1, the principle of signal isolator: first of all, the data signal of the intelligent transmitter or instrument panel is converted according to the semiconductor components, and then the protection transformation is carried out according to the gloss or magnetic sensing components, and then the modulation and demodulation are converted back to the original data signal before protection, and the switching power supply of the power supply system after protection of the data signal is protected. Ensure that the converted data signal, switching power supply, and ground center must be separate.

2, the principle of Zener safety grid

The key role of the safety grid is to limit the risk kinetic energy of the safety site into the risk site, and to limit the working voltage and current sent to the risk site.

Zener tube Z is used to limit the operating voltage. When the loop operating voltage is close to the safety limit value, the Zener tube is switched on, so that the working voltage on both sides of the Zener tube is continuously maintained below the safety limit value.

The resistor R is used to limit the current. When the operating voltage is limited, the appropriate resistance value can be selected to limit the loop current below the safety overcurrent protection value.

The function of the safety tube F is to avoid the ineffective circuit voltage limiting caused by the Zener tube being burned out by the large current passing through for a long time. When the operating voltage beyond the safety limit value is applied to the loop, the Zener tube is switched on. If there is no safety tube, the current flowing through the Zener tube will increase endlessly, and then burn the Zener tube, making the loop lose the voltage limit. In order to ensure the voltage limiting safety of the circuit, the fuse fuse rate is ten times faster than the Zener tube is likely to be burned out.

The selection of three-sink Zener tube safety gate base energy limiting power supply circuit structure can ensure that safety gate in all normal operation, one common fault point and two common fault points can limit the output kinetic energy of safety gate within the scope of safety main parameter requirements, and then consider the provisions of ia safety culture power supply circuit.

3, the principle of protected data signal protection security grid

Compared with Zener safety grid, the protective safety grid has the effect of current protection in addition to voltage limiting and overcurrent protection. The guardrail network is generally composed of three parts: circuit energy limiting module, current protection module and signal analysis module. The basic elements of the power supply circuit are shown as shown in Figure 2. The circuit energy limiting module is the key part of the safety grid. In addition, it is assisted by a loop power supply system power circuit for driving the on-site instrument panel and an inspection power circuit for data signal collection on the instrument panel. The signal analysis module carries out the signal analysis according to the function of the safety grid.