MTS Axial Extensometers - Manual (Page 42)

Calibration 42
the full travel range of the transducer. (Full-scale ranges of 5% may be
possible, but some increase in drift and noise will result.)
In most transducers, the best linearity is obtained by setting the gain
between 70% and 90% of the desired travel range instead of 100%. The
adjustment procedures in this manual use 80% full scale as the reference
value.
Delta K
Delta K is a feature of DC conditioners manufactured by MTS Systems
Corporation. Delta K compensates for differences in symmetry between
the positive and negative outputs of the transducer. Gain is usually
adjusted to calibrate the compression half of the transducer range. Use
Delta K to calibrate the tension half of the transducer range.
Symmetrical versus Asymmetrical Extensometers
Typical extensometers may have only positive output (tension only), or
may have both positive and negative output (tension and compression).
It is also possible that the extensometer has asymmetrical travel (such as
+10 mm and -2 mm). It is important that you determine the full scale
travel range of the extensometer before proceeding.
For example
Suppose you have an extensometer with an asymmetrical travel of +10
mm and -2 mm. It is desired to adjust the conditioner to have a full-scale
output equal to the full travel range of the extensometer. In this case +10
mm would approximately equal +10 V, and -2 mm would have an
output of -2 V. Gain would be adjusted so that -2mm would yield -2 V,
and delta K would be adjusted so that +8 mm would yield +8 V while
adjustments to zero are made to keep the null position of the
extensometer at zero.
In all cases, the actual displacement should be used to determine the
calculated output.
Note It may be difficult to obtain a displacement value of exactly 80%
full scale. In those cases, find a displacement you can achieve
Actual Displacement
Full-Scale Range
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⎝ ⎠
⎛ ⎞ 10 V
× Calculated Output =