I. The main characteristics of PLC
(1) High reliability
1. All I/O interface circuits are photoelectric isolation, so that the external circuit of the industrial site is connected with
The internal circuits of the PLC are electrically isolated.
2. R-C filter is used at each input end, and the filtering time constant is generally 10~20ms.
3. Each module adopts shielding measures to prevent radiation interference.
4. Use switching power supply with excellent performance.
5. Strict screening of the devices used.
6. Good self-diagnosis function, once the power supply or other software, hardware abnormal situation, CPU
Take effective measures immediately to prevent the failure from spreading.
7. Large PLC can also use a redundant system composed of two cpus or a three-CPU voting system
System, further improve the reliability.
(2) Abundant I/O interface modules
PLC for different industrial field signals, such as:
• AC or DC;
• Switching quantity or analog quantity;
• Voltage or current;
• Pulse or potential;
• Strong or weak electricity, etc.