Tire defect tester

A biased electrode for use with apparatus for detecting defects in tires, wherein the apparatus includes means for mounting and rotating a tire, a neutral reference electrode engagable with the outer tread portion of the tire, and a controller unit providing a charge to said biased electrode and an electrical potential across said biased electrode and the reference electrode, comprising:

• (a) A pair of elongated members disposed for pivoting about a common axis, said axis dividing each of said members into first and second arm portions;
• (b) means for positioning said members in first positions within a circumference circumscribed by the tire beads and axially intermediate the beads, wherein said members are biased about said common axis to orientations wherein said first arm portions extend in a direction generally toward the neutral reference electrode;
• and
• (c) means for selectively urging said members to second positions substantially in engagement with an underside of the tread portion of the tire immediately opposite the neutral reference electrode;
• (d) wherein, as said members are urged from their first to their second positions, said first arm portions first engage the underside of the tread portion of the tire and, as said common axis moves farther toward the tread portion, said members pivot about said common axis so that said second arm portions swing away from each other in opposite directions axially with respect to an axis about which the tire is made to rotate, and into engagement with the underside of the tread portion of the tire.