Anyone working in a manufacturing plant knows the horrible feeling when the person responsible for equipment calibration comes around looking at calibration stickers. More than once I've found myself trying to plead for an extra week, saying “I swear I'll bring it by before it expires, just let me finish this one thing!” And God help you if the unit has to be sent outside of the company for calibration – that takes forever! It's easy to ask why on earth calibration is such a big part of most MRO plans. And is sending it back a week late really that big of a deal?
After working at a measurement company and calculating error budgets, I can easily say that one extra week is not a big deal. But calibrating a unit on time is like changing tires when they get down to 2/32” tread. It probably won't be a problem, but if something goes wrong because you knowingly skipped cal you'll look a moron, especially in front of people like ISO auditors.
Each electronic component used in a design comes with its own large error that would make for a horrible specification. But the initial calibration at the factory takes care of that by adjusting the circuit or making calculations to account for initial error. So if a unit has already been calibrated, why does it need to be repeated every year? Unfortunately, all electronic parts continue to drift for all of time. Resistors, capacitors, op amps, transistors, diodes, everything. How do they change? Almost always in a logarithmic fashion like the one below (where x=1 is when initial calibration is completed):
What should you take away from this? First, that occasional calibration is indeed needed. Second, DON'T miss the first few calibration cycles! The older a unit is, the more stable all of the components have become. Plus, it's a great sanity check on the unit’s function since a calibration routine goes through the entire functionality to makes sure everything is up to snuff.
One fringe benefit from sending the unit back to cal: manufacturers collect that cal data like Google collects information on what you want to buy. It gets analyzed, poured over, and experimented with. Not only does this make sure that the calibration specifications are accurate, but engineers look at what improvements could be made to..... EXTEND the calibration intervals!
So take it easy on your local calibration coordinator. In the end they make possible for your equipment to do what you want, when you want, every time. As long as it isn't out for cal.