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DAQ USB-6009 Analog Input accuracy issue

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Hello,

 

I have an issue in which I am trying to read in a temperature signal (10mV/degC) using the USB-6009, but have run into an issue of accuracy in the input signal of the DAQ device.  The temperature at room temperature reads at a steady 230mV (23degC) using a multimeter device, but with the DAQ device I am seeing the signal bounce around at +- 25mV, which greatly effects my work. 

I hoped that someone would have a solution to this as my brief search of the forums turned up nothing.  Is there a way to average out this wide band in input signal measurement or any way to resovle this??

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Hi mdzz,

 

I would first make sure that you are measuring differentially on the ±1 V range of the 6009 to get the most accuracy possible from the DAQ card.

 
It's common for DMMs to implement some sort of averaging to obtain a more stable measurement and reduce system noise.  This isn't done on our DAQ cards which are often used to measure fast-moving signals.  Implementing your own averaging in software would be a good idea in your case.  For example, you can configure a HW-timed measurement @10 kHz, read back 1000 samples per loop iteration and average them together to get a more stable result that would still update 10x per second.

 

 

Best Regards,

John Passiak
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Thank you for your help John P.  Could you provide an example on how to configure a hardware-timed measurement using the usb daq? 
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Solution
Accepted by topic author mdzz

Hi mdzz,

 

What development environment are you using?

Here's a LabVIEW example that should do what you need.

John Passiak
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Hi mdzz,

 

JohnP has posted a great example for this.  You could also use a LabVIEW DAQmx shipping example for this, with a little modification.  You can locate this example in LabVIEW by navigating to Help»Find Examples...  and then selecting Hardware Input and Output»DAQmx»Analog Measurements»Voltage»Cont Acq&Graph Voltage-Int Clk.vi.  You can then specify the sample clock rate (Frequency) and Number of Sample per Channel (Number of samples to be averaged each iteration).  Also, you will want to average the array of data that is output from the DAQmx Read inside of the while loop by inputting the Data Array into Mean.vi, which is located by navigating to Functions Palette»Mathematics»Probability and Statistics»Mean.vi.  The output will be a single value, the average of the array, which you can graph or log.

 

Best,

Message Edited by cyclone2k9 on 04-23-2010 10:51 AM
Adam
Academic Product Manager
National Intruments
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thank you both, your information helped a great deal and resolved my issue.
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