Petr and all,
Those digital instruments that show 2, 3, or 4 decimal places have given
us a false sense of accuracy.
For instance an instrument that is accurate to 5% and has a 4 digit
display can show us (when measuring a 5 volt source) anywhere between
4.750 volts and 5.250 volts and still be within the 5% accuracy window
for the instrument.
Review the specs and calibration for whatever meter you are using and do
not expect those extra digits to be correct - in other words round the
numbers displayed.
Many wattmeters are only accurate to 20% of the reading - so if one
wattmeter at 100 watts shows 120 watts and another shows 80 watts, the
actual power could be 100 watts. Take that into consideration.
The Telepost LP-100 when calibrated to NIST standards is accurate to 5%
(it can be lower, but Larry will not guarantee it). So any power it
displays between 95 and 105 watts can actually be 100 watts.
In other words, look at the specified accuracy of whatever meter you are
using and take that into consideration. Those extra digits on your
meter may be meaningless.
73,
Don W3FPR
On 11/30/2018 9:29 AM, Petr, OK1RP/M0SIS wrote:
Hi Wes,
excellent!
Many thanks for this post which is nicely explaining what is going on about
the measurement in K3s.
In fact until now no one talked about the calibrations, uncertainties,
errors, accuracy, reading errors, uncertainties A, B and combined
uncertainties etc. In that case there is several error sources and factors
which need to be calculated in order to get some more precise values ...and
in all cases the uncertainties must be calculated together with measured
value if we would like to talk about scientific or sophisticated
measurement.
Thanks for nice explanation Wes to all.
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