Backscatter instrument for measuring thickness of a continuously moving coated strip of substrate material

A backscatter thickness measuring device for measuring the thickness of a coating on a strip of substrate material moving at a predetermined speed from a feed supply to a take-up location comprising:

• a freely rotatable measurement wheel having a rim and an axle,
• a first guide means for guiding the coated strip of substrate material into frictional engagement with the rim of the measurement wheel;
• a second guide means for guiding the coated strip of substrate material away from frictional engagement with the rim of the measurement wheel to the take-up location;
• means located at the take-up location for drawing the coated strip of substrate material at the predetermined velocity across the first guide means, over a portion of the rim of the measurement wheel and across the second guide means to the take-up location whereby the measurement wheel is rotated about its axle by the frictional engagement of the coated strip of substrate material with the rim of the measurement wheel at a speed such that the tangential speed of a point on the rim equals the predetermined speed of the moving coated strip of substrate material and a point on the rim of the measurement wheel and an adjacent point on the coated strip of substrate material are stationary relative to one another while the measurement wheel is rotating;
• probe means mounted on the rim of the measurement wheel for irradiating the coating on the coated substrate material and detecting the backscattered radiation;
• and
• backscatter measurement means connected to the probe means including means for counting the backscattered radiation and means for determining the thickness of the coating in accordance with the backscatter count.