DAQmx Timing Issue

[R Redford]

I am working on a nuclear magnetic resonance project and need to take samples at a high rate from my USB-6009 DAQ.

The specific part of my program that I am having issues with does two things

1) Outputs an increasing then decreasing voltage from 0 to 5 to 0 Volts (which is connected to a power supply, though this is irrelevant to my question.)

2) Wait's a specific amount of time (around 10ms)

3) Reads a voltage coming out of a Lock-in Amplifier

The way I have the program written, I can't sweep through quickly enough (I am hoping to be able to read 200 samples and write 200, in alternation, in about 1 second). I have included a picture of the particular part of my program. After investigating further into this problem I have found that the limiting factor is the Read Voltage VI in the flat sequence structure. It takes much longer to run just the Write VI than the Read VI.

I know one solution is to use two DAQ's and the timing VI's, however, I need to know that it is reading then writing and never doing a read, read, write, for example.

Is there a way to make a reliable, fast Read/Write loop for what I need to do?

Thanks

[Broken_Arrow]

Did you set up a Sample Clock upstream? What is it set too? Maybe it is waiting on available samples. What you are doing is not terribly fast (200 reads and 200 writes in a second).

Did you know that the For Loop will iterate by the number of elements in "V" and not "Number of Steps"? Don't auto index AND wire the N terminal!

[NIquist]

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@broken Arrow wrote:

Did you set up a Sample Clock upstream? What is it set too? Maybe it is waiting on available samples. What you are doing is not terribly fast (200 reads and 200 writes in a second).

Did you know that the For Loop will iterate by the number of elements in "V" and not "Number of Steps"? Don't auto index AND wire the N terminal!

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Yes, we need to see how you configured your DAQ task to see if there are problems.  This is not enough info.

BTW, if you wire a for loop's count terminal AND index it, it will iterate based on the smallest value.  Wiring a 10 to a for loop that is auto-indexing a 5 element array will get you 5 iterations.  So will wiring a 5 to a for loop that is auto-indexing a 10 element array.  Same goes for multi-indexed loops.  The loop runs until ANY input array runs out of data (or the count is reached).

[Broken_Arrow]

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@NIquist wrote:

BTW, if you wire a for loop's count terminal AND index it, it will iterate based on the smallest value.  Wiring a 10 to a for loop that is auto-indexing a 5 element array will get you 5 iterations.  So will wiring a 5 to a for loop that is auto-indexing a 10 element array.  Same goes for multi-indexed loops.  The loop runs until ANY input array runs out of data (or the count is reached).

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Good clarification NIquist, appreciate it.