Re: How to terminate the function that runs every n seconds

From	Grant Edwards <invalid@invalid.invalid>
Newsgroups	comp.lang.python
Subject	Re: How to terminate the function that runs every n seconds
Date	2015-01-14 18:05 +0000
Organization	PANIX Public Access Internet and UNIX, NYC
Message-ID	<m96b61$oek$1@reader1.panix.com> (permalink)
References	(1 earlier) <CACT3xuUr-07yW-FjiKBjPbsbn5j7r1vUfu1E0A6Myz=7sYpnzA@mail.gmail.com> <54B69A5B.5000801@davea.name> <mailman.17726.1421254466.18130.python-list@python.org> <m969fs$cic$1@reader1.panix.com> <mailman.17732.1421258062.18130.python-list@python.org>

Show all headers | View raw

On 2015-01-14, Mark Lawrence <breamoreboy@yahoo.co.uk> wrote:
> On 14/01/2015 17:37, Grant Edwards wrote:
>> On 2015-01-14, Mark Lawrence <breamoreboy@yahoo.co.uk> wrote:
>>
>>> Reminds me of working on Telematics S200/300/4000/5000 telecomms kit in
>>> the early 90s where the timers were mains based, so a one hour timer
>>> would go off at about one hour, 30 seconds.
>>
>> I don't understand.  Power line frequencies are _very_ accurate and
>> have been relied upon for timekeeping since the 1930s.  We're talking
>> a few hundred PPM over a 24 hour period.  A 30 second error over a one
>> hour period seems _really_ high.
>
> http://www2.nationalgrid.com/uk/services/balancing-services/frequency-response/ 
> "National Grid has a licence obligation to control frequency within the 
> limits specified in the 'Electricity Supply Regulations', i.e. ±1% of 
> nominal system frequency (50.00Hz) save in abnormal or exceptional 
> circumstances.".  I wouldn't describe ±1% as very accurate and certainly 
> not within a few hundred ppm.

Sorry, I should have guessed from the use of the word "mains" that you
were in the UK -- which seems to have much laxer power-line frequency
regulation than the US.

> I'm assuming that this kind of limitation applies around the world,
> so could you be getting confused with some other more accurate
> frequency control?

Power line frequency control in the US is much tighter than the UK.
According to real-world data I've seen, powerline-based timings are
typically accurate to a few seconds per month.  In the US, they
implement freqency corrections every hour to keep long term,
cumulative time errors under a certain limit (the limit ranges from 2
to 10 seconds depending on region).

-- 
Grant Edwards               grant.b.edwards        Yow! I love ROCK 'N ROLL!
                                  at               I memorized the all WORDS
                              gmail.com            to "WIPE-OUT" in 1965!!

Back to comp.lang.python | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Re: How to terminate the function that runs every n seconds Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-01-14 16:54 +0000
  Re: How to terminate the function that runs every n seconds Grant Edwards <invalid@invalid.invalid> - 2015-01-14 17:37 +0000
    Re: How to terminate the function that runs every n seconds Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-01-14 17:54 +0000
      Re: How to terminate the function that runs every n seconds Grant Edwards <invalid@invalid.invalid> - 2015-01-14 18:05 +0000

csiph-web