2 analog inputs - Voltage and Strain - 2 DAQ Assistants?

[jrautenb]

I need to collect two different types of Analog Inputs (16 channels of Voltage and 10 channels of Strain). 

I am using:

LabView 7.1

1000 Chassis

1520 w/ 1314 for 8 voltages

(2) 1121 w/ 1321 for 8 more voltages

1521 w/ 1317 for 10 strains

Is there a way to use two different DAQ Assistants (one for strain, one for voltage), or do I have to create channels individually for either all of the strain channels or all of the voltage channels?

I tried to collect two strains at one time by creating channels individually, but was unsuccessful, it only seemed to want to read one channel at a time.

I have also made a quick attempt to use two DAQ assistants, but have not spent an appreciable amount of time on it yet.

Thank you in advance,

Jeff

Message Edited by jrautenb on 09-23-2008 10:09 AM

[Wayne.C]

Jeff,

I'll assume that because you mentioned the DAQ Assistant that you are using DAQmx and not Traditional DAQ.  If you need to read all 26 inputs at the same time, then they all need to be in the same Task.  This is because only one Analog Input Task can be running at any given time.  See the Task State Model in the DAQmx documentation for more info.

You can add multiple channels to the same DAQ assistant or you can use the functions on the NI-DAQmx pallet to programatically create the AI task.  Depending on your program, building the task programatically will usually create code that is much faster and more efficient.  There are a lot of good examples that ship with NI as well.

[jrautenb]

Yes, I am using DAQmx (although I'm not exactly sure of the differance).

I found in a different post that one can add both types of AI measurements (strain and voltage) in the same DAQ Assistant by using the 'custom voltage' option and manually setting all of the necessary parameters.  I am now able to collect all of the required channels.

However, there is now an offset in my strain measurements that I was hoping to calibrate out using the 'strain' option in the DAQ Assistant.  Is there a way to calibrate the strain gages outside of the DAQ Assistant?  Otherwise I will just have to offset it manually while analyzing the data.

I would rather use the DAQ Assistant than build the task programatically from a simplicity standpoint.  I only need to collect data at around 1Hz, so speed is not imperative.

Thanks,

Jeff

[MatthieuD]

Hi Jeff,

What you require is possible in the latest DAQmx releases.( I think DAQmx 8.6.0 does it, and is compatible with LV7.1) >> This will allow you to set up parameters per channel, the output of the assistant will still be an array... 

If you install that version, you will find that adding a new channel in the daq assistant will give you the choice of sensor that is linked to your board.

You can find the driver at ni.com/downloads. 

I hope this helps

Matthieu

Message Edited by MatthieuD on 09-24-2008 07:59 AM

[jrautenb]

This is exactly what I am looking for.  Thank you very much.

Jeff