Can I prevent my Laptop Clock to shift during a continuous data acquisition ?

[Nicolas_Xenics]

Hello All,

I am developping a continuous acquisition software.
I use a 6062E PCMCIA card plugged into a DELL Laptop, Inspiron 5160, Pentium 4, 2.8GHz, 512MB , Windows XP, with Labview 7.0.

Number of channels acquired = 3, Scan Rate = 160KHZ (Internal Scan Clock).

Briefly, the block diagram is composed of 3 loops synchronized by Notifiers: Loop 1 contains a state machine which takes into account the main switches actions and intitializes the acquisition, Loop 2 realizes the acquisition and Loop 3 is dedicated to do the display.

When I run the software, I am able to do the acquisition and display the data with no problems; however I noticed that after a short period, the laptop clock starts to shift and I wanted to know if I could prevent this to happen; indeed, I need to retrieve the laptop clock time (As accurate as possible) to create the file names.


----------------------------------------------

Here are some observations after having recorded 37 files, 640MB per file.
NB: The names of the files are decomposed this way: MM-DD-YYY_HH-MM-SS


FILE NB: START: END TIME: DIFF:

1 1-11-2005_21-38-0 9.45pm 7 mins
2 1-11-2005_21-45-2 9.52pm 7 mins
--
--
5 1-11-2005_22-5-33 10.32pm 27 mins
--
--
14 1-11-2005_23-27-27 12.11am 44 mins
--
--
23 1-12-2005_1-6-31 1.50am 44 mins
--
--
32 1-12-2005_2-45-33 3.29am 44 mins
--

I noticed that most of the time, the difference between the Start time indicated in the file name and the End Time indicated in the Explorer was 7 mins, except for the files numbered 5, 14, 23 and 32 (Notice that always 9 files separate the first number from the second).

7 mins is actually wrong as well: I did a simulation using an external timer, and I saw that to create a file without using the display, it actually takes 11 mins and 7 secs. No difference when using the display option.

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Thanks for your feedback.
Nicolas

[AnujD]

Is this problem specefic to that particular laptop? Have you tried it on another laptop? Does it matter if the laptops are plugged in or not?

Regards,

[reddog]

If you're not using the DAQmx driver, I would recommend trying it with your application to see if it prevents your laptop from losing time. I believe this issue has been fixed or at least has been improved by the DAQmx driver. The root of the problem is that your DAQCard must use interrupts to transfer the acquired data to memory. If your data acquisition generates enough interrupts, it is possible that some system timer interrupts will be missed. This has the effect that your system clock gradually loses time.

[Nicolas_Xenics]

Thanks. I was thinking of this too but was not sure about it.
I will try with DAQMx.