if you want a usb daq, then have a look at
http://sine.ni.com/nips/cds/view/p/lang/en/nid/201987 I haven't used
usb versions but I know their products are very good. I use a pci
version for my system. Some software comes with the device but I don't
know if it would do all that is needed for a station.
You also get them on ebay.
cheers
Ian
On 04/01/2011 23:53, Dave Nelson wrote:
>
> I saw this A/D on Ebay and decided to try it . I bought the two
> channel version for $99.
> I tested it using the included software with the inputs terminated in
> 100 ohms. The result was EXTREMELY POOR !!!!
> The noise level is ~2000 counts peak to peak apparently independent
> of the sample rate. This results in an effective resolution of closer
> to 12 bits not 24 on a p-p basis .
> This is not too surprising based on the specs for the low cost
> delta-sigma A/D chips.
> The software makes and displays a record from the start time to the
> end time.
> The time resolution of the real time display gets worse as the record
> length gets longer. It is not a scope type display with a variable
> time interval.
> So far I have come to the conclusion this thing is useless with its
> included software. There are .dll files for windows if one could write
> new or adapt existing software for display/analysis but that may not
> improve the noise.
> The apparent independence of the noise as the sample rate is varied
> leads me to the initial conclusion that the A/D is running at a fixed
> high sample rate and the lower effective sample rates are derived by
> pure decimation.
> I need to take a closer look at it but so far I am totally unimpressed
> and don't recommend this device for any useful purpose.
> 24 bit A/D's in general do not perform as well as one would expect or
> hope . Read the effective resolution specs very carefully and note
> that they usually refer to RMS noise whereas the noise we want to
> use for seismic records is most likely peak to peak. The difference is
> 3 to 4 bits.
> We are not in the audio business where RMS noise may be more
> appropriate. Frequently the effective resolution is not much better
> than 16 bits at 200 sps.
> Larry clearly understand the importance of the noise and goes to great
> lengths to reduce it in his A/D boards. Sometimes the very expensive
> 24 bit A/Ds are not nearly as good as the manufacturers lead one to
> believe.
> Save your money on this one.
> Dave Nelson
> Rolling Hills Estates , California
> Do any of you have any experience with these ACD devices. They appear
> to compete with DataQ products.
>
> http://www.futekinst.com/futek/dataacquisitionsystem.asp
>
> These device appear to compete with DataQ with 16 or 24 bit offering.
You also get them on ebay.
cheers
Ian
On 04/01/2011 23:53, Dave Nelson wrote:
I saw this A/D on Ebay and
decided to try it . I bought the two channel version for $99.
I tested it using the included
software with the inputs terminated in 100 ohms. The result
was EXTREMELY POOR !!!!
The noise level is ~2000 counts
peak to peak apparently independent of the sample rate. This
results in an effective resolution of closer to 12 bits not
24 on a p-p basis .
This is not too surprising based
on the specs for the low cost delta-sigma A/D chips.
The software makes and displays
a record from the start time to the end time.
The time resolution of the real
time display gets worse as the record length gets longer. It
is not a scope type display with a variable time interval.
So far I have come to the
conclusion this thing is useless with its included software.
There are .dll files for windows if one could write new or
adapt existing software for display/analysis but that may not
improve the noise.
The apparent independence of the
noise as the sample rate is varied leads me to the initial
conclusion that the A/D is running at a fixed high sample rate
and the lower effective sample rates are derived by pure decimation.
I need to take a closer look at
it but so far I am totally unimpressed and don't recommend
this device for any useful purpose.
24 bit A/D's in general do not
perform as well as one would expect or hope . Read the
effective resolution specs very carefully and note that they
usually refer to RMS noise whereas the noise we want to use
for seismic records is most likely peak to peak. The
difference is 3 to 4 bits.
We are not in the audio business
where RMS noise may be more appropriate. Frequently the
effective resolution is not much better than 16 bits at 200
sps.
Larry clearly understand the
importance of the noise and goes to great lengths to reduce it
in his A/D boards. Sometimes the very expensive 24 bit A/Ds
are not nearly as good as the manufacturers lead one to
believe.
Save your money on this one.
Dave Nelson
Rolling Hills Estates ,
California
Do any of you have any experience with these ACD devices.
They appear to compete with DataQ products.
http://www.futekinst.com/futek/dataacquisitionsystem.asp
These device appear to compete with DataQ with 16 or 24 bit
offering.