6024E minimum sample rate

[daveyK]

Hello,

I have a PCMCIA 6024E card  running LABView 7.1.  All I'm trying to do is log five voltages simultaniously over five minutes.  When I set the sample rate to anything less than 60Hz it won't display data in my graph...and anything over 60Hz the data looks bad (in a graph).  All I really need is a sample rate of like 6Hz.  Actually it would even be better if I can get the values of each channel into a file and I can just create a graph in Excel later because I've been screwing around with this for a day now and I can't make it look good.

I have the Acquisition mode set to continuous and everything is in a loop.  Then I just press run instead of continuous run.  Is this the correct way?

If anyone can tell me how I can get sample points from five channels for five minutes at like 6Hz that would be wonderful.

Thanks for your time,
Dave

Message Edited by daveyK on 01-05-2007 09:40 AM

[Dennis_Knutson]

When you change the sample rate to 6 Hz, do you also change the number of samples? If you leave it at 100 samples, your chart will update every 16.66 seconds (100/6) but it will update. Try setting the number of samples to something closer to the sample rate. For example, if you set the number of samples to 6, then you will get the entire scan and the chart will update once a second.

[daveyK]

I changed it to 2 samples at a rate of 6Hz and nothing is happening on the graph. 

PS.  If I just keep the ribbon cable dangling there from the card I should still see some data right?

Thanks,
Dave.

[Dennis_Knutson]

Looking at the chart in the VI you posted, you have auto-scaling turned off. Turn it back on and see if data is plotted with your cable disconnected.

[daveyK]

Thank you very much for helping me!!!

In my most recent VI I do have auto scaling on. 

Ok it works if I change it to like 100 samples at 200Hz.  10S@60Hz seems to be very clean.  It does not work at like 5S@20Hz. 

Why does the time on the graph automatically change to 3G on both extremes with or without autoscaling?

Ok last question....I think I will just log the data points into a spreadsheet and create a graph in excel.   I posted an example picture of the vi.  When I run it it asks to open a file so I click on an excel file I created and then it asks me to do it again continuously.  If you can point me in the right direction that would be great.

Thanks,
Dave

Message Edited by daveyK on 01-05-2007 11:29 AM

[daveyK]

I looked in the spreadsheet and there is a data point in there so I just have to have it append.  It prompts me to open a file each time a new data point is made.  So...how do I just keep it writing?

Thanks,
Dave

EDIT:  I set append to true and it's working but it's still prompting me to what file to write to every ddata point.

Message Edited by daveyK on 01-05-2007 11:40 AM

[Dennis_Knutson]

You have set the format on the x axis to SI notation. You can set it to absolute time if you want the actual time to be displayed.

Look at the VI you are using to write the file. Do you see the input called 'append to file? (new file:F)'? That means that the default for this is False and that you will get a new file each time. Wire a True to it to append.

Do you see the input called 'file path (dialog if empty)'? Since you have nothing wired to it, the path is empty and you get a dialog each time. You can place a file path constant on your block diagram so that you can specify a file before you run the program or you can have the dialog and use a shift register wired from the new path output back to the path input.

[daveyK]

Thak you so much.  It's working.  Is there anyway I can have the data coming out with a timestamp to the spreadsheet?

Also I think that when I set it to lets say 2samples @ 6Hz it doesen't work because I have 5 channels.  Am I correct in thinking that I would need a minimum of 5 samples for it to work?

Thanks,
Dave

[Dennis_Knutson]

If you want the timestamp, the easiest thing for you to do is use the Write LabVIEW Measurement File function and don't convert the dynamic data to a 2D array. Just wire the dynamic data to the 'Signals' input.

The number of samples refers to number of samples per channel and the only minimum you have is 1 sample per channel. I'm running your VI in simulated mode and I have no problem plotting data with a 6 Hz rate and 2 samples.

[daveyK]

Alright something is up here.  I've tried it with the "Write Labview Measurement file" and "Write to spreadsheet file" and it only seems to log data if I set the rate to 21Hz or higher independent of the number of samples. 

You said earlier that if I set the samples to lets say 100@21Hz then it would log 1 sample about every four seconds? 

I have it set to 100Samples@21Hz and it's logging data at 21Hz or every .0476 seconds at 100Sample blocks.

So this is how it works...I can have it set to 19samples or 500samples and it only logs data if the rate is set to 21Hz or higher.  If I set it to less than 21Hz I can see the bubble moving down the wire but it's empty for some reason.

Any ideas?

Thanks,

Dave