Active cables refer to the cable with electronic part in the cable. Control and ADC in resistivity system controls the electronic parts in the cable, which controls the current injection. Passive cables refer to the cable with no electronic part in the cable. One of the advantage of passive cables is its ability to borehole and marine surveys, operator can put passive cables in water. Putting active cables in water will damage the electronic parts.
FlashRES resistivity meter uses passive cable, thus it can do borehole, surface-hole and crosshole survey.