Oliver 75 - 3rd Question Control limits

bhuvanpanwar1983
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Oliver 75 - 3rd Question Control limits

Postby bhuvanpanwar1983 Mon Oct 05, 2015 9:37 am

A production process has been defined as part of an industrial equipment manufacturing project. The process is intended to produce steel bolts with a length of 20 cm. The control limits are 19.955cm and 20.045cm.
The measurements made at the end of the process yielded the following results:

20.033cm, 19.982cm, 19,995cm, 20.006cm, 19.970cm, 19.968cm, 19.963cm, 19.958cm, 19.962cm, 19.979cm, 19.959cm.

What should be done?

A The process is under control. It should not be adjusted.
B A special cause should be investigated, the process should be adjusted.
C The control limits should be adjusted.
D The measuring equipment should be recalibrated.

The question is from Oliver - and the answer is option B but why ? all the range above is between the control limit then answer should be "A"
pls somone help here.
ujjal_show
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Re: Control limits - Quality

Postby ujjal_show Mon Oct 05, 2015 10:12 am

seven consecutive plot points are 19.970cm, 19.968cm, 19.963cm, 19.958cm, 19.962cm, 19.979cm, 19.959cm below the mean.

A process is considered out of control when, seven consecutive plot points are below the mean.
bhuvanpanwar1983
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Re: Control limits - Quality

Postby bhuvanpanwar1983 Mon Oct 05, 2015 11:44 am

are you taking the point to 1 decimal point only? then you right, its 7 consecutive point. and option B is right answer.
ujjal_show
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Re: Control limits - Quality

Postby ujjal_show Mon Oct 05, 2015 12:45 pm

no, I am taking three decimal point between 19.955cm to 20cm.

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