Log from Digitizer

[Randy36]

I need to log both channels of my digitizer for 8 seconds.

I need to see how 2 waveforms (both at 350kHz) are changing overtime so sampling rate needs to be as high as possible. 

Nothing fancy needs to be done. 

No triggering. No timing. No special file type. Files don't even need to be indexed. 

Just click. Log. Save the file manually. 

What is the most simplistic way to do this?

We have a bunch of NI software (Labview, Signal Express, ect..), but nobody on the team knows how to use them...

Thank you very much!

Randy

[Leah-L]

Hey Randy,

The simplest way to acquire data from a digitizer and save to a file is to use the Scope Soft Front Panel. This will not require any experience programming in LabVIEW. 

To open the Soft Front Panel, go to Programs>>National Instruments>>NI-SCOPE>>SCOPE Soft Front Panel. 

From here, you can configure your acquisition with or without triggering. You can run your test and Pause it when you are done aquiring. Once you have done this, go to File>>Save Data. I would recommend saving the data as an lvm file. An lvm file is a tab-delimited text file, which you can easily parse into a spreadsheet file. 

Hopefully this helps!

[Randy36]

Hello Leah, 

I'm very sorry for my delayed response I was waiting for an email but I never recieved anything. 

Yes, I tried this technique but the problem is that the data it saves seems to only be as large as the window size in the scope's viewer?

Am I misstaken?

I need to log about 10 seconds worth of data then save the file. 

Other then not being able to log for as long as I need to, this method is perfect. 

Please correct me if I'm misstaken or you have a better solution.

Kindly,

Randy

[Leah-L]

Hey Randy36,

You are probably right about the soft front panel only saving the data that can be seen in the scope window. 

I would recommend looking through some of the example programs that come with the NI Scope driver. To do this, open LabVIEW and go to Help>>Find Examples. Then Expand the folder that says Hardware Input and Ouput>>Modular Instruments>>NI-SCOPE>>General. In that folder, you will find an example called NIScope EX Save to File. Try running this example and see how it goes!

[DFGray]

The amount of data the NI-SCOPE Soft Front Panel can save is limited by the amount of data your scope can take in a single acquisition.  This will depend upon how much memory your scope has and the native bit depth of the acquisition (e.g. a 5122 takes 16-bit data).  You can change the record length in the SFP by choosing Edit»Device Configuration and selecting the Horizontal tab.  You may get where you need to be by just doing this.

However, you can get far more data and higher data rates if you stream from the device directly to disk.  This operation will be limited by your bus and disk speeds.  Typical sustainable values are around 20MBytes/sec - 40MBytes/sec, although with RAID systems and PCIe busses, this can get into the hundreds of megabytes per second.  To do this, you need to set your scope up so you are fetching from it as you are taking data.  A simple example can be found in niScope EX Fetch Forever.vi, in the NI-SCOPE examples.  However, this does not save data, it just fetches it.  After you fetch the data, you need to save it, preferably in a different thread than the fetch code.  This is easy in LabVIEW - use another loop.  You can find an example of this in niScope EX Save to File - HWS Low Level - Single Channel Stream.vi.  It uses NI-HWS, but the calls to NI-HWS could easily be replaced with either the binary primitives or TDMS calls.  This example fetches like the first one, but uses a queue to send to data to another loop, where it is stored in a file in a parallel thread.  Note that displaying your data will slow down your maximum acquisition rate, so the example does not do this.

Good luck!  Let us know if you need more help.

[Randy36 · Accepted solution]

Yes, I found device configuration option and that solved my original issue (sort of).

But these files are giant and difficult to deal with.

I found a MUCH easier solution - SignalExpress.

In my case, the end goal is to measure the real power output of an electrosurgical generator.

Logging the RMS values for both digitizer channels is more useful then the waveforms themselves.

SignalExpress lets you do both quickly. Nothing complicated.

Next, I need to account for the signal conditioning (stepping the voltage down), I can then use SignalExpress to apply formulas to the RMS values.

Bottom Line for the Newbies like myself:

Expect to invest TONS of time figuring out NI's software and system.

Even for BASIC things like measuring and logging the voltage is a nightmare.

NI is really for people that are building incredibly complex systems.  

Here is my advice for anyone getting started:

1. Use the device's software NI gives you first to see if it can do what you need it to do.

2. Use SignalExpress to extend any functionallity you need.

3. Use LabVIEW if you need even more functionallity.