Writing waveforms from Ch. 0 of niSCOPE to binary file in a multi-record setup?

Question

Hello,
I am not very experienced with niSCOPE and writing waveform records, so I need some expert help here.
Here is my application:
I am generating a pulse train using a 6602 counter/timer. Each rising edge of this pulse train triggers an niFGEN to generate a single sawtooth waveform output to another device and, at the same time, acquiring data from Ch. 0 of an niSCOPE. I am fetching one record per rising edge of the pulse train for the niSCOPE (multi-record setup).
The attached VI is where I am at thus far. All triggering and reading/fetching of the waveforms seems to be working just fine when testing with an oscilloscope. I now need to save each waveform record along with the timestamp of its rising edge trigger to a binary file. The bottom of the VI is where my attempt is at saving the waveforms to a binary file, so the attention should be there when looking at it.
I am running LabVIEW from a computer connected to the NI PXI-Chassis using a cross-over cable.
Questions:
1.) Do I need to convert the data coming in on Ch. 0 of the niSCOPE to digital? Does it come in as analog from an oscilloscope? If I need to do this, how can I accomplish this?
2.) When I try to run an example VI to write a waveform to a binary file by choosing "My Computer" in the bottom left of the VI window, it works it saves the file just fine. When I change this to run on "PXI2", a file is not even created and I get an error on File Dialog (code# 7, I think) each time the file is attempted to be closed. This may be a stupid question, but why can I not save data to a file on my computer if running the VI on "PXI2"?
3.) Assuming the saving of each waveform to a binary file is working (read: (2) is successfully addressed), how can I also write the timestamp of the starting trigger for the waveform along with the waveform in the binary file? An example VI of how I can accomplish this would be fantastic, but I haven't been able to find one thus far.
4.) When I was messing around and trying to accomplish this, it seemed that doing this writing may slow down the entire process too much. I need to record data to the extent of the sawtooth waveform generated by the niFGEN AWG for each trigger. Is there any changes I should make to my acquisition process in the niSCOPE section so that I can read each waveform, along with keeping the timestamp for each, and write this information to a binary file?
I need to get this working quickly, so any help on this is greatly appreciated. Thanks in advance.
Attachments:
5124_update.vi ‏157 KB

Answer 1

Thank you so much for your reply, David. Let me try and explain my
situation and setup a little better, as well as discuss the points you
made in your reply. Beware, you may want to refill your coffee as this
post is long .
I am using an embedded controller in a PXI-1044 chassis. I now have the
chassis hooked up to our local network, and I am deploying my project
to the chassis over the network as I am also connected to the local
network. I have an oscilloscope next to me that takes as input the
pulse train for a trigger and the generated sawtooth from the niFGEN
for each trigger (rising edge of the pulse train from the 6602
counter). Just to make sure synchronization is taking place, the
sawtooth is also fed as input to the niSCOPE for acquisition.
"PXI2" is what shows up when I choose to run a VI on the PXI chassis
rather than "My Computer"; not sure why the 2 is there either, but that
is what it says. I may have tracked down the issue I was having with
writing, but more about that a little later...
The attached VI is an update, although not much has changed. My
application design is like this (keep in mind that some values for VI's
are still constants in the block diagram while others are controls on
the front panel): I am using the 6602 to generate a 1 KHz pulse train
and routing this pulse train to PXI_Trigger0/RTSI0. I am also using the
PXI_Clock (10) as a sample clock for this, and also using this same
clock as the reference clock for both the 5422 and the 5124 (as per the
synchronization help file mentioned for synchronizing multiple
devices). Both the 5422 and the 5124 are triggered by a digital rising
edge (from the pulse train) on PXI_Trigger0/RTSI0 (as it was routed
there). For each trigger, the niFGEN generates a sawtooth waveform
using a stepped trigger mode and outputs it. For each trigger, the
niSCOPE acquires data. They are both synchronous, which is tough to see
since one has its trigger source on the front panel and the other has
its trigger source on the block diagram. All devices use PXI_Clock so
they are synchronized.
The expected behavior is to only generate a single sawtooth waveform
per trigger with a certain number of sample points. I want to acquire
the same number of samples using the niSCOPE, which is what I meant by
"the extent of the waveform" in my previous post. So, should I change
the 8192 to 1000 for the number of samples for the niSCOPE? What would
you recommend for the sampling rate? I have been using 5 MHz for the
niFGEN and 5 MHz for the niSCOPE...this is how it should be done,
correct? If it is different in the VI, please let me know. For some
reason, I have to adjust all of the values each time I open it since
the default values are not the ones I want.
I want to generate and acquire one waveform per trigger (one waveform
per record). However, I want to be able to record a large number of
records so I have enabled the circular buffer-like treatment of the
acquired waveforms. The 100 or 1000 records is actually just a number I
am giving it for now to make sure it is working before recording many
more records.
As for saving the niSCOPE data, I would like to save all data in a
single file that is NOT ascii (to save space). I have been looking at
the HWS file format, and would like to use it. I think the attached VI
includes this at the bottom of the while loop. For each trigger, I
would like to save the time (as accurate as possible) that the trigger
occurred for the record/waveform, which appears to be (absoluteInitialX
- relativeInitialX) as you said in your post (thanks!). I just need to
store as much information about the waveform and time information for
it as possible with the waveform in the file. So it looks like I will
need to use the wfm info for that information, providing portions of it
as waveform attributes in the HWS VI's?
What format of data do you recommend I fetch, and will I be fetching a
"Single waveform" or "Multiple waveforms"? Should I use I32, DBL, WDT,
or other for the format? A balance between good precision in values and
time it takes to fetch/record would be best.
Given all of the above, I am having one troube with saving data to a
file. As a reminder, I am deploying the project to the chassis over the
network. When I choose a location and/or file to save the HWS data to,
I only get choices that are on the PC's hard disk (such as C:\Documents
and Settings\cgifford\...) NOT the chassis's hard disk. When I choose
something other than "C:\" I get an error that the file could not be
opened. However, when I choose "C:\" everything goes fine. The saved
data is nowhere to be found on my PC though, so I am assuming that it
is being stored on the internal 60G hard disk in the chassis that must
be named "C" by default or something!?
I have been told by phone support that I should be able to make a
direct connection with the chassis just like another PC, and should be
able to access the information on its internal hard disk in a drag and
drop fashion. I however cannot directly connect to the PXI chassis to
get the data that has been saved on the hard disk. We are running
Windows XP on the PC. We did some poking around and noticed that the
chassis is not running Windows file sharing, and only has ftp and http
running. We tried to access it using ftp, but we didn't have a username
and password to supply it. So, how can we enable Windows file sharing
on the chassis? How can I connect to it to do drag and drop to get
saved waveform data off of it? This is the main problem I am now
facing. Eventually we would like to store data to an external hard disk
connected to the chassis, which assumes that I can have access to the
internal storage to tell it to save files to the external hard disk.
For now saving it to the internal hard disk is just fine until
everything is proven to work, but I would like to get the data off of
the internal hard drive to put on another computer.
Any answers/suggestions on my above questions are greatly appreciated.
I also want to thank you for reading this long post . I eagerly await
a reply. Thanks again in advance.
Chris
Attachments:
5124_update.vi ‏143 KB