TB 9-4931-537-24
b. Intercomparisons
(1) Intercomparison checks will be performed on all reference level measurement
standards being calibrated by the equipment manufacturer, the APSL, or any other higher
level calibration activity.
(2) Calculate control limits (CL) as follows:
(a) List all possible contributors to measure error, including:
1 Test reported uncertainties or manufacturer's specifications (as
applicable) for standards being compared.
2 Estimated maximum drift of standards for the interval, if known from
history or manufacturer's specification (if applicable).
3 Test reported uncertainties or manufacturer's specifications for the
system used to compare the standards (if applicable).
(b) Ensure each contributor listed is in the same units of measurement, i.e., all
in kPa, inches, ppm, percent, etc.
(c) Add one additional contributor, equal to the largest of the previously listed
contributors, for unknown effects such as environmental.
(d) Combine all contributors using the root-sum-square method, where the
control limit (CL) is equal to square root of the sum of the square of each contributor.
CL = a
b
c
+
+
...
(2) When intercomparison of a measurement standard detects a defective standard,
the appropriate action(s) should be taken:
(a) Re-verify calculations for control limits.
(b) Determine which standard is defective by intercomparison with a third
standard, by direct measurement of the standards, or by other suitable techniques. When
it cannot be determined which standard is defective, the problem should be discussed with
the supporting calibration activity.
(c) Determine what caused the out-of-CL condition.
(d) Return the defective standard to the supporting calibration activity for
repair or re-calibration after the problem has been discussed with the supporting
calibration activity.
(e) For problems that cannot be resolved, or if assistance is necessary, contact
Commander, U.S. Army Aviation and Missile Command, ATTN: AMSAM-TMD-LW,
Redstone Arsenal, AL 35898-5000.
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