How often should you calibrate?

The question isn’t whether to calibrate, it’s how often to? There is no “one size fits all” answer. In most cases the requirements vary depending on application, QA requirements, industry standards, performance, or safety regulations. Calibration is often the key to negating a recall, out-of-tolerance condition, or potential safety concern.

There are a few possible points to consider when reviewing calibration frequencies to help you decide what is best for your process, equipment, and application.

Manufacturer-recommended calibration interval. Manufacturers’ specifications, which are usually located in the manual, indicate how often to calibrate their tools. Keep in mind that critical measurement applications may require different intervals, usually more frequent, stringent, or industry-defined (ASTM 2570, ISO 9000, ISO/IEC 17025, MIL-STD xxx).

Before a major critical measuring project. Suppose you are taking a plant down for testing, and that plant requires highly accurate measurements. Decide which instruments you will use for that testing and ensure those instruments are well within specification before using them. Send them out for calibration, then “lock them down” in storage so they are unused before the test. Calibrating before a critical measuring project is extremely important. If you will be making decisions or taking actions based on the measurement results, you’ll want to ensure with a high degree of confidence that the standards used remained in tolerance.

After a major critical measuring project. Just as it’s important to calibrate before a major critical measuring project, it’s important to calibrate afterwards. If you reserved calibrated test instruments for a critical test, it is best practice to send that same equipment for calibration after the testing. When the calibration results come back, you will know whether the tests done with the instrument were complete and reliable. In some industries, like pharmaceutical, calibrating before and after a major critical measuring project may be required. This ensures the reference used can show whether an intolerance condition occurred before, during, and after the critical measurement project.

After an event. If your instrument took a hit—for example, something knocked out the internal overload protection or the unit absorbed a physical impact--it is best practice to send it out for calibration to have the integrity checked. This is important because sometimes there may not be a visible physical defect on the unit like a dent, scratch, or broken connector. Calibration will verify that the unit and the critical internal components are in good working order.

Per requirements. Some measurement jobs require calibrated, certified test equipment regardless of the project size. Note that this requirement may not be explicitly stated but simply expected based on industry standards. Always review the specifications and requirements of a process before the test. The most common requirement is annual calibration, but this can vary dramatically depending on the application, industry regulation, or QA requirements.

Monthly, quarterly, or semiannually. If you do mostly critical measurements and do them often, a shorter time span between calibrations means less chance of questionable test results. Many times, calibrating at shorter intervals will afford you with better specifications. Users should look for trends in their calibrated equipment and periodically review, then note changes. As equipment gets older, for example, you may see the equipment drift before the next calibration cycle. Reviewing trends or year-over-year calibration results helps users understand when an instrument should be calibrated specific to your application and usage. Users may choose to calibrate instruments in shorter or longer cycles depending on the results they see over time.

Annually. If you do a mix of critical and non-critical measurements, annual calibration tends to strike the right balance between prudence and cost.

Biannually. If you seldom do critical measurements and don’t expose your meter to an event, calibration at long frequencies can be cost-effective.

Never. If your work requires just gross voltage checks (“Yep, that’s 480 V”), calibration seems like overkill. But what if your instrument is exposed to an event? Calibration allows you to use the instrument with confidence.