Knowing the Basics of Digital Multimeter Calibration
Knowing your digital multimeter and its function may be enough, but it is also important that you have an idea on how it is being calibrated, and how the proper digital multimeter calibration can ensure your work quality.
A digital multimeter (DMM) is one of the most commonly used pieces of test and measurement instrumentation. Quality processes depend on its continual proper operation. However, time, environment, and physical use (or abuses) change a DMM’s characteristics. Therefore, it’s important to periodically calibrate or verify the performance of a DMM.
Calibration confirms that the multimeter’s performance meets the required specifications. The specifications can be the standard figures published by the DMM’s manufacturer, or they can be customized based on an organization’s needs. In general, the more precise and accurate a multimeter is, the more complex the specifications will be.
The calibrator you choose for the job should have these qualities:
Its specifications should be at least four times better than the specification of the DMM it is testing.
Its functions need to cover the functions of the DMM it calibrates. DMMs have at least five functions, with many ranges per function. The calibration procedure needs to confirm that the DMM is suitable to use through this full range of capabilities.
Often the DMM’s manual will recommend functions and minimum specifications necessary to calibrate the DMM properly. The manufacturer should provide all the test points and pass/fail limits as evaluated against their specification.
Sequences of calibration
Depending on the “as received” calibration state of a DMM and the customer’s requirements, there are three different sequences of operation that could be performed. The third sequence is the most common and most valuable for calibration customers.
- Calibration only (no adjustments made)
- Adjustment first; post-adjustment calibration (as left data)
- Pre-adjustment calibration (as found data); adjustment; post-adjustment calibration (as left data)
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Source: Understanding the basics of digital multimeter calibration