Xerox 6180N Generic MICR Fundamentals Guide - Page 109
Quality measurements: magnetic versus optical
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Quality control Quality measurements: magnetic versus optical If a MICR quality issue arises, it should be visible on the printed document. Even signal strength problems can be seen if prints are compared. Low signal characters are thin and poorly formed; high signal characters are fat and usually surrounded by xerographic background. Occasionally, problems are reported by test equipment, but no problem is visible. This is usually due to improper use of intelligent magnetic test equipment, which evaluates optical specifications using magnetic waveforms. Equipment vendors are aware of the limitations of their products, and therefore recommend visual inspection of suspected characters. Some users, however, misinterpret these findings as specifications failures. It is important to understand the differences between optical and magnetic measurements and why all ANSI standards for MICR character dimensions can be evaluated optically only. Magnetic testing equipment usage MICR signal strength is measured magnetically, along with uniformity and spots, and is specified numerically as 50 to 200 per cent of nominal. Waveform uniformity is not specified numerically, but as an indicator for visual inspection. Spots are categorized as magnetic or non-magnetic, because different size allowances apply. No other specifications are measured magnetically. Any MICR failures other than signal strength must be confirmed optically. The following parameters are commonly flagged, but are not specified magnetically: • Character dimensions (±0.003 inch/0.076 mm tolerance) - MICR font dimensions are defined from an "average edge" in the straight portion of a stroke. Waveform-based measurements include the corners, which make magnetic dimensions narrower than average edge separations. Mathematical waveform models of perfect characters show that this can be as large as 0.0013 inch/0.033 mm, which is nearly half the tolerance. - Magnetic edge gradients vary with printing technology. When combined with different MICR tester designs, this variation was shown in a 1993 study to be nearly as large as the dimensions of the character strokes. Generic MICR Fundamentals Guide 6-23