PSN-L Email List Message
Subject: Re: Modified sound card and datalogging and geophones
From: Gordon Couger gcouger@..........
Date: Thu, 21 Jul 2005 01:03:18 -0500
> In a message dated 20/07/2005, gcouger@.......... writes:
> Out of sequence and possible not on subject but it has
> on timing that are important. I must have come in the
> don't understand your set up. I thought you were
recording data to
> disk with a computer sound card.
> I am working on a seismometer that records several
> one time in the 0-50 HZ range on the two channels of a
> for imaging shallow aquifers looking for larger gravel to
> better water well in a shallow aquifer along Red River
> between Oklahoma and Texas so I can afford to put in
> I have probably imposed my project on yours without
> Hi Gordon,
> We were discussing sound cards and I was rejecting this as
> impractical for seismic purposes. The data files are massive
> haven't found a way of using the 24 bit soundcard ADC for 20
> Chuck a bit of cash at it and get rid of the your
> sells a fairly good 8 channel serial board, which you can use
with a GPS
> If you want to play, fine. If you want to work, get rid
> that you do not need to have.
> Just what rate of water rise do you get along the Red
> for marine waves, 20 sps is adequate and most geological
systems will go
> to 100sps, some even more.
> >> A GPS will give you the best time stamp you could ask
> even have a 100 kHz clock as well a 1 second pulse that are
> GPS clocks. They can be used to phase lock frequency sources
> super accurate osillators.
> I am NOT asking for the best system, just one that
> inexpensive, low power and ADEQUATE for my purposes.
> I use VLF timing signals. You can get relatively inexpensive
> receiver boards with a ferrite aerial: or gut a radio clock.
> about 10 mS + the transit time. The only folks who need it
> monitor volcanoes of do reflection seismometry. I have been
> this road. I would be great if Larry would fit the software
> WWVB directly, but he seems concentrate on GPS. GPS is power
> needs a clear line of sight to satellites; 60 KHz VLF radio
is low power
> and can be used most anywere. I can use it where I can't get
> even underground. Just keep it away from striplights, radio
> transmitters, TVs and computer monitors. I have used it
> radio and TV transmitters - find a nice hole and bury it to
> It is no accident that submarine communications use the VLF
> If you are not interested in 1 to 20 Hz signals sound
> pretty good tools. If you are really serious about low
> and accurate timing Windows poses a lot of problems.
> 0 to 10 Hz is my range of interest. I want about +/-0.1 sec
> accuracy, 24 hrs / day. This is why I use an ADC which has
it's own on
> board timing and correction. The data goes to the hard disk
with a time
> stamp regardless of the rubbish timing on the operating system.
> First Windows is an event driven operating system and
there is no
> assurance when a program will run. The sound card gets
> but you have to put a chirp on the signal to synchronize
> time you can depend on the computer clock or the RS232 port.
> Can you say that again please? I don't quite understand.
> Having worked with embedded systems for the last 20 years
> choose a real time computer. There are real time versions
> but I think that's over kill for dataloging geophones.
> You have the real and the software clocks on computer
> used to be able to get 4.194 MHz AT crystal clocks on
> could be made moderately reliable. All the boards that I have
> recently use 32 KHz crystals which appear to be rejects from
> manufacturers. A random error of 20 sec to 2 min a day is
what I call
> utter ****. If you had a quartz watch which was that bad, you
> it back to the shop and demand your money back.
> A GPS for a time base, a good a/d converter and fast
> would be the way I would do it. I am working with a very
> 60 MHz with 4 10 bit A/D channels
> Does 10 bits give you enough resolution, taking into
> noise? The Dataq $25 starter ADCs give you 4 Channels at 240
sps total -
> 60 sps / channel.
> I can't figure out at the moment why you would need a high
> monitoring rate for looking at water levels?
> Chris Chapman
I am not looking for water levels I putting out sensors and
making a shock moving over and making another shock ...... and
another shock and resetting the sensors and doing it over again
to do a seismic study of the aquifer of the water bearing sand
and 30 feet down. I need a post process GPS signal to know where
I am I might as well use the time spruce on it.
Almost everything I work with has a GPS. I did the first vehicle
units for www.ipsolutionsinc.com and all the software for spryer
I agree they are power hogs and take a lot of resources for time
for seismic senors that VLF will do just as well as GPS. I have
seen jitter on VLF from WWV in a really bad magnetic storm but
not as often as I have lost lock with the GPS.
If you want to time sync a signal on a sound card you can depend
on windows for time. It is too uncertain when the windows
routine will time stamp it. Windows can't be made work in real time.
If you want to record 0 to 20 Hz signals on a sound card a mixer
and local oscillator at 500 Hz will move the 0 to 20 Hz to 500
to 520 and the inverse of it to 480 to 500. You can use DSP to
get the signal back from either one.
Ten bits is enough for most situations in vehicles any more is
lost in the noise of the vehicle. In the case of seismometer in
an open field a more sensitive A/D could be used.
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