Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

[Phys-L] Re: USB and data collection delays



I did the same sort of test with Pasco's data studio software and a
photodiode. I also observed no flash. Ramp up time ~ 30 ms, then
gradual 30ms curve over to a level reading modulated by 60 Hz ripples.
Shut down takes ~ 200 ms as ecpected. This was done with frosted bulb
and a clear showcase bulb - no difference
James Mackey

John SOHL wrote:

I have reprogrammed the system and can now get the full 1.2 kS/s rate.
I've already collected some data and it looks very much like Michael's
data. Again, no flash. I've measured a heat lamp, a regular lamp, an
old
neon lamp with screw base, etc. I've got a bunch of tests this week so
it will likely be next week when I can get back to this. It is fun to
notice that you can easily see the AC on power up as humps on top of
the
ramp up, but on power down that is all gone.

The USB delay is caused by handshaking. The 20 ms is the round trip
time for the computer to poll, the device to answer the handshakes to
be
made and the data transferred. The data transfer rate is fast. The way
I'm doing it now the data is transferred in packets so that the back
and
forth handshaking only happens once in a while. Thus, I can use the
full
speed of the USB. The down side is that I don't get any real time data
display during collection. This is the same thing Vernier does and you
have noticed the in flow of data after the fact.

The system I'm using is made by Measurement Computing. It is called
the
miniLAB 1008 and it costs $109 if I remember right. The main advantage
is that it is more "industry standard" than LabPro and I use it to
teach
LabVIEW to my upper division students. It also has a lot of digital
I/O
that I use to control stepper motors on lasers and spectrometers. It
has
analog out and analog in. It has screw terminals on the top of it
which
makes it easy to use too. While it is slow, for the price it solves
most
of my needs. It comes with some powerful software that is similar to
LabVIEW but you must have Visual Studio .NET installed to use it. When
I
do need a faster system I just use a computer with an internal PCI
slot
card for data acquisition then I can easily get 500 kS/s data rates.
(For a price!)

By the way, the SoftWire software that comes with the miniLAB 1008
sells
for $495 by itself. Thus, getting the miniLAB and the software for $109
is
a pretty good deal. BUT you must have the (expensive) Visual Studio
.NET
already installed for SoftWire to work. I'm going to try it on one of
my
computers eventually, in the meantime, I'm happy enough with LabVIEW
which is also expensive, but I already have that.

John

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
John E. Sohl, Ph.D.
Professor of Physics
Weber State University
2508 University Circle
Ogden, UT 84408-2508

voice: (801) 626-7907, fax: (801) 626-7445
e-mail: jsohl@weber.edu
web: http://physics.weber.edu/sohl/



Bernard Cleyet anngeorg@PACBELL.NET> 11/15/2005 8:07:38 pm >>



Now I know (possibly) why Vernier's LabPro keeps sending data after
collection stops. You don't have a Vernier LabPro or even a ULI,
which
may also collect data rapidly?

Now I'm puzzled, USB is capable of transmitting 1.5 => 480 bps. I'd
think even the slowest rate would accommodate several C Hz collection.
Maybe your resolution is very high?

The LabPro sample rate is 50 k/s w/ 12 bit resolution. It's only
$220;
the driver, Logger Pro, is $150 (includes graphing w/ fitting, and
much
more)


_______________________________________________
Phys-L mailing list
Phys-L@electron.physics.buffalo.edu
https://www.physics.buffalo.edu/mailman/listinfo/phys-l