Page 69 - Lehrbuch Neigungsmessung deutsch 2018.indd

COMPENDIUM INCLINATION MEASUREMENT
WYLER AG, WINTERTHUR / SWITZERLAND

6.4.4 INFLUENCE DUE TO THE TEMPERATURE DIFFERENCES BETWEEN THE INSTRUMENT

AND THE OBJECT TO BE MEASURED

Temperature differences within the workpiece or between the workpiece and the measuring base have a
great influence on the accuracy of the measuring results. The following chapter deals with some of these
related problems.
A temperature difference between the measuring base and the object to be measured causes a heat
flow. The amount of such a heat flow depends on the area of contact, the difference in temperature,
the materials of base and object as well as on the base
length and the cross-section of the measuring base.
In the base a temperature lamination occurs, which
bends and warps the base because of material expan-
sion. This results in constantly changing the area of
contact, which in turn changes the flow of heat. Con-
sequently, the measuring base is constantly in motion
until temperature equivalence is achieved. These parti-
ally brisk motions can be observed by the continuously Heat flow
changing of the instrument‘s display value.
The temperature dependant volume changes of the
base itself are also visible in the instrument‘s display Measuring
value. object
Important:
• Before conducting of a precision measurement, the temperature of the instrument and the object
must be checked.
• The time for temperature acclimatization of the instrument‘s base depends on the temperature
difference and the material used and will take between 30 minutes and 2 hours.

Influence of temperature differences within the measuring object
The influence of the temperature difference within a measuring object can be demonstrated with the
formula applied for calculating the deviation from flatness of a Diabas granite surface plate. The formula
is valid for stable conditions only and deals with the difference of temperature between the bottom of the
plate and the top of the plate.

D * a * L 2
Deviation from straightness (X) X = in [m]
T
8 * B

D : Temperature difference between top and bottom of the plate in deg. Kelvin
T
a: Coefficient of expansion of granite in (m) per deg Kelvin (5.6 * 10 [m/°K])
-6
L: Length of the plate (m)
B: Thickness of the plate (m)

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