What Is Guard Banding?

Guard banding refers to setting stricter tolerances when calibrating and assessing electronic equipment for various purposes, including quality control inspections. The practice of guard banding increases confidence that a product complies with the required specifications.

Setting the Limits

Determining what limits to set when guard banding is often based on how critical the measurements are, according to "Determination of Process and Calibration Tolerances and Correcting OOT Observations and Events with Appropriate Response" by Marcus McNeely. For example, in the aerospace industry, the limits are much stricter.

Test Accuracy Ratio

The challenge is to define a guard band so that it is appropriate in a given context. High Test Accuracy Ratio or TAR, defined as the ratio of the specification of a given parameter to the uncertainty of the instrument, is desirable, but costs more to the manufacturer or supplier.

Quality Control

While guard banding may result in a higher number of rejects, it reduces the number of unacceptable units that are shipped to customers. The supplier must weigh the cost of a higher rejection rate against the degree of customer satisfaction, according to "Differences in Guard Banding Strategies" by Marcello Lucano.

References

• Agilent Technologies: Differences in Guard Banding Strategies
• SiliconFarEast: Metrology and Calibration
• Blue Mountain Quality Resources: Determination of Process