03-28-2013 12:35 PM
Hello All,
I am very new to labview but have found the forums and examples extremely useful. I've probably spend 50+ hours acquainting myself with tutorials and background information, but think I am at a point where I need some of your help.
I'm having trouble modifying the example "AO Frequency sweep" found here (attached as custom_sweep_1.VI ) to allow me to sweep DC voltage. My instinct is that I do not need the "Waveform Buffer Generation VI" and that I should be able to remove the inputs associated with it since I am only interested in a DC Voltage sweep. It also calls create_log_frequencies.VI, and I am fairly certain I can use it as written and just change "frequency" to "voltage." My working edits of custom_sweep_1 are attached as custom_sweep_Voltage.
The problems I am having with editing custom_sweep_1 are:
1) I don't think I fully understand how or if the parameters associated with Waveform Buffer Generation VI relate to a DC Voltage sweep.
2) Extending from 1): The for loop depends on Samples and Cycles Per Buffer and I am not sure how/if to replace these values
3) The DAQmx Timing (Sample Clock).VI gets its sample rate from Waveform Buffer Generation VI output, but I think I can just use 1/Sweep Duration to replace this (?)
4) The DAQmx Write.VI gets data from Waveform Buffer Generation, but if I can bypass this VI and wire AO Voltage directly to DAQmx Write then I think I can use Minimum Voltage as my data input (?)
5) After implementing these edits, the custom_sweep_Voltage runs but I get Error 200609:
"Possible reason(s):
Generation cannot be started, because the selected buffer size is too small.
Increase the buffer size.
Selected Buffer Size: 1
Minimum Required Buffer Size: 2
Task Name: _unnamedTask<3A>"
I'll also note that I've tried other means of creating the DC Voltage sweep VI:
1) I've tried modifying the IV Tracer example (found here), but find that it is much more confusing than modifying the frequency sweep.
2) This tutorial and sample block diagram looks straighforward, and I am also working on understanding what DAQ Assistants 1,2, 3 do.
Any/all feedback would be great. I think it is evident that at the very least, my poor understanding of "buffering" is if the cause of my confusion regarding the frequency sweep modification, so please feel free share any information you have.
Thank you so much for the help,
-Esperanza
Additional background on my project/progress using labview follows below:
My end goal is to determine whether or not the resistivity of an organic conducting sample changes with time. To do this I would like to compose a VI that sweeps DC voltage output from -5 to 5V periodically over the course of 24hrs and simultaneously measures the voltage drops at my load resistor (to determine the current through the circuit) and at the sample of interest. I am using a USB 6259 DAQmx and have properly configured my circuit. I have two working VIs that I've created using the DAQ assistant and by modifying some of the examples I found online. One outputs voltage (to an AO) but I have to manually select the voltage value. The second reads voltages across samples of interest and writes the data to a TDMS file. If you've read this far and still feel like providing input, my next goal after figuring out how to sweep DC voltage is to combine that VI with my measurement VI. I think it will be relatively straight forward, but again, I welcome any and all feedback!
Solved! Go to Solution.
03-28-2013 06:00 PM
I have solved this problem. I changed my approach to be similar to last link in my post. the AO frequency sweep approach is much more complicated than I need. Thanks for the help.
-Esperanza