HEIDENHAIN Length Gauges - Manual (Page 12)

12
Measuring accuracy
The accuracy of linear measurement is
mainly determined by
• the quality of the graduation,
• the quality of the scanning process,
• the quality of the signal processing
electronics,
• the eccentricity of the graduation to the
bearing,
• the error from the scale guideway
relative to the scanning unit, and
• the orthogonality of the length gauge to
the bearing surface.
These factors of influence are comprised
of encoder-specific error and application-
dependent issues. All individual factors of
influence must be considered in order to
assess the attainable overall accuracy.
Position error a over the measuring length ML
Position er
ror

Position error within
one signal period
Position 
Position error u within one signal period
Signal period
360 °elec.
Signal lev
el

Position er
ror

Error specific to the measuring
device
The error that is specific to the measuring
device is shown in the Specifications as
the system accuracy.
The extreme values of the total error F
with reference to their mean value lie over
the entire measuring length within the
system accuracy ± a. They are measured
during the final inspection and documented
in the calibration chart.
The system accuracy includes
• the homogeneity and period definition of
the graduation,
• the alignment of the graduation,
• the error of the bearing, and
• the position error within one signal
period.
Position error within one signal period
Position errors within one signal period
already become apparent in very small
motions and in repeated measurements.
They are therefore considered separately.
The position error within one signal period
± u results from the quality of the scanning
and—for encoders with integrated pulse-
shaping or counter electronics—the quality
of the signal-processing electronics.
For encoders with sinusoidal output
signals, however, the errors of the signal
processing electronics are determined by
the subsequent electronics.
The following individual factors influence
the result:
• The size of the signal period
• The homogeneity and period definition
of the graduation
• The quality of scanning filter structures
• The characteristics of the sensors
• The stability and dynamics of further
processing of the analog signals
These deviations are to be considered
when specifying position error within one
signal period.
Position error within one signal period ± u
is specified in percent of the signal period.
For length gauges, the value is typically
better than ± 1% of the signal period. You
will find the specified values in the
Specifications.
Short-range accuracy
The short-range accuracy describes an
error that occurs within a distance of
± 100 µm from a measuring point. It
includes electronic and mechanical
influences of the gauge on the result of
measurement. The values for short-range
accuracy typically lie below the specified
values.