in this ppt we have talked about oc curve, its shape,calculation,characteristics and uses.

1. Operating Characteristics Curve
(OC Curve)
By
Apoorva modak &
Ashwini sakpal

2. Graph used in OC curve to
determine the probability of
accepting production lots
when using different sampling
schemes. It shows percentage-
defectives along the
horizontal ('X'), axis and
probability of acceptance
along the vertical ('Y') axis.
Lots having more than the
acceptable percentage of
defectives are rejected. Used
in Discrimination of Sampling
Plan Between Good And Bad
Lots.

3. TYPICAL OC CURVE:
 This is Curve Roughly “S”
Shaped.
 Obtained by joining
points between
Probability of
acceptance & Percentage
non conforming items.
 Obtained by Performing
Sampling Inspection.
Shape Of OC Curve
IDEAL OC CURVE:
 When percentage of Non-
Conforming items are Below
prescribed level Pa is 100%.
And more than it makes Pa
0%.
 Ideal OC Curve Can be
Obtained By 100% Inspection.
 Dividing line of Probability of
acceptance Between 0 to
100% is AQL

4. Ideal OC Curve
Typical Operating
Characteristic (OC) Curve
Ideal curve would be
perfectly perpendicular
from 0 to 100% for a given
fraction defective
Larger the sample size steeper
is the slope of OC curve

5. OC Curve Calculation
Hyper Geometric
Distributions
Poisson Distributions
 Used for sampling
plans involving the
number of defects or
defects per unit
rather than the
number of defective
parts.
 The probability of
exactly x defects or
defective parts in a
sample n:
 The hyper geometric
distribution is used to
calculate the
probability of
acceptance of
sampling plan when
the lot is relatively
small
,
P(X)= N-X X
C . C
n-x x
N
C
n

6.  Assumes a finite lot.
 Hyper geometric
distribution is used
for this type of curve.
 Binomial or Poisson
distribution often
provides a good
approximation.
Characteristics Ideal OC
Curve
Characteristics Typical
Operating Characteristic
(OC) Curve
 Assumes an infinite
lot.
 Binomial
distribution is the
correct one.
 Poisson
distribution often
provides a good
approximation

7.  Selection of sampling plans
 Aids in selection of plans that are
effective in reducing risk
 keeps the high cost of inspection
down
OC Curves Uses