Number of elements in TDMS file

[knapkerd]

Is there a way to determine the number of elements in a TDMS file?  The files I am creating have several signals all of the same length.  The only way I can think of is to do this is put it in a loop and read one element at a time until it reaches the end of the file.  But, my files will have millions of elements.  Any suggestions?

Thanks.

--Robert

[Herbert Engels]

Use "TDMS List Contents" in order to find out which objects your file contains. Loop over the results and read the property NI_ChannelLength from all objects. Some objects (e.g. groups) will not have this property, but all channels will have it. This is the number of values in the channel. Add up the numbers and you're done.

Hope that helps,
Herbert

[knapkerd]

That should do it.  Thanks!

--Robert

[knapkerd]

Sorry, I jumped the gun.  I thought that I might be able to use get property from signal, but all I have is the channel name.  How do I read the length from the object? 

Thanks.

--Robert

[Herbert Engels]

It's a read-only property called NI_ChannelLength (data type is I64). You can see it in the TDMS File Viewer. Make sure to check the "found" output on "TDMS Get Properties", because groups and empty channels don't have that property.
Herbert

[knapkerd]

Works great.  Thanks!

--Robert

[Klaus_M]

Hello!

I dont't get the property value NI_ChannelLength and NI_DataType from a tdms file using the 'TDMS Get  Properties' vi.

All other properties are returned.

Inputs to  TDMS Get Properties: GroupName: RFbeam; ChannelName: Dev1/ai6.

Output: Variant on output 'property value' (wiring I64 to datatype input does not solve the problem. 

These properties are displayed in the TDMS File Viewer however. I marked the missing props with NOK:

 

What am I missing? Thanks for tips!

Klaus

Message Edited by Klaus M on 02-09-2010 10:56 AM

[Herbert Engels]

This is weird in that the TDMS File Viewer does exactly that ("TDMS Get Properties" wired with group and channel name, but no property name or type). You might want to look at the "File Contents: Value Change" event in "TDMS - File Viewer.vi" and double-check that your code does the same thing.

Herbert

[Klaus_M]

Thanks Herbert

For readers having similar problems, here are my experiences:

It works either without wiring a property name and datatype, as you mentionned before.

Resulting is a variant array. Result see attached solutionVariant.jpg

It also works wiring the right datatype as in the TDMS File Viewer and your first explanations:

Resulting is the channel length as Integer I64 or U64. Datatype constant representation and indicator representation must match!

See attached solution.jpg

My error has been wiring a string "I64" as datatype and a string indicator as value indicator. So stupid...

Regards

Klaus

[Herbert Engels]

You can wire any data type that LabVIEW can automatically coerce the value to. In this case, that would be any numeric data type (obviously, the range of potential values for I8 or U8 might be too small). Coercion between numerics and strings cannot be done.

Herbert