What is Metrology?
Simply put, Metrology is the science of measurement. This is the...
When you're doing work with tools of any kind, accuracy is important. This goes for even the simplest of measuring instruments, like tape measures. A calibrated tape measure ensures that you'll get a precise read each time. You should maintain a regular calibration schedule with each of the tape measures at any job so that measurements are consistent.
In this article, we'll cover everything you need to know about maintaining the accuracy of your tape measure. We'll look at how to calibrate a tape measure and why. Plus, we'll give you simple tips for fixing a tape measure that is not accurate.
If you were building something in a world where only you and your tape measure called the shots, then accuracy wouldn't matter so much. In that scenario, your measurements would be the only ones influencing your work. If you measured 1.1 inches instead of 1 inch for both the shelf and the wall, you could still have an accurate shelf installation.
However, that flexibility goes out the window in any instance with outside measurements. If you're working with a plan or blueprint or as part of a team, you need to be sure that all measurements adhere to an agreed-upon standard. That's the purpose of calibration — to get rid of bias in a measurement system.
Not all tape measures are identical. You may have three tools on the same job site that all read something different. If you want all your work to be precise, you need to match your measurement tools to the same standard through calibration.
Having the right tool for a job is only helpful if the tool is precise. Tape measures, like any other measurement instrument, can lose their accuracy over time. Some may not have been accurate, to begin with. If you want to do a job right (and of course you do!), it's essential to check the accuracy first with calibration.
When it comes to measurement, there will always be some degree of error, no matter how tiny. The goal is to make the error as small as possible. We do that through calibration. The process of calibration involves checking one measurement tool with another that is known to be more accurate. We continue comparing the accuracy of each instrument against a higher accuracy standard until we reach the highest possible standard.
The accuracy of a tape measure depends on two things: the markings and the ends of the instrument. Of course, the markings will be wherever the manufacturer puts them. They should be accurate, but different tape measures will be made to different standards of accuracy.
For this reason, there are three classes of accuracy for tape measures. Not all devices are certified by class, but those that will have the class printed on the tape. Class I is the most accurate and thus the most expensive, measuring within 1.10mm of accuracy in lengths over 10m. Class II is the most common and get within 2.30mm of accuracy for measurements over 10m.
Even if a tape measure is a Class I, and printed with the most accurate marks, it will still need to be calibrated sometimes. This is because of the second influence on accuracy — the end of the instrument. If the metal tip becomes bent or shifts out of place, it will affect the measurement.
The metal tip at the end of the device is a little loose on purpose. It's designed to adjust and provide a true zero, whether you're measuring by pulling against the hook or pushing it into a surface. For instance, if you're using a tape measure with a hook that is 1/16" thick, then the first inch of the tape will be 15/16". This way, if you're measuring with the hook against a surface, that additional 1/16" will create a complete inch. When you measure by pulling the tape, the hook should shift by 1/16" to provide an accurate inch.
This is a clever and simple way to provide both a push and pull measurement function. However, it's necessary to check that metal piece regularly through calibration. This way, you can ensure that it's moving in a way that keeps the tool's accuracy.
To calibrate a tape measure, you need a trusty tool with a clever name — a tape measure calibrator! This tool has a slot in it, where you will place the metal tab at the end of the tape. You can check both the push and pull measurements against the measurement marks engraved on the calibrator. Push and pull should each be equally accurate.
If the lines of the tape measure line up perfectly with the lines on the calibrator, you're good to go. Your instrument is ready for accurate measurements. If not, your tape measure is reading incorrectly.
There are several things you can do to troubleshoot an inaccurate tape measure. If you're finding that the pull measurement is inaccurate, but the push measurement is correct, you might be dealing with a bent tab. Look at the metal piece and adjust it with pliers if needed. Some tape measure calibration tools also come with a slot designed for adjusting the hook. Check again after adjustment using the calibrator and see if you've fixed the problem.
If the hook doesn't appear to be bent, you may notice a small bump or burr on the metal instead. This could be left over from when the piece was manufactured. Carefully file down any bumps and check the measurement again.
If your pull measurement is fine but the push measurement is messed up, it could be that something is stuck to the end of the tab. This may be an adhesive leftover from a project. Remove whatever may be there and recheck the measurements.
If you're still not getting accurate reads, look at the rivets holding the tab in place. They may be too loose and causing too much movement. You can adjust the tab with the calibration marks on your calibrator, then tighten the rivets using a hammer and a drift punch.
Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.
You have just purchased new measurement & test equipment and are ready to calibrate it. You...
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