[GTALUG] mysterious restarts

[Michael Galea]

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