safety circuit. A device that limits the voltage or current that supplies a basic safety circuit to a certain safety range. Safety gate is a general term, divided into Zener safety gate and isolation safety gate, isolation safety gate referred to as isolation gate.

Ii. Working principle

1. The working principle of the signal isolator: first, the signal of the transmitter or instrument is modulated through the semiconductor device, then isolated and converted through the optical or magnetic sensing device, and then demodulated and converted back to the original signal before isolation, while isolating the power supply of the signal after isolation. Ensure the transformed signal. Power supply. Absolute independence between the ground.

2. The working principle of Zener-type safety grid

The main function of the safety grid is to limit the dangerous energy from the safe place into the dangerous place and limit the voltage and current sent to the dangerous place.

Zener tube Z is used to limit voltage. When the circuit voltage is close to the safe limit value, the Zener tube is switched on so that the voltage at both ends of the Zener tube is always kept below the safe limit value.

Resistance R is used to limit the current. When the voltage is limited, the appropriate resistance value can be selected to limit the circuit current below the safe limit.

The function of fuse F is to prevent the failure of circuit voltage limit due to the burning of large current flowing for a long time. When a voltage above the safe voltage limit is added to the circuit, the Zener tube is opened. If there is no fuse, the current through the Zener tube will rise indefinitely, eventually burning the Zener tube, causing the circuit to lose voltage limit. To ensure the safety of the circuit voltage limit, the fuse was blown ten times faster than the Zener tube could be blown.

The basic energy limiting circuit structure of the three-redundant Zener tube safety gate as shown in Figure 1 is adopted to ensure the normal operation of the safety gate. When one fault point and two fault points, the output energy of the safety gate can be limited to the range specified by the safety parameters to meet the requirements of the class ia intrinsically safe circuit.

3. Isolation signal Isolation safety grid working principle

Compared with Zener safety gate, the isolation safety gate not only has the function of voltage limit and current limit, but also has the function of current isolation. The isolation gate usually consists of a circuit energy limiting unit. The current isolation unit and signal processing unit are composed of three parts, and the basic functional circuit is shown in Figure 2. Circuit energy limiting unit is the core part of safety gate. In addition, auxiliary circuit power supply circuit and instrument signal acquisition and detection circuit. The signal processing unit performs signal processing according to the functional requirements of the safety gate