An instrument — such as my trusty Simpson 260 volt-ohm-milliammeter — doesn't require calibration because I use it for gross measurements. But engineers must calibrate lab instruments such as oscilloscopes, digital voltmeters and signal sources used for precise measurements. When a calibration comes due, an instrument — even a PXI or VXI plug-in instrument — goes to an accredited calibration lab. (I'll discuss calibrations more in another column.)
Although measuring-equipment manufacturers specify calibration intervals, typically a year or less, engineers might need to calibrate instruments at other important times, particularly:
When measurement values vary from what you routinely observe or when results seem unusual. These types of observations might signal a need for repair or a thorough clean-out of dust and grime followed by a calibration. Remember, components age so older equipment can need more frequent calibration than newer instruments.
When an instrument experiences rough handling or damage. If a pair of pliers falls on your sensitive DVM or source-measure instrument it shouldn't need calibration. But if the DVM drops off a shelf onto your bench, consider calibrating it. (If you send instruments off-site for calibration, pack them carefully and ensure the cal lab does the same.)
When you start a high-value project. You don't want to get deep into a prototype design only to find you've reported inaccurate test values. Of course you won't know you have bad values until someone tries to duplicate your results or a final design doesn't perform as expected. Some companies might recommend calibrating instruments at the end of such a project, too, just to verify the accuracy of your measurements. A cal lab typically provides a calibration report that includes "as received" information. If the instrument performs within spec, the lab won't perform the associated calibration. Labs also report measured "as sent" information so you know the state of your instrument when it left the lab.
When a contract stipulates instrument calibration. A contract between a company and a university research lab could require calibration of instruments at specific times or by a specific lab.
When production-test equipment produces too many false passes (bad products that test well) or false failures (good products that test bad). No company wants angry customers with faulty products or a rework line jammed with good parts awaiting unnecessary repairs and retesting. You can use statistical process-control (SPC) software to help detect false-pass and false-fail results.
As Sir William Thomson, Lord Kelvin, said, "If you cannot measure it, you cannot improve it." So ensure you keep calibrations up to date.
One way to keep a Formula One racing team moving at breakneck speed in the pit and at the test facility is to bring CAD drawings of the racing vehicle’s parts down to the test facility and even out to the track.
Most of us would just as soon step on a cockroach rather than study it, but that’s just what researchers at UC Berkeley did in the pursuit of building small, nimble robots suitable for disaster-recovery and search-and-rescue missions.
Design engineers need to prepare for a future in which their electronic products will use not just one or two, but possibly many user interfaces that involve touch, vision, gestures, and even eye movements.
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