PSN-L Email List Message
Subject: Re: 24bits A/D converters & seismology
From: Hammonds hammond@...........
Date: Thu, 04 Jul 2002 13:52:15 -0800
This is from the ORFEUS
"The digitizer is a critical part in a VBB seismograph. It must however
cover a dynamic range of at least 140 dB, and it must have
an excellent linearity and resolution because signals of greatly different
amplitude may simultaneously be present in different
parts of the VBB seismic band."
So, the desire to have high dynamic range recording from broadband
seismometers is in part why 24-bit digitizers are used.
At 01:43 PM 7/4/2002, you wrote:
>Is it not the case that most commercial seismometers these days are
>wideband instruments? If so, they may need 24 bits to handle the
>much larger dynamic range of these instruments. Its possible that
>20 bits might be enough, but vendors may have decided to go for the
>extra 4 bits rather than restrict the range. Considering the price
>of a commercial instrument, the extra 4 bits probably does not add
>to the cost of construction sufficiently to warrant changing the
>price. Its also possible that 24 bits (3 bytes) is preferred,
>because it slightly simplifies the data processing software.
>----- Original Message -----
>Date: Thursday, July 4, 2002 12:04 pm
>Subject: Re: 24bits A/D converters & seismology
> > Hello Jim,
> > thank you for your answer!
> > Of course I understand that amateur systems do not need a 24bit A/D
> > converter : )
> > But I am wondering what is the reason why commercial seismometers
> > have a
> > 24bit A/D convertor.
> > How do you explain the need for such a hight sensitivity? (120
> > nano-g this
> > is so small!)
> > Don't you think that the seismic noise (assuming the eletronic
> > noise is
> > reduced to minimum) is much bigger than hundrerds of nano-g ?
> > Do you think that commercial seismometers really use the full
> > 24bit output
> > of there convertors? won't it be much enough to use 20bits (2
> > micro-g
> > resolution) ?
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