In addition to cleanliness, the temperature also has a decisive effect on the measuring result:
All parts made of all materials have different dimensions at different temperatures.
This is why specifying a dimension only makes sense if the temperature of the part is known as well. This is why a reference temperature of
68 F has been established. The standard ISO 1 have established that all dimensions given must refer to this reference temperature. This is why measurements must be taken at
68 F (20° C).
Even small deviations from the reference temperature of
68 F have significant effects: Materials become deformed and increase in size with increasing temperature. Thus, a piece of steel 1 m in length (at
68 F) will already be 11 µm longer at 70 F.
The following components must have a temperature of 20° C to allow a correct measurement:
This is why parts should be temperature controlled for at least 24 hours and stored in-between not outdoors. Nor should the metrologist touch the part with bare hands, since the body temperature of the metrologist will warm up the part. When cleaning, care must be taken not to warm parts and styli by friction.
A guiding principle to remember is:
The most important measuring device in length metrology is
the temperature sensor!
Note: For constant temperature deviations, software temperature
compensation is also possible. Its use requires good knowledge of the
specific possible errors!
68
F Reference temperature according to ISO 1 This temperature must be constant in the entire room and over time
