A clearance sensing system is disclosed. The system includes a probe separated from a test object by a variable distance d. The system also includes an alternating current (AC) source for supplying a current through the probe, wherein the AC source and the probe are configured to generate a controlled plasma channel between a tip of the probe and the test object. The system further includes a processing unit configured to determine the variable distance d based on a voltage difference between the tip of the probe and the test object.