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Single Point Acq Sample Rate
Solved!
Sousuke
06-30-2009 02:00 PM
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Hello, a little info about my system and myself to start. I am running LabVIEW 8.6 and using NI USB-6259 as my DAQ device. I am new to the LabVIEW world only having been using this setup for 3 weeks (but a nice step up from the Win95 system I was using).
I am trying to control and circuit running at 8kHz. I wish to read in a voltage from the circuit, detect a zero crossing in its derivative, and then send output a voltage back into the circuit based on its sign at those crossings. To safely control the circuit I need to be able to sample well above 8kHz.
The issue I am having relates to the limits in speed due to a loop based around a "1 Sample (On Demand)" DAQ Assistant. I have read lots of posts saying to use HW Timed sampling but I don't believe my DAQ device supports this. I have used clocks to get a rough idea that my loop is running at roughly 25Hz.
I am not sure if the problem is in inefficient coding or limitations of my hardware and software. Attached you will see my current VI.
Solved! Go to Solution.
falkpl
06-30-2009 03:13 PM
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You are correct you are using the softwared timmed acquisition, you want to run in continious mode, The 6259 should be able to acquire upto 1.25 MS/s. Try setting this up with daq assistant since you are new to labview, or look at the analog acquisition examples. you will essentially want to read in a loop using continious buffered acq, then pass the results to your processor vi or slave loop. I would sampel at 5-10 times the 8khz to get a good representation of you signal. faster than 10x will not give you anything except too much data to process. 8Khz is not too much data and you might be able to process this in the same loop as your daq read.
07-02-2009 10:40 AM
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As closure to this post:
After a 3 hours phone conversation with NI, using the hardware and software I have, the application is out of the question. The problem is in the fact that a non real time (RT) system can't hope to process any buffer of continuous sampling fast enough to have a feedback loop back into that circuit.
