time offset on x scale

[aartjan]

I use Labview to save waveforms to a TDMS file that I want to process in Diadem. Unfortunately, Diadem doesn't seem to recognize the timestamp in the waveform to properly scale and offset the time domain waveforms when viewing them. I fixed the issue of offset by writing the property "wf_start_offset" with the first timestamp. Still the x scale will not properly scale. The offset turnes up in a number, not in time.

Another approach is to make a full timestamp channel. What a waste.

Anybody have a suggestion on how to do this smarter?

[Brad_Turpin]

Hi Aart-Jan,

You have indeed found a chink in the LabVIEW-DIAdem Connectivity armor.  The root of the problem is that LabVIEW can handle explicit date-time values with up to something like femtosecond accuracy, since LabVIEW devotes 16 bytes to each date-time value.  DIAdem, however, only dedicates 8 bytes to each date-time value, resulting in an effective date-time resolution of 0.0001 seconds.  When DIAdem implemented waveform channels in DIAdem 10.0, R&D decided to categorically ignore the date-time content of waveform channels.  The "wf_start_offset" property does show up in DIAdem, but it is interpreted as LabVIEW intended-- as a numeric time shift.  This means that your waveform can start at -1.5 seconds for pretriggered data or at -10 degrees for angular data.

The absolute start date-time value of each waveform channel can be read out by a DIAdem VBScript-- but only to 0.0001 second resolution.  This absolute start date-time just doesn't show up visually in the Data Portal, and it is not used to plot curves in VIEW and REPORT.  Your options are therefore to create a separate date-time channel in LabVIEW, which artificially inflates the size of the TDMS file, or to create a date-time channel in DIAdem after loading the TDMS file, which requires running a VBScript.  The good news there is that DIAdem 10.1 can have custom loading routines so that this could be made automatic for your TDMS files.  But either way you will need a separate date-time channel in DIAdem in order to view the data with the date-time information on the X axis of a graph, and in both cases that X axis will have a resolution limitation of 0.0001 seconds.

Ask if you want further information,
Brad Turpin
DIAdem Product Support Engineer
National Instruments

[greentea2]

Hi All,

I am having difficulty with the time scale (x axis) of data from a pressure sensor.  Due to noise, I have snipped a section of the waveform and now need to move the data from a certain time e.g. .4 seconds to start at 0 seconds. Note, I have two channels, one for the time in the following format:

02/30/2011 19:36:51.3521 & one for the pressure.  For the time format, the first is the date followed by ??? so am a bit confused on how I could possibly use offset correction or another function.

Thank you!

[ThiCop]

hello greentea, (BTW nice nickname)

This format stands contains:

- Date

- Time (hours:Minutes:seconds)

Does this answer your question?

[greentea2]

Thank you, Thierry. It's my favorite drink after coffee, of course.

My problem was with x axis offset correlation.  After much searching, I discovered that the time must be extracted from the channel because when imported into Diadem, time and voltage are coupled (more info can be found at http://digital.ni.com/public.nsf/allkb/C74C08AED367563E862576BF005A53E4?OpenDocument). 

Is there a current Diadem user's manual I can refer to? I found one but it's dated few years back.

[ThiCop]

Hello greentea,

One recent Manual you can refer to is for example this one:

http://www.ni.com/pdf/manuals/373082j.pdf

Also this webpage can be a good starting point to start to work with NI DIAdem:

http://www.ni.com/diadem/start-support/

Another useful page is this one:

http://zone.ni.com/reference/en-XX/help/370859J-01/

One other interesting thing might be the DIAdem Basics (http://sine.ni.com/tacs/app/overview/p/ap/of/id/1580/ol/nl/oc/nl/srcred/no/) and DIAdem Advanced (http://sine.ni.com/tacs/app/overview/p/ap/of/lang/en/ol/nl/oc/nl/pg/1/sn/n24:4127,n8:27/id/1579/srcr...) courses.

If there are other things you would like to know, then don't hesitate to let us know.

[greentea2]

Thank you! The information you provided has been extremely helpful.