Compare an inspection gauge's resolution with a metal dimensional tolerance and determine whether the instrument meets the selected resolution screening criterion.
Gauge resolution is the smallest increment that an inspection instrument can display or distinguish according to its specified resolution. It is one of several characteristics that should be considered when selecting equipment for metal dimensional inspection.
For example, an instrument with a resolution of 0.01 mm can distinguish displayed increments of 0.01 mm, while an instrument with 0.10 mm resolution provides much coarser displayed increments.
When a manufacturing tolerance is tight, a coarse measurement increment can make it difficult to observe relatively small dimensional changes.
The calculator compares the gauge resolution with the entered tolerance. The selected criterion determines the maximum resolution considered acceptable for this preliminary screening calculation.
For a 1:10 criterion, the gauge resolution should be no more than 10% of the effective tolerance.
A 1:10 screening criterion means the gauge resolution is limited to one-tenth of the effective tolerance, or 10%.
For example, with a ±0.10 mm tolerance, a 1:10 screening criterion gives a maximum resolution of 0.01 mm.
This is a practical screening calculation rather than a universal requirement. The appropriate measurement capability depends on the inspection specification and measurement-system requirements.
The appropriate criterion should be selected according to the quality system, inspection procedure or engineering requirement governing the measurement.
Resolution and accuracy are different characteristics. Resolution describes how finely an instrument can display or distinguish measurements. Accuracy describes how close the measurement is to the true or accepted reference value.
An instrument can have excellent resolution but poor accuracy. Therefore, a resolution check alone cannot establish complete measurement suitability.
Repeatability describes how consistently an instrument produces results when the same characteristic is measured repeatedly under the same conditions.
A gauge may have fine resolution while still showing excessive measurement variation between repeated readings. Resolution should therefore be considered together with repeatability and other measurement-system characteristics.
Calibration establishes the relationship between an instrument's readings and reference standards. A gauge should remain within its required calibration condition regardless of how fine its display resolution is.
As a manufacturing tolerance becomes smaller, the required measurement resolution generally becomes finer when using the same screening criterion.
This relationship is important when selecting inspection equipment for precision machining and other processes with narrow dimensional requirements.
A dimensional measurement system is more than the gauge's displayed resolution. Fixture stability, operator technique, environmental conditions, calibration, repeatability, reproducibility and instrument accuracy can all influence the result.
For critical characteristics, a formal measurement-system analysis may be appropriate instead of relying only on a resolution-to-tolerance comparison.
This tool performs a gauge-resolution screening calculation. It does not determine complete measurement-system capability or certify that an instrument is suitable for a particular inspection.
The selected 1:10, 1:5, 1:4 or 1:2 criterion is only a screening basis. Actual requirements can be defined by company procedures, customer specifications, applicable standards or measurement-system analysis requirements.
What is gauge resolution? It is the smallest measurement increment an instrument can display or distinguish according to its specified resolution.
Is resolution the same as accuracy? No. Resolution describes measurement increments, while accuracy concerns closeness to a reference or true value.
What does 1:10 mean? It means the gauge resolution should be no more than 10% of the effective tolerance for this screening calculation.
Can a gauge have fine resolution but poor accuracy? Yes. Resolution alone does not establish measurement accuracy.
Can this tool be used for metal thickness? Yes. Enter the applicable thickness tolerance and the resolution of the thickness measurement instrument.
Does PASS mean the gauge is fully qualified? No. It means only that the entered resolution meets the selected numerical screening criterion.
What else should be checked? Accuracy, calibration, repeatability, reproducibility, measurement range, environment and measurement method should also be considered.