simplest way to log continuous data NI USB-6251, Signal Express 2.5 LE

[wanfaz]

Hi,

I'm out of time. I thought this would be a quick and easy task but I am stuck...

I have in my hands  NI USB-6251 with Signal Express Limited Edition 2.5.

I was told this could be done with no hassle and programming required.

I hope this won't go  way beyond what I was prepared to do.

The task is simple: I need to log in data from 4 different channels at a slow rate. Initially maybe at 10 readings persecond, then one reading per second, for maybe a few hours.

Can this be done? What about the buffer size? I tried using the recommended values but there must be something that I am just not getting.

Please help. Any advice is appreciated.

Thank you.

[Speedy_Badger]

Hello wanfaz,

The only limitations that Signal Express Limited should impose on you is that only a single log file can be recorded and loaded at once and some of the additional signal processing and analysis steps are not available. There should be no limitation on the length of time you are able to acquire for. That being said, can you be more specific about what is going wrong?

What exactly is occurring?

You asked about the buffer size. Are you receiving an error?

Are you acquiring analog or digital data?

Is your acquisition continuous or finite?
 
With more information we can try to get you back on your feet!

Regards,

[wanfaz]

Hi Chris, your reply is music to my ears... 🙂

The signal is analog for the mean time, acquisition is continuous.

I received an error that I think is solved by me setting the timing settings for timeout to -1.

I have also changed the settings for 'Data' under Tools>Options for exporting data to -1 for unlimited size data transfer.

I had initially thought it was the buffer size. It seems that the buffer size works well enough being left at the default value 100.

I am getting some data now but it stops after 15 min saying that I should perhaps not update viewing while data is being recorded.

How big a file can the logged data be? Is there a limit to that?

Thank you. Very much appreciated.

[G-Haad]

hello, similar issue as I'm using a NI usb 6008 and signalexpress 2.5.
I am trying to set my continuous sampling rate for an analog DC input to 1.67mHz (10 min) using a buffer (#of samples) of 2. my timeout is set to -1 but I get an error every time I try and log the data. When I go up to 10mHz, all seems well.

I have turned off my update SI feature through VIEW.
I have tried many iterations of turning ON/OFF features under my EDIT-Options-logging

this is what the error message keeps encouraging me to do.

still no go,  ...help

Ryan

[wanfaz]

This is the message I get : "Data Discontinuity Error: SignalExpress cannot continuously record with the requested sample rate. You can try and reduce the sample rate of the data acquisition step. To allow SignalExpress to record signals at a faster rate you can uncheck the "Update Signals Views while Running" in the View menu or set the "Prepare log data for viewing" logging option to "After logging complete"."

I have done all recommended but still get the error message.

My settings is continuous, samples to read 100, sample rate 10 Hz, timeout set to -1. I took the measurements for 30min, so I have around 18,500 data values. But some how now I am not too worried because I can still view and log the data and export to Excel. (So what is the error all about?). I need to take measurements for a full day, I hope this is possible.

[Speedy_Badger]

Hi wanfaz, Ryan,

You need to keep in mind the differences between the N Samples and Continuous sampling methods. When you use N Samples the Samples to Read entry corresponds to how man samples you want to read. When using Continuous sample however this value controls the size of your buffer. The Data Discontinuity Error usually occurs when you overwrite the buffer before you read the data. Can you give me some more detail on what is going on?

Specifically:

What is the actual DAQmx error that is thrown? The Data Discontinuity error is thrown by Signal Express, however there is usually a DAQmx error that leads to this. You can find this error by looking at the DAQmx step and seeing if there is an error present.

You mentioned in your first post that you were using recommended values for Samples to Read and Sample Rate. This is usually a 1:10 ratio respectively. In your latest post you say you are reading at 10 Hz and 100 samples. Which one are you actually using?

I am running a simple test as we speak with your settings and I will see if I can recreate the error.

Regards,

[G-Haad]

My error message is such:

"Error 200077
Measured registered value is not supported value for this property
Property: SampleClkRate
Requested: 1.67e-3
Valid value begins with: 5.587935e-3
Valid value ends with: 10e-3"

this was with a buffer of 100, a timeout of -1 and sample rate of 1.67mHz.

Ryan

[Speedy_Badger]

Hi Ryan,

The reason you are getting that error is because the sample rate, 1.67 mHz, is not supported by the USB-6008. The smallest sample rate supported by your device is 5.587935 mHz and the maximum sample rate is 10 KHz. The 200077 error displays this information for you and is a good guide for finding out what your device supports. Another excellent reference is the specification or user manual for the device.

Hope that helps!

Regards,

[wanfaz]

Chris,
I set the sample rate at 10 Hz and I left the "samples to read" entry (which is the buffer size since it's continuous) at the default value shown in the box which is 100.

But even though the Data Discontinuity Error is shown, data logging seems to be fine. So I am wondering what the implications of the error is.

The lab is closed for the weekend. I will run it again on Monday to see if any DAQmx error was issued along with the Data Discontinuity error. I did not notice any DAQmx error with that setup earlier.

Thanks for the time Chris.

[Speedy_Badger]

Hi wanfaz,

I am glad you are able to record the data and use it afterwards, however I am still curious about the data continuity error you were receiving. Were you able to recreate this behavior after the weekend? Was there a related DAQ error that went along with it?

From the sounds of it I believe what you are seeing is actually a Data Continuity warning, rather than an error. When you look at your data, are you able to see continuous information for the entire range? Are there any points in time that show discontinuity?

If you have the time, lets see if we can get some more detail about the error and perhaps find a way to eliminate it.

Regards,