PDA DAQ channels swapping

[Bandit]

Hi all, here's a further update.

The application as written by external contractor doesn't exhibit quite the same behaviour, but does exhibit data dropouts, that increase as sample frequency increases.

At 10Hz sample rate no drop out's occur.

At 40Hz sample rate over 20 seconds worth of data 1 dropout occurs.

At 100Hz sample rate over 20 seconds 14 or 15 dropout's occur.

By the time we get to 100Hz about 2/3 of the data is being lost.

I have tried hacking their code right back to just sample and write to file. At this point only 1 drop out occurs over 100Hz, but the channel switching occurs at that point.

I have tried a different DAQCard 6024E for if the first is faulty, but it exhibits the same behaviour.

I tried running the code on a laptop with the DAQCard installed, but found tweeks were needed to make the code run on the laptop instead of PDA. Once changes have been made to the code it's questionalble how valid running the same code on the Laptop is. I'm not even sure the DAQmx base drivers work on a laptop anyway.

I'm fast coming to the conclusion that either...

1. The card/PDA interface can't cope with shipping 6 channels of data at 100Hz as it comes in.

..or...

2. There's a bug somewhere in one of the LabVIEW PDA vis, or in the DAQmx base driver.

Can anyone advise if they have had something similar working (6 channels 100Hz or more logging to file). It doesn't seem very challenging to me.

Regards.

Bandit.

[StevenH]

Hi Bandit,

It sounds as if the data is being lost by the hardware as the driver is pulling the data back without causing an error.

For example, if the data being sampled is  1  2  3  1  2  3  1  2  3  where 1 is the data for the first channel, 2 is for the second channel and 3 is for the third channel, the driver is collecting the data and sorting it into channels as follows:

111

222

333

but in this case it seems that the data block is missing data points and is being collected as 1  2  3  2  3  1  2  3  1 so when the data is sorted it appears as though the channels have switched:

122

233

311

This could potentially be an issue with the expansion pod to which the DAQ card is connected, and so it may be worth contacting the manufacturer to see if they've come accross a similar issue.

Please let us know how you get on.

Best Regards,

Steve Harry

[Bandit]

Hi Steve,

Thanks for your input on this.

I think the fastest way is to draw their attention to this very thread - I'll do just that.

Regards,

Bandit

[buckidge]

I am having a similar problem with a USB6008 module, reading two differential analog signals, 500 samples on each at a rate of 5k/sec. It is also the case that reseting the aquisition seems to resolve the problem.

I'll going to try slowing aquistion (100 @ 1k/sec) to see if that helps.

[RER]

Dear Buckidge,

The best way to gain exposure to the whole online NI-community is to create a brand new thread.

As the posts shown here are related, I would certainly include a a link to this thread in your new post.

Once we see the new thread we will endevour to help you further.

Thanks for your time myfriend,

[Bandit]

Hi Buckidge,

I never got to the bottom of this issue. Combined with some other problems it was enough for us to abandon the project, and use of the PDA/mobile module. I hope you have better luck solving your issue. I'll search for a new post from you as suggested above, and watch with interest to see if you find a solution.

Best Regards,

Bandit.