How do I increase analog input speed while using single channel acqusition

[AshleyG]

I am using a DAQPad 6020E to acquire analog signal from 3 separate channels.  I am running into a problem speeding up the acqusition process.  In the multi-channel acquisition I find an odd noise artifact which looks like a RC curve.  In using single channel acqusition I must switch between the channels numerous times and switching between the channels seems to require the reconfiguration of the board each time which takes about 0.1 secs.  Using the intermediate LabView VI's I find that a task ID from the group config VI must be used in the configuration and thus each time the 'group' is redefined the board must be reconfigured.  Is there any way to speed up this process?

Thanks

[Laura F.]

Hi Ashley,

There will always be some overhead associated with switching between tasks.  The only way I see to possibly make this faster is to set up your AI config functions outside of your while loop and then inside the while loop programmatically select between taskIDs so that you are not calling the AI config function everytime you are changing the task.  I think it would be best to continue trying to acquire all 3 channels at once.  What rate are you acquiring at when you see this artifact?  Also, what input mode are you using? (i.e. differential, RSE...)  Can you give me some more information about how exactly this RC curve shows up in your data?

Thanks,

Laura

[sophie83]

I have the same problem as Ashly I think,  Im trying to run a test on my program, Im using a PXI-6071E device. When I run my program on the DAQ my input signal is soo SLOOOOOOWWWWWWWW. I dont know why because on MAX when I do the test panels it moves pretty fast.  Can someone tell me the speed of the DAQ? I am using an NI PXI-1042.

I dont know how i can change the speed of my input signal?

Any help is apprecitaed im still pretty new to labVIEW

Sophie

[Dennis_Knutson]

How are you configuring your acquisition? How many samples are you requesting? Single point or multi-point? Are you using DAQmx or traditional? Why don't you go ahead and post the VI you've written? If you run some of theshipping examples, do they run slow as well? There's a lot of reasons that your acquisition is running slow and the easiest way to find the problem is to look at your code.

Message Edited by Dennis Knutson on 07-27-2005 01:16 PM

[sophie83]

Hi, Im really new to LabVIEW so I think its just easier to post my program since I am not sure about the details with the equiptment.  I know im using Ni- DAQmx,

Basically for my program eventually I would like to take one input with 128 signals, and display them on a waveform (16 per graph), Then The user selects which signals he would like to view from the 128 using the selection tool box.  This displays the filtered signal.

Once they have aquired their desire signals, the user clicks on the toggle of the Analyze data, and they are able to choose a method of frequency analysis to analyze their signals, which is updated every second.

My program is soo slow I am nott able to run any of it, it works fine in LabVIEW but when I run it on the RT target it is very slow and pauses sometimes.

[Laura F.]

Hi Sophie,

I have looked at your VI and one reason you may have a slow progam is you have a lot of filter express VIs and any time you use express VIs you are slowing down your acquisition.  What rate do you have your analog input express VI set to acquire at?  (It is set to the default when I open it, so I suspect it is different than what you are actually using.  Double click your DAQ Assistant to open it up and look)  How are you viewing the VI on your remote target?  If you are using an internet connection, is it possible that the connection is slow and causing your front panel to look like you are missing data? 

Laura

[sophie83]

Hi, for my DAQ Assistant, Im not quite sure I understand the parameters with the clocking, you know the difference between number of samples, and the sampling rate.  Right now it is set to the default of 100 samples, and a rate of 1000Hz, so I am not quite sure what my sampling frequency is?

I dont know if you know what Im talking about, you know the DAQ- timing task, where it lists all the sampling parameters.

Also I am running it using a cable from my laptop to the NI PXI-1042 device, with an RT target?, however this RT target is always very slow for me to connect.

Sorry if its not clear, im really new to this DAQ stuff

[Laura F.]

Hello Sophie,

Don't worry, you are being clear.  I understand what you are describing.  So to summarize, the VI runs fine on your host PC, but you are having trouble connecting to your RT target.  So when you change your execution target, it takes a long time to connect?  And then once you are connected the program runs very slow?  Can you try a different program, perhaps a simple one that just collects data from one channel?  You could just open up an example.  To do so, in LabVIEW go to Help>>Find Examples to open the example finder.  Then, browse to Hardware Input and Output >> DAQmx >> Analog Measurements >> Voltage and choose a VI, maybe Cont Acq&Graph Voltage - Int Clk which will continuously graph your voltage until you press stop.  Open up one of these examples and then run it on your RT target using the method you have been using and let us know if it is still running slow.

Thanks,

Laura

[sophie83]

Yes it is still a little slow when I only run one channel.  My RT connection speed is better this week then last week, however my programs are still slow.