wf_start_time accuracy

[MBoyd]

I have a quick questions regarding the wf_start_time property when writing a waveform from a DAQmx Read block to a tdms file.   I have a real-time computer connected to a PXI chassis performing some data acquisition.  I am using wf_start_time to line up data between analog inputs and a counter in post-processing.  I was wondering how accurate is the wf_start_time property?  Also, where is the wf_start_time applied to the signal (when the waveform is created? or when the data is captures on the DAQ board).  The analog inputs are collected at a 100kHz rate and the counter is updating as fast as possible (which is roughly 2-4ms).

I am looking for some user data, or actual usage experience, with wf_start_time other than the normal definition that I have found online. wf_start_time definition.

Thanks for any help.

-Michael

[Tim_W.]

Hi MegaWatts,

I haven't been able to find a lot of resources on wf_start_time, but did find a DevZone that references it:

How to Display Absolute Timestamps from a LabVIEW Waveform in DIAdem

Judging from the definition you referenced, I would guess that the value of wf_start_time might vary depending on if your DAQmx task is creating the waveform or reading it. I would still be interested to hear from members who have more firsthand experience with this property.

Tim Weilert

Applications Engineering

National Instruments

http://www.ni.com/support 

[MBoyd]

Thank you for the response.

I read the link in the previous post and it made me feel a little better about wf_start_time considering that NI was using it to calculate a timestamp based off the t0 and dt, though it doesn't completely give me warm fuzzies.  I would also like to hear someones first hand experience with wf_start_time and how accurate it truely is.