measurement systems analysis

Question 1

measurement system definition

Answer 1

is the collection of operations, procedures, measurement instruments, fixtures and other equipment, software, personnel, environmental conditions and assumptions used to assign a number to the characteristic being measures

Question 2

what does it mean to evaluate a measurement system?

Answer 2

to evaluate a measurement system means to examine its variation as well as the factors affecting it

Question 3

precise vs. not precise

Answer 3

• precise = close together (little variation)

- not precise = spread out (lots of variation)

Question 4

bias (inaccurate) vs. unbiased (accurate)

Answer 4

• biased = average is off target

- unbiased = average is on target

Question 5

the evaluation of measurement systems is done through…

Answer 5

through the stability, bias, linearity, repeatability, and reproducibility studies

Question 6

uses of measurement systems evaluation

Answer 6

• to accept a new measurement equipment (ME)
• to compare two ME
• to assess a dubious gauge
• to evaluate a gauge before and after repair

Question 7

repeatability definition

Answer 7

variation among repeated measurements performed by one operator to a single piece and with the same measurement equpiment

Question 8

test elements of repeatability

Answer 8

one gauge, one operator, one piece measures several times

Question 9

possible causes for low repeatability

Answer 9

measurement equipment - dirtiness, friction, not adjusted, worn out

Question 10

reproducibility definition

Answer 10

variation among the average measurements performed by several operators using the same pieces and the same measurement instrument

Question 11

test elements of reproducibility

Answer 11

one gauge, 2-3 operators, 10 pieces

Question 12

Gauge R&R- definition and steps

Answer 12

• combination of the repeatability and reproducibility studeis
• calibrate the gauge
• select 2-3 operators to measure at least twice the same 10 units in random order
• select the units in a way that cover all the spec. range and that some are outside of it
• fill in the GR&R format or use software

Question 13

if repeatability is poor compared to reproducibility, then possible causes are:

Answer 13

• gauge needs maintenance
• gauge should be redesigned to be more rigid
• improve the locations of the units
• there exists a large internal variation in the samples

Question 14

if reproducibility is poor with respect to repeatability, possible causes are:

Answer 14

• operator needs training in the use of gauge
• scale readings not clear enough
• possibly a fixture is needed

Question 15

ranges for % contribution

Answer 15

less than or equal to 1% means acceptable
greater than or equal to 10% means unacceptable
in between = marginally acceptable

Question 16

ranges for % tolerance

Answer 16

less than or equal to 10% means acceptable
greater than or equal to 30% means unacceptable
in between = marginally acceptable

Question 17

Number of distinct categories in minitab gauge r&r

Answer 17

the number of groups your measurement tool can distinguish from the data itself - this is the discriminating capability of the measurement instrument - acceptable is >= 5

Question 18

% Contribution: what each means

Answer 18

• Total Gauge R&R: amount of variation due to Gauge R&R
• repeatability: variation due to repeatability or measuring equipment
• variation due to reproducibility or operators
• Part-to-Part: part-to-part variation