NI USB 6501 + Labview time resolution

[Luke_Trowbridge]

I'm looking to drive a relay (not directly) with the NI USB 6501 24 ch. board and LabView, and was wondering what timing accuracy can be expected.  The goal is to drive the relay for 100ms, but how close to 100ms will this setup be able to achieve?  150ms?  110ms?  Thank you for your input,

Luke Trowbridge

Goodrich De-icing and Specialty Systems

[Laura F.]

Hello Luke,

As seen in this benchmark KnowledgeBase for the USB-6501, the average time to update a digital output line is about 1 ms.  Running LabVIEW on a Windows machine, you can generally get a time resolution of 1-2 ms.  So my guess is that you can get fairly close to 100 ms, but it will be highly system-dependent.

Hope this helps,

Laura

[grahamwebb]

Hi Laura,

As high as 1-2ms? I'm trying to generate a PWM for a servo motor (1-2 ms on time every 20 ms), but the output is jumping around 1 to 6 ms. 😞  

[johnsold]

Laura has not logged in for over a year.

If you look carefully at the document she linked, you will see that it only reports averages over 10000 updates. With any software-timed device the timing jitter is very dependent on the behavior of the operating system. So while the average may be near 1 ms, that may simply mean that 9999 of the updates were very fast while one took most of 10 seconds.

To do PWM effectively you need a hardware timed DO or a real-time OS.

Lynn