PSN-L Email List Message

Subject: Re: A/D bits, LP filters
From: barry lotz gbl@.......
Date: Fri, 12 Jan 2001 22:38:11 -0800

Hi Karl
   I look at the 16 bit digitizer as an alternate to a autogain system. I tried
autogain changing during events and the bookkeeping became a problem as did the
slight zero shifts during gain changes. I would like to record both local and
distant signals and seem to use most of the 16 bits . The smallest event p-p I
recorded recently is about 500.  With a use of 10% of this for minimum signal it
would be around 50. I have been wanting to lower my gain a little recently. Looks
like with todays event down south  I may clip again.

Karl Cunningham wrote:

> Hi Sean-Thomas --
> You're right.  I didn't mean accuracy.  But I'm not sure I really meant
> resolution either.  Perhaps "precision" (or distortion level) might have
> been a better choice of words.
> What I was trying to say (and please correct me if I'm wrong) is that it
> isn't necessary for the system to faithfully record the waveform to within
> 15ppm (16 bits) for a full-scale signal.  For very small signals you want
> to get as many bits of good data as possible.  But if the signal is large,
> perhaps allowing an imprecision (in other words distortion, including
> aliases) of something like 8 bits (0.4% of the peak-to-peak signal at the
> time) may be good enough.  Of course, it depends completely on what the
> data is to be used for.
> I was suggesting that the compromise of allowing unintentionally aliased
> out-of-band signals may be ok as long as they are below some fraction of
> the overall signal level at that time, given the resultant benefit of
> decreased circuit complexity.
> Karl


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Larry Cochrane <cochrane@..............>