08-31-2007 12:33 PM
@proud NI engineer wrote:
I am not sure why you are seeing extra samples, but using an N-Sample acquisition mode is probably not what you want since there will be gaps in the data. N-Sample mode re-arms the device each iteration (2048 samples in your case) and while it is doing this, samples will be lost.
Try setting your acquisition mode to be Continuous and see what happens. You might also want to set the number of samples to be a multiple of the rate so you can get an even 100 seconds of data.
Also, you can try using the logging featues of SignalExpress instead of the Save To ASCII Step. Recording the data using the logging features provides the following features:
1. You can use a Stop Condition for the Recording Options Tab to specify that the data should be logged for 100 seconds.
2. Once the data is logged you can view the entire log on the data view.
3. You can analyze the logged data using the built-in playback mode and any of the built-in analysis.
4. And if you are not using logging because you desire ASCII logs, you can enable automatic ASCII file generation by selection Tools>>Options from the menu. Select the Logging Category on the left and enable the Automatically Export Log to ASCII option.
Please let me know if you need further assistance.
08-31-2007 12:39 PM
The size of the gap in the data is very device / computer dependent. If you log the N-Sample data using the built-in logging and not save to ASCII you will be able to see the gaps if you view the entire log on the data view. Drag the logged data onto the data viewer and the gaps in the data will show up as empty spaces. SignalExpress accurately logs the start time of each chunk of data and displays the chunks with the correct spacing on the graph.
N-Sample logging / Save To ASCII will not buffer the data and fill in the gaps since the HW Device did not acquire the data in the gaps.
08-31-2007 12:43 PM
09-05-2007 01:16 PM
09-05-2007 08:32 PM
09-06-2007 09:25 AM
09-06-2007 10:05 AM
AC Voltage and Dynamic strain definitely use continuous.
If you just measuring a DC Level or a "Static" strain, then 1 Sample is fine.
02-09-2016 03:09 PM
Is there any way to coerce signal express to log data at a rate smaller than 1612.9 Hz or dt=620u while using all four channels of NI9237. I need to collect data over several hours and cannot handle such large data sets.
Thanks
02-09-2016 05:13 PM
I think you would've been fine starting your own thread.
The 9237 has a minimum sample rate of 1.613kS/s, so regardless if you set a rate slower than that the hardware will default to 1.613kS.
This is true even if you have other modules that can sample slower. The 9237 sample rate properties will take priority and upsample everything else.
I recall a similar question being posted a while back and the solution was to down sample using the Subset and Resample step IIRC.