HEIDENHAIN Length Gauges - Manual (Page 19)

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Gauging force – plunger actuation
Gauging force
Gauging force is the force that the plunger
exercises on the measured object. An
excessively large gauging force can cause
deformation of the measuring contact and
the measured object. If the gauging force
is too small, an existing dust film or other
obstacle may prevent the plunger from
fully contacting the measured object. The
gauging force depends on the type of
plunger actuation.
Plunger actuation by spring
For the AT 1218, AT 3018, MT 12x1, MT 25x1,
ST 12x8 and ST 30x8, the integral spring
extends the plunger to the measuring posi-
tion and applies the gauging force. In its
resting position, the plunger is extended.
The gauging force depends on the follow-
ing criteria:
• The operating attitude
• The plunger position, i.e. the force
changes over the measuring range
• The measuring direction, i.e., whether
the gauge measures with extending or
retracting plunger
In the diagrams, the measuring force is
shown over the measuring range for a
retracting and extending plunger in a
horizontal operating attitude.
The MT 1281 and ST 1288 length gauges
are available with various gauging forces.
Particularly for fragile materials this makes it
possible to measure without deformation.
The gauging forces can be divided into the
following classes:
• Reduced MR: Approx. half the gauging
force of the standard variant.
• Low MW: Gauging force at the
beginning of the measuring range,
approx 0.01 N
• Springless MG: Constant gauging force
over the entire measuring range
In order not to influence the gauging force,
the variants ST 1288 MR and ST 1288 MG
are provided without a rubber bellows. Due
to their low gauging force, the variants
MT 1281 MW, MT 1281 MG and ST 1288 MG
can only be used for measuring vertically
downward. For this reason, the diagram
shows only gauging forces for a vertical
operating orientation.
Plunger actuation by measured object
The complete length gauge is moved
relative to the measured object, normally
while the plunger retracts.
Gauging f
or
ce [N]

Distance [mm] 
MT 12x1 extending
MT 12x1 retracting
ST 12x8 extending
ST 12x8 retracting
AT 1218 extending
AT 1218 retracting
Gauging f
or
ce [N]

Distance [mm] 
MT 25x1 extending
MT 25x1 retracting
ST 30x8 extending
ST 30x8 retracting
AT 3018 extending
AT 3018 retracting
Gauging f
or
ce [N]

Distance [mm] 
MT 1281 MW extending
MT 1281 MW retracting
MT 1281 MR extending
MT 1281 MR retracting
ST 1288 MR extending
ST 1288 MR retracting
Plunger actuation via cable-type lifter
(MT 12x1, MT 25x1)
Through a cable mechanism, the plunger is
retracted by hand and then extended onto
the measured object. The measurement is
made with extending plunger.
The integral pneumatic damping reduces
the plunger extension speed to prevent
bouncing, for example on very hard materi-
als. This prevents measuring error through
bouncing.
Special variants 12 mm measuring range 25 mm/30 mm measuring range