Acceptances Sampling of Reliable Tubes

The traditional method of checking acceptability of a lot of tubes for a particular electrical characteristic has been to test a large sample and count the number of tubes beyond the minimum or maximum limits - inspection by attributes. This reduces the chances of accepting a lot with a high percentage of defectives, but gives no assurance that the lot is centered close enough to bogey or that the spread of the distribution is tight enough. The increasing complexity of circuitry and the high standards of performance required in many types of equipment have increased the need for such assurance. It is gained most simply from inspection by variables. Simply adding variables inspection criteria to the minimum and maximum limits already on the TSS will not do an efficient job of separating good lots from bad. By proper co-ordination of the two types of inspection, attributes and variables, a high degree of discrimination can be achieved with a modest amount of testing. Examples are based on recent TSS for type JAN 5744WA.