picking data from a tdms file in a main VI

[unr]

Hi There

This is what I am trying to do, i have a power detector which has to be calibrated by applying a RF signal to it and doing the power sweep from -50 dBm to 0 dBm, i get voltage vs power(dBm) values. Now i have a main Vi where i need to know if i have any voltage value, how much will be the power value form the earlier data that i stored in a TDMS file. For that definitely i have to have some kind of call function to pick the right value form the graph or data by doing some kind of interpolation which will give me corresponding power value looking at the voltage value. How could this be done in LabView? what functions or subVI should i use?

I am using labview 8.2, i have a DAQ 6259 usb card. thanks in advance

Regards

Sam 

[Hillman]

Hi Sam,

Your TDMS file should have two columns/channels - one containing your range of voltages (x) and one containing your range of power (y).
Then if you read in this TDMS file (see help>> find examples >> search TDMS >> Read Channel Groups TDMS). (Also a good one about writing channels too.)

You could then separate the two columns, - using array subset or re-sizing your array,
Search the array containing your voltages (x) using the Search 1D Array function to return its position (index),
then use the index array function, using the value returned on the second array containing your power readings (y).

Then you'd return the matching value of power for the given voltage. This is very similar to interpolate (which there is a vi for) but I am not familiar with it.

This is at least how I understood your post. However, if not, continue to post and i'll check back later.

Thanks,


Message Edited by Hillman on 08-05-2008 11:23 AM

Message Edited by Hillman on 08-05-2008 11:24 AM

Message Edited by Hillman on 08-05-2008 11:30 AM

[Hillman]

Hi again,

also you can (for time sake) use an express vi to read the TDMS file, use a signal splitter, and then a convert from express to DBL vi. Then just search through the separate arrays like i mentioned before.

Thanks


Message Edited by Hillman on 08-05-2008 12:02 PM

[unr]

Hi Hillman

I have done the same thing like you said and it does give me preety accurate values. But what i need to do is saving the whole data in some kind of file for using it in main VI. My main VI has voltage sliders which i change to get the voltage values. Now this value has to be connected to some kind of logic to read the corresponding power value from the saved data automatically and give me the power value which i can store.

The logic in the main VI should be to compare the voltage value that i get from the slider and compare all values in the table and give me the corresponding power value.

I am attaching the snapshot of the graph. The Y value on the right side of the graph tells me the corresponding dBm value when i enter a constant voltage value. This whole logic has to be moved to another VI where i will connect it to the value of y voltage slider. Hope i made myself more clear this time.

thanks for the help

sam

[unr]

Hi Hillman

I think I can make it work now. I think the read from measurement file.vi in the  file I/O palette should make it work and then getting the output value which i need from the bunch of values is easy and i already did that, which is same like you suggested. so I think can can wrap it up from here.

thanks for the help.

Sam

[Hillman]

thatz grand, i was about to reply - but if you think your good to go then thatz grand. No problems!

good luck