New paper machine projects or the renovation of old paper machines must take safe operation as a basic principle in the design of control systems. This article takes the Siemens 6SE70 frequency converter (inverter) and S7-300/40 commonly used in paper machine drives as an example to briefly explain the safety control issues involved. [b]1 Safety Control Part of New Hardware System 1.1 Machine Safety Shutdown Control and Detection Circuit[/b] The safety shutdown control and detection circuit is composed of a safety switch and a safety relay on the frequency converter. Its working principle is shown in Figure 1. When safe operation is required, the safety switch on the control panel is turned to the off position. Relay K1 is de-energized. The IGBT control power supply is de-energized. Even if the frequency converter microprocessor outputs a trigger command, the main power circuit will not work. At the same time, the safety status detection indicator light illuminates, indicating to the operator that the drive device is in a safe shutdown state. The safety switch can be a Siemens 3LB2000 series combination switch, with two positions, two normally open contacts, and two normally closed contacts. Most importantly, its mounting section has three holes; in the off position, the switch can be locked using a lock or rope through two of these holes to prevent unauthorized operation. The safety switch can be configured according to the drive group. For example, in the wire section, the drive roller and the pawl roller form a load distribution control drive group. In practical applications, one safety switch is configured, with its two K1 switches connected in parallel. The normally closed feedback contact of the safety relay is connected in series to the safety status indicator circuit. [b][align=center]For more details, please click: Safety Control in Paper Machine Electrical Drives[/align][/b]