Profilograph

in metalworking, an instrument for measuring surface irregularities and displaying the results in the form of a curve characterizing the waviness and roughness of the surface. The curve is subjected to graphic analysis.

A profilograph uses a sensing stylus that moves perpendicularly to the surface being measured; oscillations from the stylus are optically or electrically converted into signals that are recorded on photosensitive film or paper. The first profilographs appeared in the late 1930’s and were opticomechanical devices for recording a signal on motion-picture or still photographic film. In modern profilographs, the oscillation of the stylus is usually converted into voltage oscillations using induction, capacitance, and piezoelectric converters.

Profilographs consist of three units: (1) a bedplate, with a measurement stand and a drive mechanism, (2) an electronics module, and (3) a recording device. A diamond stylus with a radius of curvature of 2–12 microns is mounted on a sensor. The static pressure of the stylus on the surface being measured varies from 1 to 20 millinewtons(l millinewton = 0.1 gram-force); the pressure under dynamic conditions varies from 0.06 to 1.2 millinewtons for 1 micron of axial displacement of the stylus. The recording of the profile using instruments with electric conversion of the signal is most often done on metal-coated paper. For ease of interpretation, the curve is traced on an enlarged scale. The recording of the measured heights of the irregularities may be amplified by a factor of 400 to 200,000. Horizontal amplification up to a factor of 100,000 is achieved as a result of the rapid motion of the paper relative to the rate of displacement of the stylus.

The error in the vertical amplification for different types of instruments ranges from ±5 to ±10 percent, and in the horizontal amplification the error is no more than ± 10 percent. Profilographs are usually manufactured in units that include a profile meter and are equipped with attachments that permit profiles of parts with various shapes to be measured.