[SI-LIST] Re: ppm(parts per million)-Crystal OSC
- From: Rick Collins <gnuarm.2006@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 02 Jan 2012 13:30:00 -0500
Most of what you say is true, there is a
difference between accuracy and precision. These
are theoretical properties. Tolerance is a
practical quantity and is intended to include all
variation from the specified value to the actual
value or at least a set of specific
deviations. I don't believe that tolerance is
the same as precision really. Oddly enough a
google search did not easily turn up a good definition.
In the context of crystal or oscillator specs, I
believe tolerance is more similar to accuracy,
intended to specify the allowed variation of
initial frequency without considering
environmental factors such as temperature or
other effects such as aging. Typically a crystal
maker specifies a tolerance as well as a
temperature dependency and possibly an aging rate.
If you really want to know how tolerance is
defined for a given part, ask the
manufacturer. I have found them happy to answer
nearly any question about their datasheets or testing methods.
Rick
At 12:44 PM 1/2/2012, Daniel deAraujo wrote:
>Bala:
> Tolerance (as precision) is indicative of the variability. From
>sample to sample, how much does a particular value change? Accuracy is how
>close you are to the intended target or true value. You can have low
>tolerance/high precision, but be off target, as well as having accuracy
>without tight tolerance. Ideally, you want low tolerance and high
>accuracy, but this may come at a higher price depending on the requirements.
>
>
>Sincerely,
>
>* Daniel N. de Araujo
>*Director of Applications, *Nimbic*
>Electromagnetic Integrity 3D full-wave solutions for SI, PI & EMI
>www.nimbic.com
>
>
>
>On Mon, Jan 2, 2012 at 7:41 AM, bala <balaseven@xxxxxxxxx> wrote:
>
> > Are tolerance and accuracy same?
> > bala
> >
> > On Thu, Dec 15, 2011 at 2:15 PM, Jayaprabakaran <
> > jayaprabakaran.k@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > > Hi Hilal and Vikas,
> > >
> > >
> > > Thanks for the clarification.
> > >
> > >
> > >
> > > Regards,
> > >
> > > Jp
> > >
> > >
> > >
> > > _____
> > >
> > > From: vikas dhanda [mailto:vikasdhanda7@xxxxxxxxx]
> > > Sent: Thursday, December 15, 2011 1:14 PM
> > > To: Jayaprabakaran
> > > Cc: si-list@xxxxxxxxxxxxx
> > > Subject: Re: [SI-LIST] Re: ppm(parts per million)-Crystal OSC
> > >
> > >
> > >
> > > Frequency tolerance (in ppm)=>The Frequency Tolerance of a crystal or
> > > oscillator is defined as the initial deviation of the crystal or
> > oscillator
> > > frequency as compared to the absolute at 25°C like it designed for 25Mhz
> > > but
> > > measured is 24.999946Mhz So this is the frequency tolerance.
> > >
> > >
> > >
> > > Where the
> > >
> > >
> > > Frequency stability is the frequency deviation compared to the measured
> > > frequency at 25°C over the defined operating temperature and voltage
> > > range.Here we consider 24.999946Mhz as actual frequency (as Measured) and
> > > calculate PPM with this Frequency but don't consider 25Mhzfor
> > calculation.
> > >
> > >
> > >
> > >
> > >
> > > Regards,
> > >
> > > Vikas Dhanda
> > >
> > > On Thu, Dec 15, 2011 at 10:25 AM, Jayaprabakaran
> > > <jayaprabakaran.k@xxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > >
> > > Most of the crystals have two ppm values.
> > > Frequency tolerance (in ppm) and Frequency stability (in ppm).
> > > What are the difference b/w two parameters?
> > >
> > > Regards,
> > > Jayaprabakaran
> > >
> > >
> > > -----Original Message-----
> > > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > > On
> > >
> > > Behalf Of Mike Poorman (Cascade Engineering Svcs Inc)
> > > Sent: Wednesday, December 14, 2011 11:22 PM
> > > To: 'si-list@xxxxxxxxxxxxx'
> > > Subject: [SI-LIST] Re: ppm(parts per million)-Crystal OSC
> > >
> > > Think of PPM as a tolerance on the frequency. The smaller the PPM number
> > > the more accurate and stable the crystal frequency will be.
> > >
> > > Mike Poorman
> > > EMC Technician
> > > Cascade Engineering Services, Inc.,
> > > Email: v-mipoor@xxxxxxxxxxxxx
> > >
> > > This email message may contain confidential and proprietary information.
> > > Any unauthorized use is prohibited. If you are not the intended
> > recipient,
> > > please contact the sender by reply email and destroy all copies of the
> > > original message.
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > > On
> > > Behalf Of bala
> > > Sent: Wednesday, December 14, 2011 2:17 AM
> > > To: si-list@xxxxxxxxxxxxx
> > > Subject: [SI-LIST] ppm(parts per million)-Crystal OSC
> > >
> > > Hi all,
> > > I have a little confusion on PPM vs frequency of Crystal Oscillators.How
> > > important is the term 'ppm' than frequency.Why all the datasheets have
> > both
> > > units,ppm and Hz.Please clarify,Also how much important is the value of
> > ppm
> > > on the Signal integrity side,if any.Thanks for your time.
> > >
> > > --
> > > bala
> > >
> > >
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> > --
> > bala
> >
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