The knowledge about the stability of the measurements in the test program is very important during the debug and acceptance phase. The window Numerical Statistics shows the stability, repeatability, process capability and measurement equipment capability of the test results.
This window shows multiple information at first sight:
Minimum value of the measurements
Maximum value of the measurements
Mean value of the measurements
Standard deviation
cp
cpk
cgm
cgmk
The foundation of the calculation is as follows
Average, standard deviation and variance
v ..................................................... test value
exec_cnt .......................................... test counter
sums ............................................... sum of test values
sqrs ................................................. sum of the square of the test values
average............................................ average
variance ........................................... variance
std_dev ............................................ deviation (only for exec_cnt>1, because division by 0 is not defined)
cp
hi_limit.............................................. high Limit
lo_limit.............................................. low limit
tolerance........................................... Test Tolerance
std_dev............................................. standard deviation
cpk
The cpk value documents the production process capability.
It shows which tests will have a high yield in the production. A cpk value, which reflects the quality of the lot, is assigned to each test. The average value has to be within the tolerance defined by the low and high limit.
The cpk value is called “critical” or “asymmetrical” process capability, because the average value is considered.
The process quality is good when cpk > 1.33.
hi_limit.............................................. high Limit
lo_limit.............................................. low limit
std_dev............................................. standard deviation
average............................................ average
variance ........................................... Variance
cpk .................................................. cpk (capability process key)
cgm
The cgm (capability gauge measurement) value documents the distribution of the measurement equipment.
The distribution is good when cgm > 1.33.
Execution of the measurement
• The measurement equipment has to be calibrated
• The measurement equipment can not be recalibrated during the test
• 1 golden device
• 25 .. 50 measurements
hi_limit.............................................. high Limit
lo_limit.............................................. low limit
std_dev............................................. standard deviation
tolerance........................................... Test Tolerance
variance............................................ Variance
cgm.................................................. cgm (capability gauge measurement)
cgmk
The value cgmk documents the distribution of the measurement equipment. It takes into consideration the nominal value of the test.
This value is important for correlation tests. .
hi_limit.............................................. high Limit
lo_limit.............................................. low Limit
tolerance .......................................... Test Tolerance
average............................................. average value
variance ........................................... Variance
std_dev............................................. standard deviation
golden_dev ....................................... value of the golden device
cgmk ................................................ cgmk
