Multiple Channel Express DAQ Assistant Multiple Sample Rates

[smoothdurban]

Hello,

I am trying to acquire multiple signals utilizing different sample rates.

I have 4 K type thermal couples I would like to record at a lower rate then a load cell.

CUrrently I have all of these channels configured in Express DAQ assistant but I would like to acquire different sample rates for each type of signal.

I am using a PXI 1052 Chassis along with a 1102 Module for thermal couples and a 1520 module for my load cell.

ANy help would be appreciated.

[Ryan-C]

Hi there,

Do the channels need to be synchronized?  Or is the timing between the four channels not as crucial to the data acquisition?

[smoothdurban]

They could be in separate files as long as I could import them into DIAdem and stitch them together.   I would assume this would be possible as long as both files use a absolute time stamp.

[Carisa_L]

Hi smoothdurban,

I believe it will be difficult to implement this with DAQ Assistants. I would recommend using the DAQmx APIs. I've modified one of our examples to help you get started. Hope this helps!

Best,

Carisa

The attached Code is provided As Is. It has not been tested or validated as a product, for use in a deployed application or system, or for use in hazardous environments. You assume all risks for use of the Code and use of the Code is subject to the Sample Code License Terms which can be found at: http://ni.com/samplecodelicense 

[smoothdurban]

Any chance you could save this example in v2009?

[smoothdurban]

It appears the example was able to allow me to acquire data at different rates,

Now I would like to write the data to file at those different rates.

So a file with temperature recorded at a Hz and a file with load recorded at 500 Hz.

Any ideas?

[smoothdurban]

Hello

I have tried the modified example and it appear the DAQ rate of the first DAQmx timer is truncated by the second timer.

So the temperature channels are set to 10 Hz and the strain measurement channel is set to 500 Hz.  When I try to write this data to a file using  Express write measurements to file the data written to file uses the last sample rate so in this case 500 Hz.  I am trying to avoid recording certain data at a higher and unnecessary rate.

[Ryan-C]

Hi there,

Which version of LabVIEW are you using?

Checking out the Detailed Help for the Write To Measurement File Express VI, it looks like you want to make sure that Segment Headers is set to One header per segment, and that X Value Columns is set to different acquisition rates.  Can you verify this?  See the documentation here: http://zone.ni.com/reference/en-XX/help/371361H-01/lvexpress/write_lv_measurement_file/

Best,

[smoothdurban]

Hey Ryan,

I am using LabVIEW 2009

I have made the changes as you ahve suggested and I still seem to get the same rate between channels

Here is a screen shot of the setting in my Write to File Measurement.

I have also included an image of the data

[Ryan-C]

Hi again,

Perhaps you could post a screenshot of your LabVIEW code?  It seems like you're doing everything right, so maybe taking a look at the code will help.

Thanks,