System Examination: Drive Electronics

These days, modern frequency converters or servo amplifiers have an integrated safe shutdown path, through which the STO safety function can be performed. This shutdown path is generally accessible externally via a terminal pair and must be connected to 24 V DC. If the safety function is not in use, 24 V DC will be available permanently at the terminals. If the shutdown path is used as an STO or safe reset lock, the terminals must be connected to a safe output on a programmable safety system or safety relay. In this case it is important to ensure that the test pulse on the safe output does not initiate the safety function. A countermeasure is to use an input
filter with an appropriate time delay. Depending on the version, a feedback path is available for fault detection, to achieve greater safety integrity.

The benefits of a drive-integrated shutdown lie mainly in the:

• Reduced wiring requirement
• Rapid restart, as the intermediate circuit remains charged
• Short reaction time (measured from the falling edge at the input to the shutdown of the optocoupler, the reaction time is in the millisecond range)