This Document is not yet Rated

Rate this Document

Searching on Certain Channel Properties Returns no Results for TDMS Files

Primary Software: DIAdem
Primary Software Version: N/A
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
When I load a TDMS file in the data portal, DIAdem shows channel properties such as "minimum" and "maximum"; however, when I create an advanced search and add a condition for the "minimum or "maximum" to be greater than, equal to, or less than the value in the file, no files are returned in the search results. Furthermore, if I save the data as a TDM file instead of TDMS, the data finder is able to find the new file with the same query. How can I search TDMS files on my computer based on certain properties?

Solution:
The TDMS file format only stores two properties automatically*: NI_ChannelLength and NI_DataType. The TDM file format, on the other hand, automatically stores a host of properties, including minimum and maximum as in the above example. This is a direct result of the buffering paradigm of each file format. The TDM file expects you to have all the data in memory at one time before saving the file, while the TDMS file expects you to save one buffer after the other.

Furthermore, the TDMS file VIs in LabVIEW are intentionally kept lean and mean so that you can achieve maximum streaming speed. Automatically calculating anything when writing each buffer to disk, however practical or useful it might be later, is categorically eschewed.

As a matter of convenience, DIAdem automatically calculates the following four derived properties any time a channel is loaded into the Data Portal (so that it knows how to quickly plot the channel):

• minimum
• maximum
• novaluekey
• monotony
  

In other words, if the file a channel comes from does not have these properties stored, DIAdem  automatically calculates and displays them at load time. This can make it appear that the TDMS file stores these properties when it actually does not (unless you specifically program it to).

Unfortunately, the DataFinder knows nothing about these derived properties. Instead, it must rely entirely on the properties as declared (or not declared) in the data file. TDM files are guaranteed to have the minimum, maximum, and other properties declared, which is why re-saving the TDMS file as a TDM file will result in finding it with the DataFinder.

*unless writing a waveform channel, in which case the "wf_" properties are added as well

Related Links:
KnowledgeBase 3LDLKN9F: Creating Custom Properties for TDM Files in LabVIEW

Attachments:





Report Date: 07/16/2007
Last Updated: 08/02/2007
Document ID: 4BFDBPSN

Your Feedback!	Poor  |  Excellent							Yes	No
Document Quality?							Answered Your Question?
	1	2	3	4	5
Document needs work? Please tell us why.
Please Contact NI for all product and support inquiries.