Electrical test probe having rotational control of the probe shaft

Abstract

A test probe assembly includes a barrel having a hollow interior and a plunger which slides axially in the barrel. The plunger has an outer portion extending through an open end of the barrel, terminating in a contact tip outside the barrel for contact with a test point. In one embodiment, the plunger also has a hollow, elongated receptacle extending through the barrel. The receptacle has a geometric-shaped pilot hole, preferably square, spaced from the open end of the barrel. An elongated fixed guide member in the barrel extends through the pilot hole. The guide member extends through the interior of the barrel away from the pilot hole. The guide member has an outer surface of preferably square-shaped configuration engaging the pilot hole. A spring inside the barrel extends along the guide member and is biased against the internal end of the receptacle inside the barrel. Axial travel of the plunger into the barrel is against the bias of the spring. The square-shaped outer surface of the guide member, engaging the square pilot hole, controls rotational motion of the plunger as it travels along the guide member against the bias of the spring. In one embodiment, a helical configuration in the outer surface of the guide member engages the pilot hole so that axial travel of the receptacle causes the plunger to rotate about its axis, in order to provide good frictional contact between the plunger tip and the test point on a unit under test. In another embodiment, the cooperating square-shaped engaging portions of the guide member and the pilot hole provide controlled linear and non-rotational travel of the plunger relative to the barrel.