Boiling point of water in Fahrenheit??? Not a SI unit.
Using a "calibrated" thermometer to check another??? Who "Calibrates"
the "calibrated" standard, and what are it's uncertainties.
Speed of light constant??? In a vacuum perhaps, rarely in any other medium.
In truth, all that is a performance check.? A "Calibration" is when an
instrument is adjusted to read/indicate as close to what is assumed to
be a standard, and then results are taken.? (I used to do just that,
some decades ago, at a major test equipment makers UK service center.)
Not as common (or needed as frequently now) as it used to be, as the
stability of technology has improved over the years, except were
American makers still insist on using carbon composition resistors in
not uncritical parts of a circuit!? (Sadly, one I work for, and others
we represent.)?? (5% marked parts, are usually over 10 or 15% off the
marked value!)
We've had instruments "Formally Calibrated" by a certain UK cal' house,
that when we checked on their return, the "Calibration" figures are out
of spec' for that instrument!?? How can that be??? (Resolved now, as
they used a moving coil meter display "Standard", not even a mirrored
scale, to "Calibrate" a digital indicating, to at least two significant
digits, instrument...)
We've also had brand new equipment, that come with a "Calibration
Certificate".? But when we check (with multiple different
instruments/devices) and find that the "new" equipment is out of
specification as made, sometimes by quite some way.
We query it with the manufacturer, they issue an updated specification
and certificate that then encompasses the original discrepancy.? (Not
only Far East makers, but one or two US makers too!)
RF Connector "Gauging" in particular is often missed as a cal' check on
items such as attenuators, couplers and cables.?? As well as
"calibrating" directional couplers, using instruments that don't have
sufficient dynamic range to determine directivity accurately.? (From the
list of used equipment, if that is reported.)
One cal' house even "lost" an interconnecting lead.? They said they had
never received it from us, but it's reference number etc, were included
on the resulting cal' cert...?? They still insisted they never had it.?
We lost the will to live, and bought another lead ourselves, as we
needed a working instrument.
I'm sure there are a lot of "Good" Calibration Houses out there, but the
majority of manufactures own, and plenty of third party houses are not
worth the cost of the paperwork.? Especially where equipment is
manufactured "offshore", and they just shift boxes without unpacking,
running up and checking the product actually works to specification
before sending to the customer.
Frankly.? If you "Need" to accurately measure something.? Do it with at
least two different methods, or instruments of different types.?
Especially where RF power is concerned, and significant harmonics are
present!
And first verify the instruments against again at least two known good
references.
Regards to All.
Dave (G8KBV)? Recalibrating the house, by moving all the furniture
around today.? By order of "Management"...
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