running multiple DAQ tasks at the same time

[DAQ_noob]

I am trying to setup a program that would allow me to run different analog voltage waveforms on different channels.

The rate at which samples hit each channel can be the same for all 32, but I want each to be sourced by an individual file I/O source.

I saw the multiple tasks thread and I did try doing the multiple task approach first and needless to say got the same error.

Saw something about software timed approach working better, but it is still a bit unclear in that post. Can i do with this card what I described above and if so is this software timing approach the way to go?

Thanks in advance!

[Gerryli]

Hi,

i am not sure i undersand you prolem correctly, it looks you want sampling data from all channel available in DAQ card,

i think you can use the scan function to do it instead of mulitiple DAQ task; ( seach sampleing mulitple channel example)

however, tasks need occpay the resource of DAQ board. in other words it is depends on the AD convert in board. if you only have one AD then you only can run one task in time.

Hope can Help !

B.R

Gerry

[DAQ_noob]

I need to generate different voltages, not sample signals. I am using DAQ card as a signal source, not sink.

[jschwartz]

Hi,

What DAQ device and and programming language are you using, i.e., LabVIEW/CVI/.NET?   If you are new to DAQ, a great place to start are the example programs.  You can find the example programs with the Example Finder, located at Help >> Find Examples in both LabVIEW and CVI.  Once this opens, double click Hardware Input and Output >> DAQmx >> Analog Generation.  This will have many programs for generating waveforms. 

[DAQ_noob]

I am using Labview 7.1.1. So far I am using DAQ assistant to generate me a VI, which I then edited by replacing some stock ramp function with file I/O as waveform data source. Unfortunently every channel in the task gets hit with the same waveform and I need to be able to generate completely different and arbitrary signal on each channel not constrained by any mathematical function.

I will look through that example, thanks.

[jschwartz]

Hi DAQ,

I thought you were programming in a text based language because you posted in the LabWindows/CVI forum.  I have included a LabVIEW example that should be helpful to you.

NI-DAQmx: Continuously Generate Multiple Waveforms  

[d_tinman]

Jim,

I am doing something similar to you but I do not have the threadsleep and I seem to have an issue with some kind of interference between the input and output channels.  How critical is the threadsleep and what is a rule of thumb for setting it?

Using a 9172 chassis, two 9205 modules and one 9264 module.  I am acquiring data from four accelerometers and 12 LVDTs.  I am processing the accelerometer information and sending the calculated displacement waveform as an output to the 9264 module.  First version with the input only was working properly.  As soon as I added te output task, the input data was reading bad numbers and it felt like there was intereference from the output channels.  Appreciate your feed back

Tinman

[enderWiggin10]

Hi Tinman,

What slots do you have your modules in on your 9172?  Are you acquiring your data on the 9205 modules in differential configuration?  What do you mean by bad numbers?  Does this refer to noise, an offset, etc?  Differential inputs can help to eliminate interference if it is on both the positive and negative input lines.

Best,

[d_tinman]

Adam:

9205 is in the first and second slot.  9264 is in the third slot.  9205 acquires the voltage in the differential location.  When I say bad numbers, it feels that the 9264 output module is interfering with the 9205 module.

I am going to retry fresh this coming week based on the inputs but I was trying to make sure that I was not overlooking an obvious fact

[enderWiggin10]

Hi Tinman,

Please keep us posted on the progress.  Here is a great Developer Zone document that also discusses how to eliminate noise on signals.  Do you get noise on the inputs when the output module is not outputting, or only while you are outputting a signal?

Best,