Internal connection of DAC and ADC of NI daq device

[Mojtaba67]

Dear researchers and engineers,

I am trying to implement a recommendation from a journal paper, however, I have faced a problem that I could not yet find a solution for it.

To elaborate more, I want to excite an electrical circuit and measure its response. Then I should calculate the DFT of both excitation and response signals. Eventually I should calculate the frequency response function between excitation and response.

The paper says that to prevent the discrepancies caused by DAC which is not an ideal device, it is recommended to do a calibration between the excitation signal generated by software, and the excitation signal that reaches to the circuit. The author says that he has done this calibration for NI USB 6211. To achieve this it is mentioned that”

"Before any measurement and after all the parameters have been defined, the DAC output and the ADC input are internally connected in the DAQ device, and the excitation signal is sampled and stored once to replace the excitation signal generated by the software."

My problem is that I don't know how to implement the idea that I put in the quotation.

My daq device is NI USB X 6356.

I would be thankful if you help me with this problem?

Thank you,

[ZYOng]

See Can I Perform an External Calibration for my DAQ Device in LabVIEW?

[Sara_Marmarchi]

Hi,

Have you found any solution to your problem? and can you please provide me with the journal paper you mentioned in your message?

I want to do a project and i think I have the same problem as yours. we want to simulate a nerve and then read its response to the signal. we want to use the USB6003 board but the problem is its Updating rate which is 5KHz. this updating rate is not enough for our reading and will not give us the accurate waveform we want but the problem is that the updating rate of the DAQ board is related to the board hardware so it's not something that I can change. so I thought to use a DAC for the digital to analog convertor. do you think it is a good idea? 

[Mojtaba67]

Hello,

I do not know yet how the authors of that paper, DOI: 10.1109/TIM.2009.2018693, could internally connect DAC to ADC. However, I noticed that this an be possible through a calibration process that needs some precise calibrating devices. Please find attached a document from NI explaining this procedure. For me, this procedure was not useful because of some practical issues.

As you mentioned, the updating rate which is known as the "sampling rate" in electronic terminology can not be increased for a data acquisition device. However, I think the sampling rate of your device should be more than 5kHz, which is very low. I asked a question from ChatGP and it mentioned that "The sampling rate of the NI USB-6003 can vary depending on the configuration and settings, but it typically offers a maximum sampling rate of 200 kS/s (kilo samples per second) when using a single channel in single-ended mode".

Are you sure that you have not used such a below line in your code:
%%%

set(session1, 'Rate', 5000);

%%%
Because although it is not possible to increase the sampling rate of a device, you can always decrease it.

Regarding your opinion, I am not sure that I uudrestand it correctly. So I can't tell you it works or not

[ZYOng]

From Figure 2 of the paper you shared, the ADC and DAC are not connected internally but via a USB controller. So essentially the read from ADC and writing to DAC are still done from the host PC via USB.

If you want to actual connection between ADC and DAC, you would need an FPGA-based RIO device.