Scale - [From Latin
scala=ladder,staircase]
- Measurement reference object which possesses graduated
marks or other detectable divisions for reading; the reading may be by mechanical,
electrical, or optical means etc.). Examples: Linear scale, inductive scale, mechanical dial.
- Measurement device which uses a scale (reference object)
to provide a measurement; may read divisions by mechanical,
electrical, visual, or electro-optical means. Examples are rulers,
dial indicators, mercury thermometers, encoders, mass balance.
- Proportional relationship between a graduation mark and a
given measurand value increment. Example:
the thermometer has a scale of 0.1 K per graduation or the dial indicator has a scale of
10 micrometers per division (graduation). In maps, drawings or other graphical
representations such as architecture, the proportion may be related to a given distance,
for example, maps and architectural drawings may have a scale of feet per inch, 1 to 100
(any measure), miles per inch etc.
Application Notes
- Machining Centers often use
scales within encoders for positioning feedback.
- Often used as the reference object within an encoder to provide the linear position or angular orientation
of an object with respect to another (such as measuring the position of a carriage with
respect to the ways). Often made of glass. A readhead is
necessary for the encoder to count scale graduations in forward and reverse directions.
Note: The thermal expansion coefficient of the material used in linear scales introduce an
error in the proportional relationship of the measurement and must be compensated to
obtain the most accurate reading. If there is an angular encoder which reads the rotation
of a ballscrew or leadscrew, which
is in the structural loop between the carriage and ways, then the proportional
relationship (between the angular scale graduation and carriage-way displacement) changes
with temperature in the same manner that the pitch of the ball
screw changes (position=graduations x revolutions per graduation x pitch of the
ballscrew).