A pre-determined maximum force is applied to avoid tearing the foam backing. Most samples do not fail, so it is known only that the bond strength exceeds the pre-determined force. That is, the bond strength data are censored. The process is monitored by selecting samples across the width of the material at a given frequency based on the amount of material produced. The purpose of the monitoring is to ensure that the bond strength does not deteriorate.
Deterioration includes decreases in the average strength or increased variability.
A second example, which we do not consider in detail here, is the use of plug gauges to monitor hole size. To measure hole diameter, two plugs machined to have diameters at the upper and lower specification of the hole diameter are applied. If the larger plug enters the hole, then the diameter exceeds the upper specification. If the smaller plug does not enter the hole, then the hole size is below the minimum specification. For the purpose of process monitoring, the actual diameter of the few holes that fail are measured.