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PCI 6723 at 100KHz

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Hello all

 

I am using NI PCI 6723 Analog Output card along with SCB-68 Connector box. The specifications of PCI 6723 tells that maximum sampling rate (update rate) of single channel is 800 Ksamp/s. I  tried t0 generate 100 KHz sine wave using single channel only in continuous mode with +/- 10V amplitude set using Labview Signal Express application, however output from DAC was very distorted (kind of triangle waveform instead of sine waveform) and even output amplitude reduces to around 2 to 3 V and becomes non symmetric (i.e. not centered around 0V).

 

Then i found that upto 20KHz signal generation, DAC output was very fine without any amplitude or shape distortion, however as i go beyond 20KHz (with constant update rate of 800Ksamp/s)  towards 100KHz, DAC output started to become more and more corrupt.

 

Kindly tell me if NI PCI 6723 is sufficent to output 100KHz signal if i use only single channel?

 

And if yes, what can be the reson for this distortion?

 

Thanks

 

Best Regards

Asim

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How are you measuring the output of the 6723 card?

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Solution
Accepted by topic author ASIM_BHATTI

It looks like you're exceeding the maximum slew rate for the card, which is likely why you're seeing the distortion on your waveform. Slew rate is defined as the maximum rate of change of output voltage per unit of time. The card (from the manual, linked below) has a maximum slew rate of .7V/us, are you're exceeding that by a significant margin.

 

NI 6722/6723 Specifications

http://www.ni.com/pdf/manuals/370822c.pdf

 

To remedy this, you can either decrease the frequency of your output waveform or you can decrease the amplitude of the waveform; both changes will have the effect of reducing the slew rate. You'll need to reduce one or the other enough to come into line with the card's specified maximum slew rate.

 

So, long story short, the card is not capable of outputting a full scale sine wave at 100KHz due to the limitation of the maximum slew rate. You should be able to output a 100KHz signal if you reduce the amplitude of your waveform.

 

Regards,

Ryan K.
Product Manager, ATCA and BEEcube
National Instruments
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Thanks for reply. I am using Agilent oscilloscope for measuring DAC output

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Thanks for your help. Can you kindly suggest any suitable NI DAC for 100KHz and 450KHz signal output?

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