Tag Archives: safety plc programming

The difference between safety PLC and general PLC

Safety PLC for alarm function, ordinary PLC can be perfected in the program

Safety PLC (Safety Programmable System) refers to a programmable system that responds correctly and cuts off output in the event of a failure of itself or a peripheral component or actuator.
Unlike ordinary PLCs, safety PLCs not only provide the functions of ordinary PLCs, but also implement safety control functions, complying with the requirements of safety system related components such as EN ISO 13849-1 and IEC 61508.

All components in the safety PLC adopt a redundant diversity structure. When two processors process, cross-detection is performed. The processing result of each processor is stored in the respective memory, and the output is only output when the processing result is completely the same. Any inconsistencies occurred during processing and the system immediately shut down.
1. What role did the safety PLC play in this?
In the system, if the system fails, it may cause personal injury or environmental impact. Therefore, in order to reduce personal injury and environmental impact, there are many methods, such as reducing the probability of failure and reducing risks. Among the methods for reducing the probability of failure is the use of a safety PLC. Reducing risk generally uses physical protection methods.
Therefore, the main purpose of the safety PLC is to implement functional safety functions.
2. Do not understand what security function blocks are used for? Can you give an example?
The safety function block is similar to the general logic operation function block. The main purpose is to design a special function block for the safety control logic. The difference between a safety function block and a normal function block is that a plurality of fault diagnosis pins are added, and the safety function block must be TUV-certified.
3.FB215: When the emergency stop input (E-STOP) is 0, Q is 0, when the emergency stop signal is gone, and the ACK input is 1, then Q is restored to 1. This function block is special as long as we only Connect the emergency stop button to one of the ports, confirm that the button is connected to one of the inputs, and you can achieve the goal. We don’t need logic programming?
Whether programming is required and whether the function of the landlord has been directly output.

Safty plc have written the program, why the main plc still writes the program

You have to create your own FB block or FC block. In the local variable table of the FB, various variables used in the block, INPUT, OUTPUT, TEMP, etc. are created. You also need to build some UDT types, variable references. Doing your own block program requires some practical programming experience. The FB block program is called to create the called instance data block. In the case of FC blocks, the internal local variables are only valid for one cycle, and the variables inside the FB block are different. This is the difference between the two.