How to find best sampling data acquisition rate for my NI DAQ Board? What is Sampling Clock DAQmx?

[UmairMech]

Hi,

One of my senior developed code for microscope data acquisition. My work is to purchase the DAQ board based on our requirement. Currently we are using USB 6363 device that sampling rate is 2.0MS/s. This is too much for our system and due to its high specifications device is very expensive.

I want to know how fast sampling rate is required for my device, let suppose if 50,000 samples is enough then I can go for 250KS/s device etc. For this purpose I find out that following VI (attached as scanningvi) is used for sampling rate. But I don't know what is meant by rate and resolution in my scanningvi (image attached). For rate I can change it and my senior mentioned it as a sampling frequency. Resolution is set as 2048. This is decided in sample clock vi 🙂

The second image shows front panel with two data graphs one is captured with high rate and other is captured with low rate. 

[Kevin_Price]

You forgot to attach the code (and when you do be sure to first save back several LV versions to 2019 or so).

Also, please describe more about your system and purpose.  If I had to guess, I would venture that your most basic tradeoff will be among resolution, sample rate, and overall experiment throughput.  For example, perhaps you need to generate a 2048x2048 image based on capturing 1 sample per "pixel."  Thus you need ~4 million samples and the time required to capture them will depend directly on your sample rate.  So a device capable of 2 MS/s could complete this task in 2 seconds while a device running at 50 kS/s would require 80 seconds.

*Probably* that's the kind of trade off you'll be facing when you consider a cheaper and slower DAQ device.

-Kevin P

[UmairMech]

Hi @Kevin_Price

I have attached the code in 2017 version.

The image I acquire using my vi is currently 256x256 pixel. I have options of 512x512, 1024 etc. but we don't use these option to acquire the image. For now just consider 256x256 and 512x512.

For me acquisition time is most important. I am acquiring the measurement data from an analog sensor to construct the topology (image) on the labview. Its a kind of microscope called AFM, the image is constructed from x,y,z data points. x,y data points are already available to labview and i acquire z-axis data on Analog Input channel of my USB 6363. I hope it will be helpful. Secondly I didn't understand why 4 millions samples will be required for this job.

The maximum frequency range of z-axis is 20Hz, but let suppose it is 50hz or 100hz then how can I calculate samples? 

[Kevin_Price]

I don't know your equipment or your domain of study, so I'd need you to describe things in a lot more detail.

2 brief things I can say in the meantime:

1. The 4 million samples I mentioned arose from my guess at what you might be doing.  I thought maybe it was a pixel-by-pixel capture of an analog signal for an image at a resolution of 2048x2048 ~= 4 million pixels.

2. At some level, if you're doing an analog capture then there's inevitably going to be an equation that relates sample rate, acquisition time, and total samples acquired.  Namely:  Acq_Time =  Total_Samples / Sample_Rate.  Once you've chosen 2 of these values, the 3rd is determined by math.

-Kevin P