Abstract: A grid gates a stream of ions when a D.C. potential is applied between two sets of interdigitated wires included in the grid to produce a D.C. field. The improved grid disclosed herein contains the two sets of interdigitated wires in a single plane so that the D.C. field is precisely normal to the ion current flow direction to prevent a residual ion current flow when the grid provides the gating effect.

Abstract: A rigid structure supporting a motor driven spindle carried in a radially and axially stiff hydrostatic fluid film bearing provides for mounting and rotating a tire at a selected speed including a speed of the tire corresponding to a road speed in excess of 100 miles per hour (approximately 160 kilometers per hour) while the tire is loaded against the cylindrical surface of the freely rotatable load wheel. Force and force variation measurements can be taken by means of measurement frames or load cells including a plurality of strain gauges fixed therein of force and force variation components oriented radially tangentially and axially of the tire which forces are communicated to the spindle and from the spindle entirely through the fluid film of the fluid film bearing to the measuring frames, while the spindle and tire are driven in loaded rolling contact with the load wheel.