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# Linearity Calibration of High Resolution CRT and Photo Interpreter Tables

IP.com Disclosure Number: IPCOM000092255D
Original Publication Date: 1968-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 39K

IBM

## Related People

Clodfelter, JA: AUTHOR

## Abstract

This method checks the linearity of a cathode ray tube CRT. A high precision circle, slide, or template 10 is superimposed over the face of CRT. Exact positioning of template 10 is not critical. A measure of the linearity of any X-Y deflection system, where X-Y means independent motion along two orthogonal axes, can be obtained. The method relies on the fact that any connected right triangle inscribed in a circle has a hypotenuse defining the diameter of the circle.

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Linearity Calibration of High Resolution CRT and Photo Interpreter Tables

This method checks the linearity of a cathode ray tube CRT. A high precision circle, slide, or template 10 is superimposed over the face of CRT. Exact positioning of template 10 is not critical. A measure of the linearity of any X-Y deflection system, where X-Y means independent motion along two orthogonal axes, can be obtained. The method relies on the fact that any connected right triangle inscribed in a circle has a hypotenuse defining the diameter of the circle.

Template 10 is placed such that it intersects the CRT trace at x(o)y(o), x(f)y(o), and x(f)y(f). The measured lengths x(f)-x(o) and y(f)-y(o) are used to determine the hypotenuse of the right triangle.

A comparison of the length of the hypotenuse, thus obtained, with the known diameter of the circle provides a measure of the linearity of the X-Y deflection system.

In order to measure linearity automatically, the flying spot scanner FSS proceeds under computer control. Starting from the left, the FSS proceeds along an X line until a photomultiplier tube PMT detects a circle crossing at x(o)y(o). When the FSS reaches the circle at x(f)y(o), The computer then computes the distance d between x(f)y(f) and x(o)y(o) by the equation d = square root of (x(f)- x(o))/2/ + y(f)-y(o))/2/. Comparison of d, thus obtained, with the known diameter of the circular template 10, provides a measure of the linearity of the X-Y deflection system. The...