HEIDENHAIN Length Gauges - Manual (Page 15)

15
Whereas the system accuracy applies over
the entire measuring range, for some
applications the repeatability is the decisive
factor. It plays an important role in repeated
measurements.
Repeatability is defined in the standards
DIN 32876 and DKD-R 4-3, and describes
a length gauge’s capability to supply very
similar measured values for identical meas-
urands and conditions.
HEIDENHAIN ascertains the repeatability
of the length gauges with five measure-
ments near the lower plunger stop. The
plunger is completely extended and retract-
ed at medium speed. Since the length
gauge was already in operation for at least
10 minutes before this, it is already in a sta-
ble thermal state.
Repeatability
Series Repeatability
< x ± 2s
AT 1200 0.4 µm
AT 3000 0.8 µm
CT 2500 0.02 µm
CT 6000 0.03 µm
MT 101 0.04 µm
MT 1200 0.03 µm
MT 2500 0.09 µm
MT 60 0.06 µm
ST 1200 0.25 µm
ST 3000 0.7 µm
The repeatability of the length gauges is
usually better than the values listed in the
table. The characteristic statistical distribu-
tion is shown in the diagram, using the
ST 1200 as an example.
Repeatability depends on the
• combinations of materials used in the
components,
• installed electronics,
• optomechanics used, and the
• bearing of the plunger.
Fr
equency

Repeatability 
ST 1200: Statistical distribution of the repeatability