On 06/22/16 16:35, Alvin Starr via talk wrote:
On 06/22/2016 01:25 PM, Jamon Camisso via talk wrote:
On 2016-06-22 17:46, D. Hugh Redelmeier via talk wrote:
Remember, he truncated the values (grep does not round).
My best guess: the average of the readings would be from a
distribution centred on 59.996435 (0.005 larger than Lennart
calculated). It could be as low as 59.991435 or as high as 60.991434,
assuming six digits of precision in the fraction. I know nothing
about accuracy of the device.
Summary: the 60Hz hypothesis is not excluded by the evidence. Far
from it.
P.S. "grep -c" eliminates the need for "wc -l".
and sort/uniq eliminate even more:
cat /tmp/MGC|sort -n |uniq -c
16 FREQ value 59.95
99 FREQ value 59.96
282 FREQ value 59.97
464 FREQ value 59.98
459 FREQ value 59.99
385 FREQ value 60.00
302 FREQ value 60.01
144 FREQ value 60.02
68 FREQ value 60.03
3 FREQ value 60.04
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Another question is how accurate is the device doing the measurements.
If this is a UPS then the monitoring is not designed for accurate
frequency measurements.
Get out your 6+ digit frequency counter and then run the tests.
No, the device is not a UPS. It is a PLC that measures voltages,
currents, real and reactive power of a 3-phase service. It provides me
the results as IEEE754 32-bit floating point numbers. It's me that
truncates to 2 digits.
You know I'm sorry I ever implied that the grid wasn't long term
accurate at 60 Hz! What I should have said was that in the short term
the grid could be quite off 60 Hz but over the longer term it could
average out.
If I really needed to know the answer to the question of "how much out",
I would get ask the PLC to just count cycles and send me the count with
a timestamp. That would tell.
--
Michael Galea
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