Whey does waveform storage in TDMS channel sometimes stores without dt data? [LV 8.2]

[GS]

I'm storing waveform data in a TDMS file using the TDMS Write VI. In one app I only write the waveform data to a channel. In that app the waveform data stores with the dt (Waveform x-step width) data. In another app I store array data to a channel and also store waveform data to another channel. In that case the waveform data is saved without the dt data. Is that expected? It doesn't seem right that I should loose the dt value.

George

[NIJanell]

Hello GS,

When you store it as an array, you are going to lose the dt information.  Can you provide some additional details?  Is it during the array write or the third channel write that you are losing the dt value?  Could you please post some sample code that will reproduce this issue?  The smaller, the better.

Thanks!

Janell R | Applications Engineer

[GS]

The cause of the problem may be somewhat different than what I thought although the outcome is the same. I built a very simple VI to test it (see attached). In this VI I'm storing waveform data types in two separate channels. The first channel is being store as an array (Wavform property displays as "No") and the second channel is being stored as a waveform (Wavform property displays as "Yes").  Thye both should have been stored as waveforms. I'm baffled why that get stored differently.

George

[Matt_W1]

The difference is that your not passing NI_UnitDescription to the second waveform (and seting that property is what breaks the waveform in the tdms). To use NI_UnitDescription use Set Waveform attribute instead.

Message Edited by Matt W on 11-09-2006 05:46 PM

[GS]

Thanks. I never would have guessed that one.

George