Data Translation DT9857E variable IO latency

Hi,

I'm using DT9857E with 1 OUT (sig gen) and 2 IN (IEPE Mics) channels to capture data into MATLAB - I am using the DT hardware Toolbox.

I have found that the system I/O latency changes from measuement to measurement making it difficult to use multiple repeats of the same measurement for data processing, as the signals are not synchronous between measurements.

I used implementation of background as well as foreground measurements from the DAQ toolbox and the result is the same - variable system latency.

I checked that by creating a loopback channel from OUT0 to another channel (IN3) and run 3 separate measurements. Then computed delay between measurements using finddelay MATLAB function. Each measurement is shifted between one another by a different (unpredictable) number of samples.

Is there any fix for that, or should I always run a finddely function and then adjust the signals so they are in sync ?

Appreciate any help,

Karol

Answer 1

[Pratyush]

Hi Karol,

To address variable system latency in data acquisition with the DT9857E device in MATLAB, you can try the following approaches:

• Use hardware timestamps if available to align data precisely.
• Implement continuous streaming to avoid starting/stopping latency.
• Employ hardware triggering to synchronize input and output channels.
• Utilize dedicated synchronization lines for clock alignment.
• Pre-fill the output buffer to minimize initial latency.
• Ensure consistent sampling rates and use the hardware clock for timing.
• If hardware solutions fail, use software compensation with functions like "finddelay" to align signals post-acquisition, automating this process in MATLAB if necessary.

Hope this helps.

[Karol Bugaj]

Thank you, I will try different approaches. So far finddelay works OK, but is not optimal :)