Abstract: A needle is pressed into the backside oxide of a semiconductor wafer and a voltage applied to the wafer greater than the breakdown voltage of the oxide in order to make an electrical contact with the bulk material of the wafer. A capacitor plate is provided proximate to a wafer on a chuck and a Kelvin probe is provided proximate to the wafer. A varying voltage is applied between the chuck and the capacitor plate and a voltage is monitored between the Kelvin probe and the chuck. The monitored voltage remaining constant indicates electrical contact between the chuck and the wafer.

Abstract: The chair has a support structure with a wide stable base. The chair has a single inverted U-shaped tubular metal main frame. Near the top and inside of the frame is connected a tubular metal back leg unit set of two legs to swing out away from the inverted U-shaped frame. The support structure is also characterized by possessing:a. A pair of horizontal metal cross-bars affixed within the tubular metal main frame, one near the top and the other near the bottom; andb. A pair of metal tubes attached to and between the cross-bars and situated substantially in the same plane as the main frame.

Abstract: A barrier device for installation in a drain tile adjacent the outlet of the tile includes a plurality of spaced apart barrier elements affixed to a sleeve to define a perforate gate. The gate is swingably mounted on a pivot rod which projects transversely through openings in the tile adjacent the outlet of the latter. The barrier elements, which are in the form of rods, are affixed to the sleeve to normally urge the gate to a closed position by action of gravity to thereby prevent entry by small animals into the tile. The gate may swing to the open position when engaged by floating debris to thereby permit passage of the debris through the drain tile outlet.