System clock slows during data acquisition

[Butch]

In doing data acquisition using a DAQPad-MIO-16XE-50 (a parallel port device) I noticed that the system clock is losing time. I have a second independent clock that is displayed and recorded on video, which is how the discrepancy came to light. I am using LV6.0.2. This behavior happens on both Windows 98 and NT4.0. A delta of 5 minutes 14 seconds occurred in 3.5 hours. The resulting loss of sync between the data written to disk and the video is a problem. The experiment runs are from 7 to 15 hours long. There is also communication through the serial port that involves several wait statements to allow for the latency of some of the devices.
What is causing the apparent slowdown of the system clock? Is th
ere a fix?

[Doug (CapeFl)]

Consider using the Profile mode (under Project menu).
You can monitor all the VI's and see which vi(s) are using the most time. Use the snapshot feauture and compare the numbers every so often and see if they trend upwards with time. You may also want to check the Memory option, because you may notice a VI increasing its memory use, which may signify an unintitialized register, etc.
Good Luck, Doug

[Mark A. Hanning-Lee]

Butch wrote:
>
> In doing data acquisition using a DAQPad-MIO-16XE-50 (a parallel port
> device) I noticed that the system clock is losing time. I have a
> second independent clock that is displayed and recorded on video,
> which is how the discrepancy came to light. I am using LV6.0.2. This
> behavior happens on both Windows 98 and NT4.0. A delta of 5 minutes
> 14 seconds occurred in 3.5 hours. The resulting loss of sync between
> the data written to disk and the video is a problem. The experiment
> runs are from 7 to 15 hours long. There is also communication through
> the serial port that involves several wait statements to allow for the
> latency of some of the devices.
> What is causing the apparent slowdown of the system clock? Is there a
> fi
x?

A work-around: run a time sync program like Dimension 4,
www.thinkman.com . Make that program set your PC clock from the Internet
as often as needed.

Tip, it usually uses a machine name like wwvb.isi.edu.
You probably get less overhead if you use an IP address like
128.9.176.30, because then it doesn't have to do DNS.

BTW, Win2000 is much better in this respect.

Mark