How to insert, as an input variable within formula, the total time window on scope?

[mander]

How to insert, as an input variable within formula, the total time window on scope (i.e. 20ms/div x 10 div = 200ms)?

BELOW IS AN EXAMPLE OF ISSUE:

FORMULA FOR ACTION INTEGRAL:

STATISTICS:

Input variable: DPO4034(CH1);

Check Box: number of samples.

FORMULA

Input variable 0: DPO4034(CH1); alias: x0

Input variable 1: "Total Time Window on Scope???"; alias: x1

Input variable 2: Number of Samples (CH1); alias: x2

Under Operation Setup: Formula

Y= (x0^2)*(x1/x2)

Output: Processed Data 1 (CH1)

THEN USING STATISTICS:

Input signal: Processed Data 1 (CH1)

Check Box: SUM

Output: CH1 Action Integral [A^2s]

[Catherine-B]

Hi mander,

The total time window on the scope cannot be directly input into a formula as a variable. You will need to go through an intermediate step and use the number of samples and the sampling rate to calculate the time window and then input that result into your formula.

Regards,  

[mander]

Dear Catherine B.

First of all, thank you for taking time to help.

However, how do I retrieve the "Sampling Rate" from scope? The "Number of Samples" is retrieved within the "Add Step - Statistics". Is there another "Add Step"  that will retrieve "Sampling Rate" information?

Sincerely,

Michael

[Catherine-B]

Hi Michael, 

I have not been able to locate a step that will allow you to retrieve the sampling rate information. You may have to hard code it in your formula based on the sampling rate you used when setting up your data acquisition. There does not appear to be a way to progromatically retrieve this information in SignalExpress. 

Another option you may find useful is the "Measurement duration" information under the Statistics Step. Some additional information about this statistic can be found at the links below. This statisc does not appear to be available in all versions of SignalExpress, however, so may or may not be an option for you. 

http://zone.ni.com/reference/en-XX/help/371268P-01/msureasstvi/statistics_se/

http://forums.ni.com/t5/SignalExpress/SignalExpress-Statistics-Measurement-Duration/td-p/1590140 

Best, 

[mander]

Hello again Catherine,

Hard coding sampling rate is not an option since end product will be used by another customer. I was able to create a work-around (although definitely not ideal) by retrieving the "Burst Width" from a channel on the scope that isn't presently being used for "real" signals. If I set trigger to occur at left most side of scope window, then the burst width is the total time window and therefore I can calculate required sampling rate by divding the retrieved burst width by the retreived number of samples for any user defined scope window (i.e. time scale). However, I unfortunately will lose that channel for other more useful signals. I am surprised SignalExpress is not able to retrieve sampling rate or time/division . . .

Sincerely,

Michael

[Catherine-B]

Hi Michael,

I’m glad you were able to getting it working!

I understand that having to use a work around is not ideal. While SignalExpress has some very powerful capabilities, there are some limitations on the options that are available. If you want to do a fair amount of processing or build more complex formulas, LabVIEW may be a better fit for your application as it allows for access to far more options and parameters.

Regards,  

[mander]

Hi again Catherine,

I have now added another TekScope (TDS3032B) along with the DPO4034 and run the same work-around on the TDS3032B using CH1 as the "real" signal channel and CH2 as the "burst width" channel. However, the value returned for CH2 is nominally 99E+36 (min 99E+36, max 99E+36) with very few retrievals of correct burst width (~200ms). Seems the SignalExpress program is unable to consistently retrieve from TDS3032B the actual burst width (scope's time scale/window) and defaults to 99E+36 value. Any ideas on what is occurring and how to make it work? Attached are some screen captures to help guide discussion.

Regards,

Michael

[mander]

Catherine,

Not sure why, but if I set the channels being used for "burst width" to 50 Ohm input impedance (though this channel has no connection with outside world) within SignalExpress program, the burst width value retrieved again becomes the total time scale window . . . Work-arounds on top of work-arounds . . .

Regards,

Michael

[mander]

Catherine or anyone with a solution,

Unfortunately, I am still having issues with TDS3032 grabbing burst width. Attached are the "burst width" graphs for both DPO4034 and TDS3032 (Note: I have also tried a TDS3034 model with same problem). Seems SignalExpress does not consistenly grab burst width of TDS3032/3034 channels and therefore registers their default "max" value of 99E+36. Question: is this a problem with NI SignalExpress software or Tektronix scope models? If scope model is to blame, then we can simply order only the DPO4034 models . . . However, if it is software related, we need a reliable solution. Also, when starting up SignalExpress software (with scopes already connected and all channels on), SignalExpress sometimes does not register all scope channels and therefore corrupts formulas. Any ideas?

Regards,

Michael

[mander]

attached are the "burst width" graphs