Rockwell Automation 2755 High Performance VLD Scanner - Manual (Page 53)

Glossary G–5
Pitch
1) Rotation of a code pattern about the Y axis. 2) The normal
distance between the centerline or adjacent characters.
Pre-printed Symbol
A symbol which is printed in advance of application either on a label
or on the article to be identified.
Print Contrast Signal (PCS)
A measurement of contrast (brightness difference) between the bars
and spaces of a symbol. A minimum PCS value is needed for a
symbol to be scannable. PCS - (R
L
- R
D
)/R
L,
where R
L
is the
reflectance factor of the light background and R
D
is the reflectance
factor of the dark bars.
Print Quality
The complete analysis of a printed symbol with regard to reflectance
properties as well as bar and space resolution with regard to symbol
specification. The inter-relationship of printed material and
imprinted material that affects the optimum performance of the
scanner.
Quiet Zone, Quiet Area
An area preceding and following a bar code symbol that contains no
printing. The length of the quiet zone must be at least 10 times the
narrow bar width.
Read
A successful read of a bar code symbol.
Reflectance
The amount of light returned from an illuminated surface.
Reflectance, Absolute
The ratio of the total reflectance by a document to the total light
incident on the document.
Reflectance, Diffuse
Reflected light whose angle of reflection varies from the angle of
incidence of the illuminating light, as in reflection from
a mirror.
Reflectance, Specular
Reflected light whose angle of reflection is equal, or nearly equal, to
the angle of incidence of the illuminating light, as in reflection from
a mirror. Specular reflectance is the reason why the scanner should
be aligned 10 to 20
_ off center.