Limit Step - Timestamp off limits

[StephenRobertson]

Hello,

I've acquired some data from a Tektronix DPO3034 scope using labview SignalExpress 2011 5.0.0.  

The data is a set of 4 waverforms each 100seconds long captured each time the scope triggered.  It was running overnight so I will have somewhere in the region of 500 captures.

What I am trying to do is analyse one of the channels using a limit test to see if any of the waveforms fall outisde expected limits.

The attached image shows the waveform and error I am getting

The details are

"Error occurred in Limit Test step.

The specified time stamp is after the end of the limit."

If I try a user defined constant as the limit then it seems happier but what I want to do is put a tolerance on the waveform that is shown in the image.

Any suggestions?

Thanks

Stephen

[RER]

Hey Stephen,

Do you want the good new or the bad news first? Bad news, right? Always start with the bad news!

Bad News...

Although I had never used the "Limit Test" step before, I have just been played around with Signal Express and managed to replicate the issue you saw (The specified time stamp is after the end of the limit). 

Good News...

I have worked out how to resolve the issue. When the Limit Test Step is configured to work with "User Defined Signals" is requires the data to be forematted in a particular way. Specifically, it seems to require the default header that is applied when saving an LVM file.

For my test application, I dropped down a "Load from ASCII" step, which read some noisey sinusoidal data from disk.

I then place down a "Limit Test" Step, configured to work with User Defined Signals, Between Limits and Signal Limit and Range. I point this step at a limit file that contains a clean sine wave. This file also includes the default LVM header information. This allowed the limits to be loaded correctly, as you can see in the following screen capture.

I have attached zip file, which contains 2 .lvm files I used here; one contains the data (noisey sine wave, with a time column) the other conatins the limit information (header, plus clean sine wave).

I hope this has been useful Stephen.

Best wishes with the rest of your application developement.