voltage signal is cut off

[philipp.busshardt]

Hi,

I am recording a voltage signal in continuous mode and set the min/max-values to +/- 10 V. But the signal is always cut off at approximately +/- 6 to 7 V (it is not exactly the same value in different recordings but it is always constant during one recording). I haven't found any solution to this problem.

I work with SignalExpress 2009.

Thanks for your help,

Philipp

[Suse]

Hi Philipp,

which hardware do you use?

Which samples and rate did you choose? For example you can use 100 Samples with a Rate of 1kHz. Please notice that the rate has to be the factor 10 greater than the samples. Did you choose continuous aquisition and differential?

Let me know if these informations helped you!

Best regards

Suse

[philipp.busshardt]

Hi Suse,

thanks for your answer. I work with the NI 9215 USB and upstream differential amplifiers, and so far I recorded 1k samples with a rate of 1kHz. I did not know that they should differ by a factor of (at least) ten. Why is that so? And if I do so, it is not possible to change the x-axis scaling, even without selecting "auto-scaling". I can only see 100ms at once. Isn't it possible to see the sampled data continously over a wider range of time, for example set the x-axis to show always the last 1 minute of sampling?

But to the initial problem: Your solution unfortunaltely does not help, I still get the signal only between approx. +/- 6V. I chose continous and differential mode in the configurations menu.

Best regards,

Philipp

[DFGray]

Philipp, the 9215 has a fixed range of +/-10V, and the actual range is a bit more than that to allow for calibration.  From the description of your problem, I would guess that the problem is your amplifier. What type of amplifier are you using?  Can you use an oscilloscope and look at the inputs to the 9215 to see if the signal is being clipped before it goes into the 9215?  You may find your amplifier is saturating.

[Suse]

Hi,

I have some additional informations for you which hopefully answer your questions!

"Field Wiring and Noise considerations for analog signals": https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

"how is the actual scan rate determined when I specify the scan rate for my data acquisition":https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P83OSAS&l=en-US

 I also tested a data acquisition in Signal Express 2009 for you and my data isn't cut off. (see attachment)

Do you need any other informations?

Best regards

Suse

[philipp.busshardt]

Hi,

I have WPI extracellular amplifiers (ISO-DAM8a and DAM80) and I have the problem with the cut-off with both types of amplifiers.  But I took your advice and tried the same with an oscilloscope and I do NOT have this cut-off with the oscilloscope. So the problem should not be the amplifiers but I cannot figure out where the problem is.

But thanks so far for your help,

Philipp