USTER HVI SPECTRUM, Инструкция по эксплуатации, Страница: 46 / 230

USTER
® HVI SPECTRUM
Instruction Manual
Uster Technologies, Inc. Chapter 4
Calibration • Page 4-2
2
Cotton Calibration
To better understand the theory behind calibration procedures, it is
important to know the instrument/software principles of calibration.
Calibration is performed following engineering principles using
hardware devices. Adjustments are then made within the instrument to
the unadjusted, raw values through software manipulations. These
adjustments cause the test values to agree with designated values of
laboratory cotton samples. In this sense, the word “calibration” refers
to the adjustment of
values
rather than to true calibration.
Adjusting the values is accomplished by a two-point regression
analysis of individual test data points. The mathematics of the simple
regression will show relationships defined by “slopes” and “offsets.”
If, by chance, the unadjusted values of the instrument tests agree
exactly with the designated values of the two-calibration cottons, the
software “slope” will be 1.0 and the “offset” will be zero. However,
this perfect agreement will rarely ever exist.
In order for measured values to agree with designated values of
calibration cottons, slopes and offsets are calculated from tests
performed during calibration, and comparisons are made with the 1.0
slope/zero offset conditions. This results in corresponding adjustments
to obtain agreement between measured values and designated values
of calibration cottons.
If conditions such as calibration cotton samples, operator techniques
and procedures, and fiber moisture content (temperature and relative
humidity of laboratory air) do not change, the slopes and offsets that
were obtained from the initial calibration do not need to be changed.
The long-term stability in testing will exist.
The objective of calibration is to have slopes and offsets remain
constant for long periods of time. This is achieved through
management of laboratory conditions, following accepted procedures
and techniques, and performing routine instrument maintenance and
calibration checks.