What are OSSD contacts?
OSSD is an abbreviation for “Output Switching Signal Device”. This type of contacts (outputs) is used in safety sensors, safety switches, laser scanners, safety light curtains or for safe control outputs in PLCs.
We increasingly see OSSD contacts in machine safety components. Conventional 24V DC outputs are not designed for safety functions, mainly because they cannot be detected by an external 24V line in the event of a short circuit.
Therefore, both OSSD outputs are switched off with a time delay. During the interval on this output, a built-in input is activated and read back.
If there is 24 V at the input after the OSSD output is switched off, the error is detected and the two internal processors safely switch off both outputs.
OSSD outputs are usually semiconductor or transistor outputs, as opposed to relay or contact outputs. There are usually two independent channels, referred to OSSD1 and OSSD2.
This technology makes it easy to monitor short circuits up to the highest safety level (PLe according to EN ISO 13849-1). Many components with OSSD outputs are equipped with status LEDs, allowing for fast fault detection.