On this day in 1961 Richard S. Hunter and Clyde A. Lofland were granted the patent for COLOR DIFFERENCE MEASURING INSTRUMENT. U.S. Patent No. 3,003,388.
It is a primary object of the invention to provide a precision photoelectric tristimulus instrument which will give direct values of color on uniform, visually meaningful scales having approximately the spacing of the Munsell color system with precision equal to, or better than the eye trained to detect commercial color differences.
Another object is to provide a compact, rugged, efficient instrument which is simple and not complicated in operation and can be used by unskilled operators with a minimum of training or instruction, yet will give ac curate and reproducible results with great speed.
Another object is to provide a color difference instrument which is easy to read and convenient to operate, incorporating a rugged, yet accurate meter which is unaffected by mechanical vibration such as is often found in industrial surroundings where such instruments are used.
A further object is to provide a color instrument having a relatively few control knobs or wheels, closely spaced for easy reach, and so arranged that the direction of knob or wheel rotation always corresponds to the direction required to bring the balance-indicating device back to zero. setting, which greatly facilitates both speed and ease of operation.
It is also an object of the invention to eliminate mechanical adjustment of photocells required in some previous instruments during the taking of readings, and to provide instead purely electrical circuit adjustments for all operations of the instrument. This permits removal of the sample-observing head from the reach of the operator, as in a monitoring device over a moving web.
Another object is to provide simple digital scales, with zero centered circuit components which eliminate the use of polarity switches when a change in sign of the reading occurs, and which have automatic register means for positively showing the sign of the reading without the possibility of error in reading the sign (or direction) of the value shown on the digital register.
