How to read a part of a TDMS file?

[Carlz]

Hi,

I'm having problems loading back a part of a TDMS file.

Im currently trying to use the offset and count input on TDMS read.

But the offset value doesn't seem to make any difference: If I set offset to 5 and count to 10 it still puts out 10 data points.

By the way:

Im using labview 8.5, and I multiply the offset and count with the sample rate (100000samples/s) so that offset and count settings input will correspond to seconds of measurement to load.

I would be very grateful for any help

Regards

Carl Zandén 

[Carlz]

Please, is there someone who can help me? 

[RoyA]

I am new to TDMS as well so take what I say with a grain (block) of salt.  But as no one else has answered, I'll give it a shot.  First of all, at 100000 S/s and an input for COUNT of 10 X 100000, you will always get 10 seconds worth of data.  Your graph is not showing you 10 data points, it is showing you 10 seconds OF data.  This is expected behavior.  By varying the OFFSET input as you have it you will step through your data 5 seconds (5 X 100000 points) at a time.  So, for IN offset =0 you will see data from 0 to 10 seconds, for IN offset =1 you will see data from 5 to 15 seconds, for IN offset =2 you will see data from 10 to 20 seconds, etc.  You also will probably NOT see the X scale change accordingly as it has no way to know what the initial time of your data set is, unless you tell it.  All it knows is that it has a set of 1M data points with a 1e-6 second delta t.

Hope this helps.

Roy