Voltage readings with 6034E card and CB-68LP board

[Gorman]

Neil,

I figured out what step I was missing and now understand it.  There is one more thing that I was hoping to do that I can't figure out.  I have the data coming out of the Sample Compression express Vi and it splits and goes into a chart and into a Write LabVIEW Measurement File.  They both work fine.  What I want to do is add another chart and have it display only one specific channel.  I am reading from 5 channels and because of the scaling difference I can't see the detail of one that I want.  I have tried to stack the plots but that doesn't seem to work. It just plots them as they normally would be plotted.  Is there a way to pick one channel out of the outputted data?

Thank you again for the help

William Gorman

[Neil_S.]

William,

To select a specific signal from a set of signals you can use the Select Signals Express VI.  This VI lets you specific signals from your acquisition.  You can then wire the output of this VI to another graph or chart to show only the data that you selected.  Let me know if you have further questions.

Regards,

Neil S.
Applications Engineer
National Instruments.

[Gorman]

Well I have another question and since this has been a helpful place I shall try it again.  Attached should be a screen shot of the vi that I am using.  With the rate, number of samples  and reduction factor all the same quantity ie. 1000, I record one sample every second and that is how it is saved.  Now to save 1 sample every 5 seconds I simply changed the rate and number of samples to 200 and left the reduction factor at 1000.  This displayed the data on the chart once every 5 seconds however when I go to the saved file it is saved such that it collected every second but each 5 second interval has the same number.  Meaning 1-5 seconds was some number A, 6-10 seconds was some number B, 11-15 seconds was some number C, etc.  I worked on this earlier on my own and thought that if I kept the rate and number of samples the same that this problem would not occur.  I am trying to have so that it saves every 5 second iteration and not the numbers inbetween.  The farther apart the rate and number of samples are the longer it takes for the Saved File As prompt to show and that is another reason I wanted to keep those numbers the same.  Any help would be great.

Thank you

William Gorman

[SimonH]

William,

The reason your saved data contains a lot of repeated data is that while the Reduction VI outputs data on every iteration it can only output valid data on every fifth iteration.  The reason for this is each loop iteration provides it with 200 new data points.  With a reduction factor of 1000 it needs 1000 new data points to produce 1 data point as output.  Thus for 4 out of 5 loop iterations it is merely outputing the stale compressed data point as it waits for enough data to calculate a new compressed data point.

If you only want LabVIEW to save the valid data points wire the Data Valid output of the Sample Compression VI to the Enable input of the Write to Measurement File VI like so:



I hope this helps.

Regards,

Simon H
Applications Engineer
National Instruments
http://www.ni.com/support/

Message Edited by Simon H on 02-01-2007 02:11 AM

[Gorman]

Thank you Simon.  That did solve the issue that I was having with saving the data.  However, now there is no File Save As prompt.  Instead it just saves to whatever is typed into the File Name which is located in Properties of the Write LabVIEW Measurement File.  Whereas before it would show the Save As prompt and be opened to the folder that was typed into the File Name.  I got around this by adding a terminal to the Write LabVIEW Measurement File which just gave me a control on the Front Panel that I can type the file name into.  I didn't know if this was supposed to happen so I am just making someone aware that it did happen.

William Gorman