AI LVDT Minimum and Maximum Inputs - What are they physically?

[RVallieu]

I am trying to configure an SCXI-1540 to read an LVDT with 5.1282 mV/V/.001 inch sensitivity.

The inputs to Maximum and Minimum are not clearly defined in the AI LVDT help file, nor in the 1540 manual.

What do these inputs to the DAQmx VI mean REALLY to my physical system?

I thought that they were supposed to be the actual Vrms ranges I would be trying to measure on the LVDTs, calculated from

MAX = Vrms = (V Excitation)*(Sensitivity)*(Max range in mils)

MIN = Vrms = (V Excitation)*(Sensitivity)*(Min range in mils)

The LVDT I am using is measures -.04 to 0.04 inches on either side of the null reading.

How do I convert what I have in my physical set-up to programmatically determine the Maximum and Minimum inputs?

I get error -200077

DAQmx Start Task.vi:3<append>
Property: AI.Max
You Have Requested: 625.536000e-3
Valid Values Begin with: -383.670964e-3
Valid Values End with: 383.670964e-3

Channel Name: SC1Mod2/ai0

Task Name: LVDTsPositionTask

That error was obtained after just setting Min to 0 and Max to the expected Vrms maximum.

Are these values used by AI LVDT to set the gain?

If I have 4 LVDTs, can they all be included in one task, and have similar but not identical Vrms?

[RVallieu]

Ok looking at the Example Cont Acq LVDT Sample-INt Clk-SCXI 1540.vi

These are supposed to be the physical distances expected to be measured.  OK.

One LVDT works...with the Max and Min set to 0.04 Max and -0.04

The problem now becomes if I try to create a task with multiple LVDT channels from the 1540.  It won't let me set individual sensitivities for each LVDT in the task it seems, even though every LVDT is different and has a slight variation on sensitivity.  Should I just use the maximum sensitivity out of the 4 gauges to allow the AI LVDT to set the gain for all the channels?  Or do I need to bust out the channel property nodes and configure every one of them seperate in a loop?

[RVallieu]

I have a feeling I can not set the channels this way 😉 - even though the settings are all the same....

Are any of the settings allowed to be different, i.e. different Excitation Voltage on different LVDTs?  Or is my problem trying to use 1 task with 4 LVDTs?

Do I need to configure individual tasks per LVDT?  Is that even possible?

Message Edited by RVallieu on 03-19-2008 11:41 AM

Message Edited by RVallieu on 03-19-2008 11:42 AM

[RVallieu]

OK - now it is working - I think I had run the task once without clearing it before calling create task again.

I have not tried setting different sensitivities yet, but making progress

[mallorim]

Hi Ryan,

Something you might try to set the sensitivities on each channel, though I am not sure it will work, is having multiple DAQmx Create Channel functions for one task, as can be seen in the image below. On each create channel, I set different maximums and minimums and it ran without error.

Regards, Mallori M.

Message Edited by mallorim on 03-20-2008 01:18 PM

[RVallieu]

As stated above I got my original code to work fine.  I had a duplicate task name that was not cleared causing the error.  The loop is not a problem.