Analog Input Problems

[bscherer@vision.eri.harvard.edu]

I'm using one of the LabView examples, the simple spectrum analyzer,
without any modifications. When I first run the program, I get perfect
resuts. However, when I run the VI again, there is no signal. It seems
that the analog input is no longer working. If I reboot the computer,
it again works one time.

I checked my signal with a scope, and it is still there. I've tried
using a different analog input pin in case the one I was using was bad,
but that didn't help. I've also tried running a very basic analog input
program with similar results. (Working once only.)

Has anyone else had similar problems, or have any suggestions?

Thanks,

Beth


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[bgscherer@my-deja.com]

Upon further investigation, I found that the DC offset of the input (a
low frequency triangle wave) is actually slowly ramping up to 10 Volts
at which point it flattens out. Hence, it seems to work only once
because by the time I run it again, the signal has flattened out at 10V.

I still do not understand why the analog input is adding some ramping
value to my input.

Any help would be appreciated.

Beth


In article <8hrcgd$aks$1@nnrp1.deja.com>,
bscherer@vision.eri.harvard.edu wrote:
> I'm using one of the LabView examples, the simple spectrum analyzer,
> without any modifications. When I first run the program, I get
perfect
> resuts. However, when I run the VI again, there is no signal. It
seems
> that the analog input is no longer working. If I
reboot the computer,
> it again works one time.
>
> I checked my signal with a scope, and it is still there. I've tried
> using a different analog input pin in case the one I was using was
bad,
> but that didn't help. I've also tried running a very basic analog
input
> program with similar results. (Working once only.)
>
> Has anyone else had similar problems, or have any suggestions?
>
> Thanks,
>
> Beth
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
>


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Before you buy.

[Tariah]

bgscherer@my-deja.com wrote:
>Upon further investigation, I found that the DC offset of the input (a>low
frequency triangle wave) is actually slowly ramping up to 10 Volts>at which
point it flattens out. Hence, it seems to work only once>because by the
time I run it again, the signal has flattened out at 10V.>>I still do not
understand why the analog input is adding some ramping>value to my input.>>Any
help would be appreciated.>>Beth>>>In article <8hrcgd$aks$1@nnrp1.deja.com>,>
bscherer@vision.eri.harvard.edu wrote:>> I'm using one of the LabView examples,
the simple spectrum analyzer,>> without any modifications. When I first
run the program, I get>perfect>> resuts. However, when I run the VI again,
there is no signal. It>seems>> that the analog input is no
longer working.
If I reboot the computer,>> it again works one time.>>>> I checked my signal
with a scope, and it is still there. I've tried>> using a different analog
input pin in case the one I was using was>bad,>> but that didn't help. I've
also tried running a very basic analog>input>> program with similar results.
(Working once only.)>>>> Has anyone else had similar problems, or have any
suggestions?>>>> Thanks,>>>> Beth>>>> Sent via Deja.com http://www.deja.com/>>
Before you buy.>>>>>Sent via Deja.com http://www.deja.com/>Before you buy.


You might want to check your grounds.

[Michel Farhi]

Hi,

I am not sure to understand exactly what's the problem, but a ramping signal
could come come from the way you do the acquisition (Diff mode). Are you in
Diff mode or in RSE? Look at the DAQ Basic Manual about about to connect
signals to your board, depending on their types. I hope this helps.

-Michel

[markwysong@my-deja.com]

In article <8hrlaj$hpu$1@nnrp1.deja.com>,
bgscherer@my-deja.com wrote:
> Upon further investigation, I found that the DC offset of the input (a
> low frequency triangle wave) is actually slowly ramping up to 10 Volts
> at which point it flattens out. Hence, it seems to work only once
> because by the time I run it again, the signal has flattened out at 10V.
>
> I still do not understand why the analog input is adding some ramping
> value to my input.
>
> Any help would be appreciated.
>
> Beth
>
> In article <8hrcgd$aks$1@nnrp1.deja.com>,
> bscherer@vision.eri.harvard.edu wrote:
> > I'm using one of the LabView examples, the simple spectrum analyzer,
> > without any modifications. When I first run the program, I get
> perfect
> > resuts. How
ever, when I run the VI again, there is no signal. It
> seems
> > that the analog input is no longer working. If I reboot the computer,
> > it again works one time.
> >
> > I checked my signal with a scope, and it is still there. I've tried
> > using a different analog input pin in case the one I was using was
> bad,
> > but that didn't help. I've also tried running a very basic analog
> input
> > program with similar results. (Working once only.)
> >
> > Has anyone else had similar problems, or have any suggestions?
> >
> > Thanks,
> >
> > Beth
> >
> > Sent via Deja.com http://www.deja.com/
> > Before you buy.
> >
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
>
Beth,

Sounds like you may have a connection problem to your DAQ board rather than a
software problem. It's been my experience that if you have the + side of the
signal connected but the - side does not have a good connection, the signal
is floating. The DAQ cards with usually float high if the + side is
co
nnected. Maybe you should start there. I've used that same Simple
Spectrum Analyzer VI myself, and it's worked very well.

Mark



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[Keith Ryan]

wrote in message news:8hrcgd$aks$1@nnrp1.deja.com...
> I'm using one of the LabView examples, the simple spectrum analyzer,
> without any modifications. When I first run the program, I get perfect
> resuts. However, when I run the VI again, there is no signal. It seems
> that the analog input is no longer working. If I reboot the computer,
> it again works one time.
>
> I checked my signal with a scope, and it is still there. I've tried
> using a different analog input pin in case the one I was using was bad,
> but that didn't help. I've also tried running a very basic analog input
> program with similar results. (Working once only.)
>
> Has anyone else had similar problems, or have any suggestions?

It sounds as if the referenc
e potential of your signal is floating above the 10volts of the
input of the card and saturating the PGIA circuit.

In my NI Series-E card reference manual, it gives specific instructions on how to connect
various signal sources ( Floating and Grounded Signal ).. and input measurement configurations
( Differential, Singled-ended ground referenced, single-ended non references ). This is chapter 4, "Signal Connections".

If your signal is floating.. you may wish to try a balanced measurement, with a bias resistor between
the negative ACH input and AIGND.. I typically will use 1/4watt 1Mohm resistors for this purpose.


--
Keith M Ryan
Applications Engineer
JL AUDIO, Inc
Get shocked! http://www.jlaudio.com/