08-28-2007 03:12 PM
08-29-2007 05:37 PM
08-30-2007 10:32 PM
08-31-2007 04:00 AM
Hi,
In DAQ Devices, the number of records or samples taken on each data acquisition is determined by the sample rate and the number of samples to be taken. I have not used the scope toolkit before but i noticed there is a "niScope configure horizontal timing.vi" under the configuration sub pallette. with this vi it appears you can dictate the number of sample and the sample rate for which you wish to acquire. As i say i have no working knowledge of the Scope drivers but that might be the place to have a look.
Craig
09-06-2007 11:29 AM
09-07-2007 01:31 AM
Matt,
After playing with the code for a while today, I realize that the introduced delay in the loop causes some of the data to be lost. I found that out by changing the the input voltage. I noticed that the loop keeps fetching old data without updating the samples. I simply want to acquire data once a sec and then save that once a sec. what are we missing here? Please help!
Thanks!
09-07-2007 05:22 PM
09-10-2007 12:54 PM
Hello Matt,
Thanks for your note! The issue is still there! When I set up the sample rate and points per fetch to 1, I expect for the digitizer to read the voltage once per sec and record that value once per second. Instead I see a very large number of values being stored and I'm not sure why that happens!! Also, with the mentioned setting, I read dt to be .000655!! I expect that to be 1 Sec.
It seems that there is no correlation between sampling rate, dt, and saved data. Please let me know what is going on!!!!
Thakns.
09-10-2007 01:38 PM
09-11-2007 06:29 PM - edited 09-11-2007 06:29 PM
Hi New_Programmer,
I would encourage looking at some of the LabVIEW shipping examples for NI-SCOPE (Help >> Find Examples… >> Hardware Input and Output >> NI-SCOPE), and the NI High Speed Digitizers Help (Start >> Programs >> National Instruments >> NI-SCOPE >> Documentation). These resources will help show and explain how to learn the scope functions. The following DevZone document will also help explain about vertical and horizontal configurations: Getting Started with NI-SCOPE.
The reason that your dt is .000655 is that the 5122 has a minimum sample rate of 1.526KS/s (5122 Specifications, p13), and 1/1526 = .000655. Through the examples, you will find VI’s and property nodes which allow you to query what the scope is doing (actual sample rate, samples per record, etc).
I would like to ask for an overall summary of your application. I understand that you want to essentially stream data for 3 hours, but how many channels will you be using? How fast will you be running? What memory option does your 5122 have (8MB, 32MB, or 256MB)? Etc.
In your very first post, you mentioned that you would not have enough memory. I believe that memory will not be a problem, depending on what rate you are sampling at. If you sample at slower rates as mentioned previously, pulling memory off of the 5122 and saving it to disk will not be a problem and the 5122 on-board memory will not overflow because the PXI bus can handle up to ~110MB/s of data.
Do you have any regular DAQ cards available to use for this
application? Based on this project described throughout the forum (wanting
to acquire 1S/s and record this value), I believe a DAQ card would be better
suited for your application. I would suggest one of our M-series cards (USB,
PCI, or PXI).
Message Edited by David L. on 09-11-2007 06:30 PM