MIL-DTL-8971F
TABLE II. Electrode repeatability criteria.
This procedure shall be used to determine if electrodes pass repeatability requirements.
First, use the following formula to calculate the Repeatability Index (RI) for each element at each
applicable concentration level for both the candidate and the reference electrodes (see 3.9 and
4.6.2.6):
(N(∑ X ) - (∑ X ) )
2
2
i
i
RI =
N(N - 1)
where N is the number of analyses (normally 10), ΣX i 2 is the sum of the squares of the test
results in ppm of the N analyses, and (ΣX i) 2 is the square of the sum of the same test results.
Second, compare the RI value for the candidate electrodes to the corresponding tabulated value.
Third, if needed, statistically compare the RI values of the candidate and reference electrodes
using an F-test (see 4.6.2.6b).
If the candidate electrodes' RI value is equal to or less than the tabulated value, or if the
statistical comparison between the RI values indicates the candidate electrodes are equal to or
better than the reference electrodes, the candidate electrodes pass the repeatability requirements
for an element at a specific concentration.
To pass repeatability requirements for this specification, the candidate electrodes must pass the
repeatability requirements for all elements at all applicable concentrations.
Al, Cr,
Cu &
Ag &
Na
Pb
Sn
Ti
B
Zn
Y
Fe
Ni, & Si
Mg
Mo
5
0.56
0.64
0.56
0.56
0.64
0.95
1.04
0.58
0.58
0.78
30
1.58
2.45
1.58
1.58
2.45
2.01
2.06
1.87
1.87
3.63
100
5.03
8.02
5.03
5.03
8.02
6.07
6.08
6.02
6.02
12.00
300
24.00
24.00
15.00
27.00
48.00
18.00
18.00
18.00
18.00
36.00
N/A1
500
40.00
25.00
45.00
80.00
30.00
30.00
30.00
30.00
60.00
900
72.00
N/A
N/A
81.00
144.00
54.00
N/A
N/A
54.00
108.00
1
N/A = Not Applicable
7
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