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how to increase the resolution of the daq

Hi

I am using NI 6025E DAQ card for aquisistion and generaton. Analog input resolution of the card is 12 bits for input range lmits of -10V to +10V. If I set the limits to lower value, for exampe 0V to +10V, will it increasse my resolution of the aquired signal? 

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Hi suni,

 

How are you doing!

 

I am afraid the simple answer is no. The 6025E only supports bipolar analogue input ranges as shown in the datasheet, which means, even if you explicitly choose your input limits as 0 V to +10 V in your VI or MAX, you are still using only half of the range of the ADC.

 

To increase the resolution, it is important to understand the actual range of the signal you are measuring. For example, if your signal is about 0 V to 4.5 V, the ADC of 6025E will automatically select the second input range which is -5 V to +5 V when you specify the limits as 0 V to +4 V in your VI or MAX. In this case, your resolution will be improved from 20 V / 4096 =  4.88 mV to 10 V / 4096 = 2.44 mV.

 

Hope it helps,

Message Edited by Mark M on 10-09-2008 10:44 AM
Best regards,

Mark M.
Applications Engineer
National Instruments UK & Ireland
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Hi Mark,

I am doing fine. How are you?

 

Thanks for the reply. Your information was very helpful. The signal I am measuring is about +0V to +10V. Does that mean 6025E will select -10V to +10V input range if i select limits as +0V to +10V in my vi? Or can I use custom scaling function (Y=mX -5) and  bring input signal  down by 5V therefore my input signal is now -5V to +5V and let the 6025E to select -5V to +5V range? That way I can get more resolution. Thanks very much for your help

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The scaling you are talking about is a software function and does not affect your input signal at all. Have you tried ac coupling your signal? This would have to done externally as I don't believe it is a hardware option for the board.
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Hi

Thanks for reply. I read in labview help under measurement fundermentals and it said that set the limits of siganl measured after custom scaling( under minimum value). I am kind of confused about that statement. Like you said custom scaling is a software function. I am using SCB-68 to connect siganls. Is there anyway i can use scb-68 to set up a ac coupling? 

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You have the breadboard area to add whatever you want. Read this
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