The instrument has a built-in GM counter and additionally provides a probe socket to connect external probes. If a probe is connected, the internal counting tube is automatically turned off; the detector of the probe is now measuring. The type of the probe is automatically recognized (e.g. display "ext 17" when a 6150AD-17 probe is connected). Display range and units are chosen automatically according to the type of the probe. Also, there is no fixed assignment between probe and instrument. That means you may connect any probe with any 6150AD, where probe indication will not depend on the 6150AD in use. One pin of the probe socket serves as serial interface and can be used to transmit and evaluate the display (dose rate) of the instrument on a PC. Cables to connect external probes may be up to 100 m long (depending on probe type). Standard lengths available from stock are 1.25 m, 3 m, 10 m, 20 m, 75 m, and 100 m.