The S21 sensor is a digital probe for nonreactive transmissions of binary signals out of the device under test during a burst testing. The sensor is positioned directly onto the PC board of the device under test and is powered by the device under test. In the sensor the digital signal is transformed into an optical signal and is transmitted via a fibre optical cable to the receiver/ oscilloscope.
 
Signal transmissions via a fibre optic cable do not change the testing environment of the device under test while the signals received allow the device under test`s concrete functions to be controlled, meaning disturbed signals can be immediatly detected.