HEIDENHAIN Length Gauges - Manual (Page 17)

17
Design of ST 1200
Connecting cable
Measuring standard
Scanning unit with light
source, photocells and
scanning electronics
Ball-bush guide
Plunger
Rubber bellows
Measuring contact
Design of CT 6000,
MT 60
Measuring standard
(scale)
Holder
Scanning unit with light
source and photovoltaic cells
Ball-bush guide
Plunger
Measuring contact
HEIDENHAIN length gauges function
according to the Abbe measuring
principle, i.e. the measuring standard and
the plunger are exactly aligned. All
components comprising the measuring
loop, such as the measuring standard,
plunger, holder and scanning head are
designed in terms of their mechanical and
thermal stability for the highest possible
accuracy of the length gauge.
The plungers of the HEIDENHAIN length
gauges are locked against rotation. Their
optimally round form stays unchanged
while stability and thermoconductivity
remain unimpaired. They are provided with
an M2.5 thread to hold measuring contacts
(see Accessories)
The plungers of the HEIDENHAIN-ACANTO
and HEIDENHAIN-SPECTO ST 1200 length
gauges are protected by a rubber bellows.
The bellows are characterized by high re-
sistance to chemical and thermal influenc-
es and have a relatively low stiffness. Its
influence on the gauge’s mechanical be-
havior and the measuring force is therefore
low.
Setup
Thermal characteristics
HEIDENHAIN length gauges have a de-
fined thermal behavior. Since temperature
variations during measurement can result
in changes in the measuring loop, HEIDEN-
HAIN uses special materials with low coef-
ficients of expansion Þ
therm
for the compo-
nents of the measuring loop, for example
in the HEIDENHAIN-CERTO length gauges.
The scale is manufactured of Zerodur
(Þ
therm
 0 K
–1
), and the plunger and holder
are of Invar (Þ
therm
 1 x 10
–6
K
–1
). This
makes it possible to guarantee its high
measuring accuracy over a relatively large
temperature range.
Acceleration
Length gauges from HEIDENHAIN feature
a sturdy design. Even high vibration and
shock loads have no negative influence on
the accuracy.
However, shock and vibration of any kind is
to be avoided during measurement so as
not to impair the high accuracy of meas-
urement. The maximum values given in the
specifications for shock and vibration apply
to the effect of external acceleration on the
length gauge. They describe only the
mechanical stability of the length gauge,
and imply no guarantee of function or
accuracy.
In the length gauge itself, unchecked
extension of the spring-driven or non-
coupled moving plunger can cause high
acceleration onto the measured object or
measuring plate surface. For the MT 1200
and MT 2500 series length gauges, use
the cable-type lifter whenever possible
(see Accessories). The cable lifter features
adjustable pneumatic damping to limit the
extension velocity to an uncritical value.