The nP chart measures the number of nonconforming items in an inspection lot. It is identical to P chart except that the actual number of nonconforming items, rather than their proportion of the sample, is plotted. The inspection sample sizes must be equal in this case.
Data Available
N = Number of units produced in each sample ( subgroup size )
R(1..K) = Number of units rejected in each subgroup
K = Inspection Quantity
To be calculated :
Process Average Number Non conforming,
= 
Sigma (Standard deviation)
SNP =
Center Line and Control limits
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Center Line ( CLNP ) |
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Upper Control Limit (UCLNP) |
CLNP + 3 SNP |
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Lower Control Limit (LCLNP) |
MAX(0,(CLNP – 3 SNP)) |
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SPC chart calculations. |
