Siemens' fail-safe module is a safety device widely used in industrial control systems, and its main purpose is to ensure the safety and reliability of equipment operation.
The following will introduce SFDOOR among the Siemens security functions from four aspects:
Problem Description
In the industrial field, the safety door is one of the key devices to prevent accidental injury and improve production efficiency. Safety doors can ensure the health and safety of employees and other related personnel, and reduce the risk of accidents during machine operation.
To ensure the safety of workers, a door is provided in the closed part of the machine, and a safety interlock switch is installed to indicate the status of the door to ensure the safety of the machine or process. Limit switches are the most common setting for safety door interlocks, usually with two opposing limit switches mounted on the door. When opening or closing the door, only one limit switch will close, as shown in the picture below.
Figure 1 shows that when the door is open, switch 1 will be closed and switch 2 will be open. When the door is closed, the opposite is true, switch 1 is on and switch 2 is off. This setup provides an extra level of security and monitoring, since both switches cannot be off or on at the same time. If this happens, it means that one of the switches has failed and will trigger the safety function.
Also, switches 1 and 2 may be dual-channel switches, each with two independent channels, due to redundancy principles. In this example, we assume that each switch has two channels. Therefore, the safety PLC will monitor the system as follows:
The safety PLC will mutually monitor each switch's dual channels and keep them in the same position at all times, otherwise something could go wrong inside the switch. The safety PLC will mutually monitor the two switches 1 and 2, keeping them facing each other at all times, otherwise one of the switches may fail. In any case, the safety PLC will trigger the safety function and confirm all safety conditions until restored.
