Auto detection of guard locking device

A safety switching device for driving a plurality of different kinds of guard locking devices, said safety switching device comprising:

• a first terminal and a second terminal for connecting a guard locking device;
• and
• a safety processor adapted to:
• control a plurality of drive signals, each drive signal output at one of the first and the second terminal to drive the guard locking device,
• detect at least one external electrical connection between at least one of the first terminal and the second terminal and a reference potential,
• determine which of the plurality of different kinds of guard locking devices is connected to the at least one of the first terminal and the second terminal, and
• control the drive signals depending on the determined kind of guard locking device, wherein said plurality of different kinds of guard locking devices is selected from a first kind, of guard locking device having a solenoid, a second kind of guard locking device having a single channel logic input, and a third kind of guard locking devices having dual channel safety inputs,
• wherein the safety processor is adapted to determine:
• that the first kind of guard locking device is connected to the first and the second terminal if a connection between the first terminal and the second terminal is detectable,
• that the second kind of guard locking device is connected to the second terminal if a connection between the second terminal and the reference potential is detectable, and
• that the third kind of guard locking device is connected to the first and the second terminal if neither the connection between the first terminal and the second terminal nor the connection between the second terminal and the reference potential is detectable.