SER 1 contains the OSH 256R passive optical scanning head which is designed for reading the status indication LEDs of protection relays. For connecting its binary output signal to one of the binary inputs of a CMC test set, the interface box IFB 256 is used.

The lightweight scanning head can be attached to smooth surfaces by means of its suction cup or by a re-usable adhesive rubber compound in case of a non-planar surface. The adhesive rubber compound additionally screens the sensor from ambient light.