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Multiple Daq assistant in sequence

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Multiple Daq assistant in sequence

Hi,

 

I am a complete new user of labview.

I am trying to take a calibration reading from a load cell to calculate an offset, followed by a test with the offset removed. My attempt at creating the block diagram falls over at the second instance of daq assistant.  What am I doing wrong?

I have attached the block diagram, I know there are a few loose ends but once I have solved the acquisition issue I will export data to a report.

 

Thanks in advance

 

 

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Re: Multiple Daq assistant in sequence

What do you mean by "fails"?  Do you get an error code or other message?  Does the computer blow up?

 

Please attach your VI.  Express VI's hide details of how they are implemented.  Those important details that determine whether it works or doesn't work can't be seen from a screenshot.

 

I'm going to use Jeff's crystal ball and say that you are getting error -50103 about device being reserved, and that it is because you have the DAQ assistants set up for continuous sampling.

 

You'll be better off  if you start learning now the DAQmx primitive functions

Getting Started with NI-DAQmx: Main Page

 

 

 

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Re: Multiple Daq assistant in sequence

When the guy from NI Sales comes to your school with a bunch of cDAQ equipment and sets it up for a Demo to convince you to use LabVIEW, they give you a thermistor or an accelerometer, say "Hook this into pins 1 and 2", show you how to drop a While Loop, the Dreaded DAQ Assistant, a Chart, and a dynamic wire to the Chart, and say "See how easy it is to gather data with LabVIEW!".  Then they leave (and take their equipment to snooker another class).

 

If you want to do something other than a simple "gee-whiz" demo, you need to learn to avoid the Dreaded DAQ Assistant and its Evil Twin, the Dynamic Data Wire.  NI has some great tutorials on DAQ and DAQmx.  You can find one of my favorites by doing a Web search for "Learn 10 Functions in NI-DAQmx" and reading the White Paper that pops up.

 

You do not want multiple DDAs in sequence.  You probably do want multiple (parallel? interacting?) DAQmx sequences to handle the multiple tasks you want to do.  You might consider developing them one at a time and testing them independently before trying to make them work together.

 

Have you tried playing with MAX and your device to understand how your device works and what kind(s) of control you have over it?  To understand the various sampling modes, and how they interact (such as # Samples, Sampling Rate, and how often new data appear)?  Play with your device, write some simple non-DDA DAQmx code, and come back either having solved your problem (and giving yourself credit for finding the solution) or asking a more focussed question.

 

Bob Schor

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