DH Instruments COMPASS FOR MOLBOX, Руководство пользователя

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COMPASS
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for molbox™ User’s Manual
Page 193
© 1998-2003 DH Instruments, Inc .
If the minimum and maximum reference flows in the test sequence are equal, linearity cannot be
calculated and COMPASS displays <N/A> in place of a number.
19.9 HYSTERESIS
COMPASS determines the hysteresis of DUT output relative to the reference readings. The hysteresis
value is included in the <Calculations> section of the Data File (see Section 18.4).
COMPASS first analyzes the test data to determine if a meaningful hysteresis calculation can be made.
For hysteresis to be calculated, the test flow sequence must correspond to a normal ascending and
descending (or vice versa) calibration sequence. This means that the first and last nominal flow points
must be the same as well as the second and second to last, etc. If the sequence does not meet this
criterion,
COMPASS displays <N/A> in place of a number. This is the same test used to determine which
type of linearity calculation will be used (see Section 19.9).
Hysteresis is the maximum difference between corresponding ascending and descending DUT flows in a
test point sequence. The hysteresis value is expressed in %DUTFS.
19.10 REPEATABILITY
A calculated repeatability value is included in the <Calculations> section of the Data File whenever a
multi cycle test is executed. The value is determined by comparing data from each test cycle and finding
the maximum error deviation between any two cycles at the same point. The value is expressed in
%DUTFS. Single cycle tests never include a DUT repeatability value.
19.11 MEASUREMENT UNCERTAINTY
The DUT measurement uncertainty resulting from the test is calculated as the root sum square of the
various components that determine the overall system uncertainty. This includes: linearity, hysteresis,
repeatability, resolution and reference uncertainty. DUT resolution is obtained from the DUT Definition
[Range] tab (see Section 8.5). DUT linearity, hysteresis and repeatability are calculated from the test
data (see Sections 19.8, 19.9, 19.10). Reference uncertainty is obtained from the [Reference] Hardware
Definition (see Section 10.3.3). Each of the values is converted to a single standard deviation by dividing
by the appropriate value. The final measurement uncertainty value is then multiplied by 2 to obtain a
coverage factor of 2. The uncertainty value is converted to %DUTFS for reporting. The calculation
described below determines the value in the DUT’s flow unit of measure. The measurement uncertainty
equation is described below. A full description and analysis of each of the measurement uncertainty
components is beyond the scope of this manual (see ISO/TAG 4WG3 Guide to the Expression of
Uncertainty Measurement).
COMPASS determines measurement uncertainty for each test cycle
individually as well as for all test data combined. The complete test data determination is found in the
final statistics section of the data file.
2
2
2
3
* 2
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+
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+ =
std resolution
EstErr DUT
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