Electrical Test Instrument and Equipment Calibration

Companies and research labs using electrical test instruments are deadly serious about instrument calibration. They pay top dollar for high-end branded instruments, and it’s not unreasonable that they expect it to be calibrated to provide the extreme precision and reliability promised. The important questions to consider here are what is calibration, why electrical test equipment needs it, when it needs to be done, and how it is done.                  

We’re talking about the latest cutting-edge digital instruments with LED or LCD displays here. One would think it doesn’t have that many mechanical or moving parts that go out of whack.  You can’t open it up and tighten some screws or grease the works with a bit of lubricant. So exactly what does a metrology lab which handles test instrument calibration do?

Their job is to compare the instrument’s test results against that of a standard that is known to be at least 10 times as accurate as the instrument. After all, you can’t use a 100V voltmeter with an accuracy of three percent to calibrate another one with the same range and accuracy. If they show different readings, you have no way of knowing which one is accurate. In fact, both might be inaccurate.

What needs to be done is simple. Based on the results and the comparison against a more accurate standard, the metrology lab decides whether the instrument is “in-cal” or “out of cal.” If it is the latter, the parts and settings are adjusted until it provides a more accurate reading within the acceptable tolerance limit.

Then there’s the question of the test equipment calibration frequency, better known as the calibration cycle. The safest bet is to follow the manufacturer’s instructions as to how frequently you need to send it in for calibration. It would also be prudent to do so before a highly critical measurement, and also after overloads or hard knocks that may have disturbed the settings.

Some organizations ignore all this, and just follow their own calibration cycle to get all their instruments calibrated once a year, twice a year, quarterly, or on a monthly basis.

Note that not every kind of electrical test equipment needs to be calibrated. Some are classified by the manufacturer as "No Calibration Required" or NCR. This does not mean the instrument is an engineering marvel that never goes out of whack.

All it means is that the intended usage won’t be affected in any way by a bit of inaccuracy. An NCR classification is basically meant to assure the buyer and users that the instrument will perform its function effectively even without regular test instrument calibration and maintenance.