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3.4 Checking the Measuring Accuracy
All tension meters are calibrated with standard materials - such as polyamide monofila-
ment (PA) - according the SCHMIDT factory procedure. The filament sizes are noted in
Chapter 2. Any difference in process material size and rigidity from the standard material
may cause a deviation of the accuracy. In 95 % of all industrial applications the SCHMIDT
calibration has been proven to provide the best results and is used for comparative pur-
poses. If the process material differs significant in size, rigidity and shape we recommend
special calibration using customer`s sample. For this purpose a material sample of 5 m
should be supplied.
Checking procedure
:
- Suspend a known WEIGHT that corresponds to the tension to be measured (pay
attention to the correct unit of measure) from the PROCESS MATERIAL, vertically, as
shown in fig. 3.4. (Always use a fresh portion of the material to be measured).
- Push the THUMBPIECE as far as it will go in the direction indicated by the arrow and
thread the material to be measured between the GUIDE ROLLERS and the
MEASURING ROLLER. Refer to Chapter 3.2
- Slowly release pressure on the THUMBPIECE until the GUIDE ROLLERS return to their
original position.
It is essential that the THUMBPIECE return slowly to its initial position.
Any uncontrolled snap-back may affect calibration and may also damage
the instrument.
- Before the final check, move the instrument slowly up and down to compensate any
friction caused by the instrument and thus ensure the repeatability.
- The tension value should be equal to the value of the suspended WEIGHT.
If this procedure shows a deviation beyond the allowable tolerance and a reliable
operation is no longer allowed, the instrument has to be recalibrated or repaired.
For recalibration, return the tension meter to the factory.
MEASURING
ROLLER
GUIDE
ROLLERS
WEIGHT
SCALE
THUMBPIECE
MEASURED
MATERIAL
FILAMENT
GUIDE
PROCESS
MATERIAL
GUIDE
ROLLERS
FILAMENT
GUIDE
FIG. 3.4