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Every type of expert has a tool that they rely on each day. A writer relies on their laptop, a mechanic turns to their wrench again and again, and an electrician has their trusty multimeter. Like any other frequently used tool, a multimeter needs maintenance to keep it working well. In the case of any measurement instrument, a big part of that maintenance is calibration.
Multimeters need to be calibrated properly to ensure their accuracy with every use. Since multimeters are used to measure more than one electrical property, their calibration needs to address each of these processes.
Calibration is an essential service for all measurement technology. For every industry, measurements need to be accurate, and they need to fit an agreed upon standard.
During calibration, we use calibration standards to take a measurement. These devices are measurement tools that are used to give a known, accurate reference. Next, we take the same measurement with the device that is set to be calibrated. We call this the devices under test. This side-by-side comparison allows us to check the accuracy of the device under test against the calibration standard.
There are two main purposes of calibration. The first is, as mentioned, to test the accuracy of a measurement instrument. It goes without saying that getting accurate measurements from an instrument like a multimeter is essential to its purpose. A technician would have a hard time avoiding needless mistakes if they were getting incorrect readings on voltage or resistance.
Calibration also serves to provide guidelines for repairing an instrument that is out of calibration. A proper calibration will expose how an instrument’s measurement is off. Having the service of a calibration lab is a must when it’s time to fix instruments that have measurement errors.
To test the accuracy of a multimeter or other instrument, we use a calibration standard that is more accurate than the instrument we are testing. A standard should be three to ten times more accurate than the device under test.
Because we need to ensure the accuracy of a calibration standard, we must calibrate those as well. The calibration standard itself becomes the device under test, and another, more precise calibration standard checks its accuracy. This new calibration standard is tested with another, even more accurate standard. We continue this pattern as we move up towards the SI standards, also known as the International System of Units.
The SI is the modern metric system. It is internationally accepted, and as such serves to keep all measurement tools accurate to the same degree. Calibration labs work up to the SI standard through a process called traceability. Traceability is a chain of measurements that increase in accuracy until they reach an SI unit. Through the process of traceability, all labs can calibrate their instruments to meet the international standards. This keeps all measurements accurate to one another across the globe.
The concept of traceability is thousands of years old. It’s thanks to this practice that technicians can be sure their measurements will match the measurements of any other technicians following the SI standards for calibration. To be an accredited calibration laboratory, a lab like Alliance Calibration must be able to show its traceability.
Multimeters need calibration as much as any other instrument. These hand-held, digital devices will lose accuracy over time for several reasons.
Since multimeters are designed with electrical components, many conditions could affect how quickly they decrease in accuracy. Extreme temperatures and humidity can and will have an impact on the multimeter’s performance. For this reason, it’s important to store multimeters in a dry place, away from extreme heat or cold. Many multimeters have a case to help protect them when not in use. All should have directions on how to best store them.
Even if you do take care to keep your multimeter in a safe space, it will still need to be calibrated from time to time. Elements outside of temperature and humidity can affect accuracy as well, including low batteries and line voltage.
Hunter S. Thompson is quoted as saying, “Anything worth doing, is worth doing right.” That’s certainly true when taking any kind of technical measurement. If you’re working with a multimeter that’s out of calibration, it’s going to mess up your entire project. It’s absolutely necessary to have any measurement tool — including a multimeter — calibrated regularly.
Because of the many measurement capabilities in a multimeter, this instrument requires several calibration steps. A lab will test each of its features, including voltage, resistance, current, continuity, and frequency. It’s important that each element be tested against a calibration standard in an accredited calibration lab.
There’s never one-size-fits-all schedule for calibration, no matter the instrument. Different factors, such as storage conditions and use cases, well influence how often an instrument should be calibrated.
With most new measurement instruments, you should find a recommended calibration schedule in the manual. For a multimeter, most manufacturers suggest sending the tool off to a calibration lab once a year. Some, however, recommend more frequent calibration, sometimes as often as every 90 days.
The more often you have your multimeter calibrated, the more accuracy you can expect. As such, the type of work you’re doing with a multimeter also influences how often you should get it calibrated. If you need optimum accuracy at all times, you’ll want to follow a strict calibration schedule. But if you’re just a hobbyist, you could wait much longer in between calibrations.
With so many online resources available, it is possible to calibrate your own multimeter. However, this is only a good idea if you fall into the hobbyist category, where perfect accuracy isn’t necessary.
For those who are using a multimeter to work on professional equipment, it’s better to trust a specialist. Professional labs like Alliance Calibration are committed to maintaining high calibration standards. By investing in a professional calibration, you’ll avoid wasting time and money through an error in measurement.
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.
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