We purchase instruments for back-up purposes (in case something goes wrong with the current instrument being used). We conduct audits every 4 hours using this instrument. Should something go wrong with the current instrument and we do not have the backup, we are out of compliance. If we purchase the backup and we end up not having to use it, the calibration expires with it sitting on the shelf. How is this handled in other locations?
bwatkins 4/5/2005
One option would be to start with the established sampling plans, like the old MIL-STD-105, but which has more or less been replaced by ANSI-Z1.9 (available through ANSI or ASQ). This will give you sample sizes for fixed lot sizes or for continuous sampling, and allow you to throttle back to a reduced sample plan or ramp up to tightened, depending on what you experience.
dyancey 3/15/2005
Some criteria that comes to mind would be historical data from the particular machine and the risk associated with nonconforming materials being produced.