Quality Measurements: Magnetic Versus Optical; Magnetic Testing Equipment Usage - Xerox 6100BD - Phaser Color Laser Printer Fundamentals

Quality measurements: magnetic versus optical

Magnetic testing equipment usage

Generic MICR Fundamentals Guide
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.
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.
Quality control
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