=20
I saw this A/D on Ebay and decided to try it . I bought the two channel =
version for $99. =20
I tested it using the included software with the inputs terminated in =
100 ohms. The result was EXTREMELY POOR !!!!=20
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 .=20
This is not too surprising based on the specs for the low cost =
delta-sigma A/D chips.=20
The software makes and displays a record from the start time to the end =
time.=20
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.=20
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.=20
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. =20
Save your money on this one.
Dave Nelson=20
Rolling Hills Estates , California =20
Do any of you have any experience with these ACD devices. They appear =
to compete with DataQ products.
=20
http://www.futekinst.com/futek/dataacquisitionsystem.asp
=20
I saw this A/D on Ebay and decided to =
try it . I=20
bought the two channel version for $99.
I tested it using the included software =
with the=20
inputs terminated in 100 ohms. The result was EXTREMELY POOR=20
!!!!
The noise level is ~2000 counts =
peak to peak=20
apparently independent of the sample rate. This results in an effective=20
resolution of closer to 12 bits not 24 on a p-p basis . =
This is not too surprising based on the =
specs for=20
the low cost delta-sigma A/D chips.
The software makes and displays a =
record from=20
the start time to the end time.
The time resolution of the real time =
display gets=20
worse as the record length gets longer. It is not a scope type display =
with a=20
variable time interval.
So far I have come to the =
conclusion this=20
thing is useless with its included software. There are .dll =
files for=20
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=20
sample rate is varied leads me to the initial conclusion that the A/D is =
running=20
at a fixed high sample rate and the lower effective sample rates are=20
derived by pure decimation. =
I need to take a closer look at it but =
so far I am=20
totally unimpressed and don't recommend this device for any useful=20
purpose.
24 bit A/D's in general do not perform =
as well as=20
one would expect or hope . Read the effective resolution specs very =
carefully=20
and note that they usually refer to RMS noise whereas the=20
noise we want to use for seismic records is most likely peak to=20
peak. The difference is 3 to 4 bits.
We are not in the audio business =
where RMS=20
noise may be more appropriate. Frequently the effective =
resolution is=20
not much better than 16 bits at 200 sps.
Larry clearly understand the importance =
of the=20
noise and goes to great lengths to reduce it in his A/D =
boards. =20
Sometimes the very expensive 24 bit A/Ds are not nearly as good as =
the=20
manufacturers lead one to believe.
Save your money on =
this=20
one.
Dave Nelson
Rolling Hills Estates , California=20
Do any of you have any experience with these ACD devices. =
They appear=20
to compete with DataQ products.
http://=
www.futekinst.com/futek/dataacquisitionsystem.asp
=
These=20
device appear to compete with DataQ with 16 or 24 bit offering.=20