Check frequency
in [Basics]
|
From: ClueLess on 17 Dec 2009 21:01 On Wed, 16 Dec 2009 09:25:28 -0600, John Fields <jfields(a)austininstruments.com> wrote: >For this application an oscilloscope will be useless and you should use >a frequency counter. Thank you very much got your very detailed suggestions, I will look for a frequency counter and try as you said. -- Thanks again ClueLess
From: Phil Allison on 17 Dec 2009 21:31 "John Fields" "Phil Allison" >> >>>>** To get the frequency exact, you need resolution better than 1 Hz >>> >>> I don't think so. >> >> ** You don't think straight at all. >> >> Never have. > > Just because you don't recognize it as straight thinking doesn't mean it > isn't. ** Fraid it is just more of your crazed, autistic crapology. > For example, if you think that the '8' in 32768 Hz represents 1 Hz, as > you seem to indicate, I suggest you consider that it represents 1 part > in 32768 Hz, which is ~ 30.5�s, not 1s/1Hz. ** Fraid it is just more of your crazed, autistic crapology. ....... Phil
From: whit3rd on 18 Dec 2009 00:31 On Dec 17, 6:01 pm, ClueLess <cluel...(a)wilderness.org.invalid> wrote: > On Wed, 16 Dec 2009 09:25:28 -0600, John Fields > > <jfie...(a)austininstruments.com> wrote: > >For this application an oscilloscope will be useless and you should use > >a frequency counter. > > Thank you very much got your very detailed suggestions, I will look > for a frequency counter and try as you said. Er... no, that's not right. If you have a suitable reference frequency source, you can watch the pretty Lissajous figure on an X/Y oscilloscope (no dual channel, no counter) and if it goes through a cycle in 100 seconds, with 0.1 second stopwatch accuracy, you've just made a frequency measurement with .001 Hz accuracy. For your 32 kHz crystal, that's a second per year kind of accuracy. A frequency counter is a convenient and quick solution, but it is NOT required nor is it superior in accuracy.
From: Phil Allison on 18 Dec 2009 01:39 "whit3rd" ClueLess John Fields > >For this application an oscilloscope will be useless and you > > should use a frequency counter. > > Thank you very much got your very detailed suggestions, I will > look for a frequency counter and try as you said. Er... no, that's not right. If you have a suitable reference frequency source, you can watch the pretty Lissajous figure on an X/Y oscilloscope (no dual channel, no counter) and if it goes through a cycle in 100 seconds, with 0.1 second stopwatch accuracy, you've just made a frequency measurement with .001 Hz accuracy. For your 32 kHz crystal, that's a second per year kind of accuracy. A frequency counter is a convenient and quick solution, but it is NOT required nor is it superior in accuracy. ** Ask JF where the OP can get an affordable counter that reads a frequency in Hz to seven decimal places - as in his " 32768.XXXXXXX Hz ". His magic 10 turn crystal PU loop need to be patented too. ....... Phil
From: John Fields on 19 Dec 2009 15:29
On Thu, 17 Dec 2009 21:31:35 -0800 (PST), whit3rd <whit3rd(a)gmail.com> wrote: >On Dec 17, 6:01�pm, ClueLess <cluel...(a)wilderness.org.invalid> wrote: >> On Wed, 16 Dec 2009 09:25:28 -0600, John Fields >> >> <jfie...(a)austininstruments.com> wrote: >> >For this application an oscilloscope will be useless and you should use >> >a frequency counter. >> >> Thank you very much got your very detailed suggestions, I will look >> for a frequency counter and try as you said. > >Er... no, that's not right. If you have a suitable reference >frequency source, --- Ah, so now it's a "suitable reference source:? Just what might that be? --- >you can watch the pretty Lissajous figure >on an X/Y oscilloscope (no dual channel, no counter) and if >it goes through a cycle in 100 seconds, with 0.1 second >stopwatch accuracy, you've just made a frequency >measurement with .001 Hz accuracy. --- With the crystal running at about 32768 Hz, how do you propose to make one cycle last for 100 seconds? Furthermore, Lissajous figures are generated by signals applied to the X and Y axes of the scope, so how do you propose to see anything meaningful with, say, Y running at 32768 Hz and X running at 100 seconds? --- > For your >32 kHz crystal, that's a second per year kind of accuracy. --- If, as you've stated, you have a 100s timebase which is accurate to +/- 0.1s, then it'll be accurate to one part in 1000, which is +/- 1000ppm. Then, since there are 60 * 60 * 24 * 365.25 = 31 557 600 seconds in a year it'll be accurate - not to "a second per year kind of accuracy" - but to 3156 seconds = 52.6 minutes per year kind of accuracy. --- >A frequency counter is a convenient and quick solution, but >it is NOT required nor is it superior in accuracy. --- Since most frequency counters have time-base oscillators with accuracies much, much, better than 1000ppm, I'd say their accuracies were vastly superior to what could be realized using the hare-brained scheme you propose. Wouldn't you agree? JF |