This is an age old question with many
different answers, depending on who you ask.
And for those of you who may be confused, go ahead and stay confused,
because there really are numerous meanings of ‘Calibration.’
I saw a job ad recently for
Calibration Managers at a major tech company. In that instance, they were
hiring people to adjust customer perceptions (nothing to do with instrument
accuracy). Military applications include gun calibrations which adjust for wind,
distance, etc., until the projectile hits the target. Even within the metrology world, there are
different opinions about ‘Calibration’
versus ‘Verification.’ To some,
calibration is an adjustment, but not just a verification.
A simple definition of ‘Calibration’ when speaking of measuring
instruments is to measure the accuracy of your instrument against instruments
of known and higher accuracy, and adjust it as needed, to assure that it
conforms to its specifications over its full range of operation.
Whenever an instrument makes a
measurement of an internationally accepted value (such as volts DC or AC, Ohms,
Hertz, centimeters, degrees Celsius, PSI, kilograms, etc.), calibration
compares the accuracy of the measured or generated value of the instrument
against those international units. And if your instrument doesn’t match those
units, it is adjusted until they match (although some instruments don’t have
the ability to be adjusted).
This is an important detail that
many don’t well understand. Whether you’re measuring lengths to install a
window, weighing produce at a grocer, pumping gasoline, monitoring steam
pressure at a power plant, torqueing lug nuts on a tire of a car, or so many
other examples, the instrument making the measurement has to be right.
For all of the measured things we
all use every day to work together, they have to match. You measure a window
frame with a ruler or tape measure to make sure its dimensions are correct, so
that when you install a pre-fabbed window, it fits correctly. The manufacturer
of the window at some point used calibrated instruments to make it the right
size. And your tape measure or ruler were at some point compared to the same
internationally accepted units to make sure they measure accurately – to make
sure they matched the window.
This is what calibration really
is. It is making everyone’s measurements match.
The accuracy of all instruments drift over time. In electronic
instruments, components that make the measurements right gradually change. That
means the readings made by that meter gradually wander away from their match
with internationally accepted values, so it needs to be periodically checked
and adjusted to make the measurement right again.