[SI-LIST] Re: Question of taking measurement. Thanks.
- From: Ihsan Erdin <erdinih@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 9 Dec 2005 20:13:26 -0500
Peng,
If we're talking about (digital) sampling scopes we have to make a
distinction between the bandwidth and the sampling rate. The bandwidth of
the scope should be high enough to account for the frequency contents of the
signal rise time. In order to meet the Nyquist criterion, the sampling rate
should be at least twice as much as the measurement bandwidth. However, to
minimize uncertainty, a sampling rate of about 8 to 10 times of the
measurement bandwidth is usually recommended.
Regards.
Ihsan
On 12/9/05, Bill Wurst <billw@xxxxxxxxxxx> wrote:
>
> Hi Peng,
>
> The bandwidth requirement of the test equipment will depend on the
> harmonic content of the signal you are observing and the level of
> accuracy you require. For example, if you are measuring a sinusoid and
> don't mind the observed amplitude being low by as much as 10-20%, then
> BW=2*f should be fine. However, if the signal of interest is a
> square-wave, then your oscilloscope should have 5-10 times the bandwidth
> of the fundamental to observe a reasonable replica of the actual
> waveshape. You must also keep in mind that when measuring fast edges,
> the observed transition time will be increased by the bandwidth of the
> instrument, and that transition times of cascaded systems add roughly in
> root-sum-of-squares fashion. Your measurement technique (i.e., probe
> ground inductance, etc.) will also influence high-speed measurements.
> For more information on this subject, I would suggest the websites of
> Agilent, LeCroy, and Tektronix.
>
> Regards,
> -Bill
>
>
> /************************************
> / billw@xxxxxxxxxxx /
> / /
> / Advanced Electronic Concepts, LLC /
> / www.aec-lab.com /
> ************************************
> ========================================================
> Peng Ye wrote:
> > Hi everyone,
> >
> > To get accurate results, the bandwidth of the oscilloscope must be
> 2X+ of the signal. (Please correct me if I'm wrong. Thanks.) So if I know
> that the bandwidth of my scope is not enough compared to the signal that I
> want to measure, is that any way I can still get accurate results? (This may
> be well discussed, but I have no idea about this as a new scope user. I very
> appreciate any of your answer.)
> >
> > Thank you very much.
> >
> > Yours,
> > Peng
> >
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