Attribute controle, measurement control

Attribute control

Each part is measured according to a the OK/KO scale, acceptance of the batch is carried out if the number of KO’s measured is less than the limit.  Attribute control can be:

  • Single: a certain number of parts is measured once and the acceptance of the batch is defined at the end of the measurement of all parts.
  • Double: a first batch of parts is measured, the batch is accepted if the number of defects is less than “Acceptance 1”, rejected if the number of defects is more than “Rejected 1”, otherwise a second batch of parts is measured and the batch is accepted if the number of defects is less than “Acceptance 2”, otherwise it is “Rejected”. This type of control limits the number of parts being measured.
  • Progressive: the acceptance or rejection of a batch is calculated for each measurement. This type of control is the most effective.

Advantage of attribute control: simple to set up

Disadvantage of attribute control: doesn’t allow an NQA of less than 1% without significantly increasing the number of parts being measured.

Measurement control  

Each part is measured on a quantitative scale, acceptance of the batch occurs if the batch’s mean is farther from the k standard deviation of the closest tolerance (k or k factor defined by the reception control). Measurement control can be:

  • Single: a certain number of parts is measured once and the acceptance of the batch is defined a the end of the measurement of all the parts.
  • Progressive: the acceptance or rejection of a batch is calculated for each measurement. This type of control is the most effective.

Advantage of attribute control: significantly limits the number of parts being measured in comparison with attribute controls.

Disadvantage of attribute control: Requires the measurement of each part quantitatively.