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ADC200/20

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ADC200/20

Postby Guest » Thu Sep 16, 2004 10:51 am

Hi
i have a ADC200/20 PC-oscilloscope.
i use labview to trigger it, but there is always a significant offset of up to +-5% of the range on that signal, this offset is there during the whole taken block of data.
i tested it with your triggering example too, same thing.
however i recognized that when i use both channel there is no significant offset, but i dont want to do that, because i want the highest sampling rate i can get.

i didnt get this problem on picoscope.....i think it automatically activates both channels?
Guest
 

Postby Sarah » Thu Sep 16, 2004 2:32 pm

Hi

I am sorry to hear that you have been experiencing this problem.

The most likely reason that you are seeing this offset is because there is an offset on channel B. When you trigger on channel A it actually goes throuh channel B and if there is an offset there it will pick it up. Picoscope might not be seeing it if you have performed an "offsett null".

Check the voltages again carefully in Picoscope (be sure to have it in DC mode) and see if the error is as you said ±5%. If it is then this is outside of the specifications and you can send the unit back for recalibration. To do this, email us your full contact details and the details for the unit, specify that it needs recalibrating and we will send you a returns number. Please do not send us the unit without obtaining this number.

If it is not offset by as much then you might be able to write some programming to perform an offset null in your software.

Hope this helps

Best Regards
Sarah
 

Postby Guest » Fri Sep 17, 2004 1:01 pm

There is no signal on channel B, i just use channel A. But why is there a offset on channel A, when i dont even use channel B and there is no signal plugged.
but when i activate channel B...still no signal plugged to it, then it is gone.
i always trigger on channel A.

I dont think there is a damage, as it is working good in Picoscope.
how can i do an offset null in LABView? this wouldnt explain my problem, but solve it.

thanks for your help
Guest
 

Postby Sarah » Fri Sep 17, 2004 3:16 pm

Hi

Thank you for your post.

The reason that an offset on channel B would be shown when triggering on channel A is that when triggering on channel A, the signal gets routed through channel B (as this is where the triggering hardware is located). This could be why you aren't seeing the problem when channel B is activated.

To create an offset null, you would need to take some readings when the input is shorted (or terminated with 50ohms) and then average these to calculate the offset. You then compensate all subsequent readings by this amount.

Hope this helps

Best Regards
Sarah
 


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