A sense circuit (23) for generating an actuating signal and a method of using the actuating signal to control movement of a wafer chuck (12). The sense circuit (23) has sense input terminals (24, 28) coupled to corresponding probe-card probes (19, 18). A wafer (26) having contact pads (42, 42') is mounted on the wafer chuck (12) and moved towards the probe-card probes (18, 19). When the probe-card probes (18, 19) contact corresponding contact pads (42', 42) on the wafer, the sense circuit (23) generates an actuating signal. The actuating signal, which is generated in accordance with the heights of the contact pads (42', 42), enables control circuit (48) of the prober (11). The control circuit limits the movement of the wafer chuck (12) to prevent damage to the probe card (12) or the wafer (26).