Metrology, or the science of measurement, is a critical component of any skilled task, such as sewing, carpentry, metalwork, engineering, and architecture, all of which require tools to measure and the ability to interpret the measurements. They differ not only in the materials and tasks, but also vastly in the tolerance and resolution required to measure them.
| Tools | Distance | Resolution (Imperial) | Resolution (Metric) |
|---|---|---|---|
| Tape Measure | x feet/meter | typ. +/- 1/16" | typ. +/- 1mm |
| Steel Ruler | x inches/mm | typ. +/- 1/32" | typ. +/- 1mm |
| Caliper | x inches/mm | typ. +/- 0.001" | typ. +/- 0.05mm |
| Micrometer | in/mm | typ. +/- 0.001" | typ. +/- 0.01mm |
| Vernier Mic | in/mm | typ. +/- 0.0001" | typ. +/- 0.005mm |
Measuring Tools in Precision Maintenance
Precision in industrial maintenance requires many measuring tools, such as:
| Tools | Tools 2 | Tools 3 | Tools 4 |
|---|---|---|---|
| • Tape Measures | • Calipers | • Micrometers | • Dial Indicators |
| • Balancing Tools | • Laser Tools | • Multimeters | • Pyrometers |
| • Accelerometers | • Infrared Cameras | • Leak Detectors | • Levels |
Understanding Measurement Tool Accuracy
NO MEASURING TOOL IS 100% ACCURATE – there will always be slight variances in measuring tools.
- (2) 25-foot tape measures, when fully extended, may exhibit slight differences in length.
- The line marks on a tape measure may be 0.010” or more wide, with a good amount of “empty space” between marks.
- A micrometer without a vernier scale will also have a good amount of empty space between thousandths of an inch.
- Measuring tools with higher resolution can be influenced by factors such as temperature, vibration, surface finish quality, and inadequate calibration.
For example, a tape measure is an accurate tool for building a house, cutting a length of pipe, or hemming a pair of jeans. However, it is woefully inadequate for determining a shaft diameter and bearing bore, grinding prescription glasses, or checking the thickness of a mechanical heart valve. The degree of precision required for a measurement is based on the tolerance, or the allowable range of error, the resolution, or the smallest quantity the tool can measure and display, as well as calibration. Has it been checked and verified to measure to the degree of accuracy stated?
Keeping Measurement Tools Reliable
When performing maintenance, the technician needs to be mindful of:
- The tool – its range, resolution, and degree of accuracy,
- The tolerance – how much above or below “exact” is sufficient for the measurement,
- The calibration – has the tool been checked to ensure the measurement is sufficiently accurate for the measurement task?
Keep your laser alignment tools calibrated to ensure they measure accurately.
