12-29-2005 05:13 AM
12-29-2005 05:26 AM
Hi,
Are you saying that ur VI acquires DC signals but is not able to measure a 500Hz periodic signal?
Do keep in mind Nyquist Criteria while choosing sampling rate for measuring a signal of 500 Hz (When an analog signal is sampled at a rate more than twice that of its highest Frequency component, it can be properly reconstructed when reconverted back to the analog domain. The required sampling rate is called the Nyquist frequency.)
If you think this is not the source of your problem, plz post the VI you have developed so that we can suggest better
Regrads
Dev
12-30-2005 03:51 PM
Hi Jeferson,
I think that Devchander has a good point about the Nyquist frequency. I also noticed that you are only acquiring 4 samples/channel.
To obtain an accurate representation of a waveform, I recommend that you acquire at least 20 points per period of your signal. So, let us assume that you are sampling at 10,000 Hz (this will be a good frequency to use in your application as well): then you will need to acquire 20 samples/channel to obtain an accurate representation of the signal since 10,000/500 is 20.
I would also like to point out that there are some good shipping examples for triggered analog acquisiton. Go to Help >> Find Examples >> Hardware Input and Output >> DAQmx >> Analog Measurements >> Voltage.
01-02-2006 09:31 AM
01-03-2006 01:32 AM - edited 01-03-2006 01:32 AM
Hi Jeferson,
You have got the Continous acquisition coding wrong.
First of all, i suggest that you have a look at examples shipped with labview which perform continous buffered acquisition.
Also, have a look at attached VI.
I suggest you go with intermediate File write VI's instead of write to spreadsheet VI( this reduces overheads of opening a file and closing a file in each iteration).
In continous mode, the 'samples per channel' control in scan clock determines the buffer size.
see this link
http://digital.ni.com/public.nsf/websearch/E1E67695E76BA75B86256DB1004E9B07?OpenDocument
The number of samples per channle you want to read on each iteration ( 4 samples in your case), samples per channel( 12) do not seem to be optimal for the sampling rate you have chosen.
see if you can set these parameters : sampling rate, number of samples per channel to more optimal values.
regards
Dev
Message Edited by devchander on 01-03-2006 01:34 AM
01-03-2006 08:25 AM
01-03-2006 11:09 PM
01-05-2006 08:14 AM
Hi dev,
Thanks for the VI. It is working now!
Listen, now I am trying to send a signal to an anlog output, in a closed-loop system. However, I am having some troubles to send a calculated signal (from the inputs) to this output.
How would I program this part inside the vi you sent to me.
Thanks again.
Jeferson
01-10-2006 01:49 AM
Hi Jeferson,
Do you want to, Acquire voltage on analog input -> scale/modify it -> generate the scaled Voltage on analog output?
am i right?
Regards
Dev