Threshold detector vi?

[Mark Mutton]

Is there a vi that detects threshold as aposed to peak. My application has two wavelets produced by echo's from the interior of a gun barrel. These waves change in amplitude therefore the peak detection doesn't work becase the threshold setting must be variable. I belive that a threshold detector vi would do the trick.

Thanks a ton

Mark

[Dennis_Knutson]

I'm not sure exactly what you're looking for since Waveform Peak Detection has a threshold input but there's also the Basic Trigger Level Detection function right next to it on the palette.

[Mark Mutton]

My application hase two echos that vary in time and amplitude. I need to find the exact posistion of the first part of both waves and find the time difference between them. The peak detection vi doesn't work becase the wave varies in amplitue. If i could find the posistion of the threshold of the wave i could determine the delta T. I have attached a pic of an example wave. I need to find the exact start position of both wavelets.

[Dennis_Knutson]

Well, I would use the Trigger Level Detection. You can modify it to return all trigger locations. On the diagram, there's an Index Array function that returns element 0. The input array is all locations that have met the trigger condition. If you create an array of the relative time of all locations, then you can index out elements 0 and 5 (for example) and subtract the two to get a time difference.

Also, please don't post .bmp files in the future. They are way too big and take a long to to view. Use Paint to save as a jpg or png file

[Mark Mutton]

Thanks a lot. This looks like exactly what i need, however, i am new at labview and am not sure how to make the output an array.  In other words i get the first trigger location, but i dont know how to set up the sub vi to output an array of triggers.

[Mark Mutton]

Ok i see what you are talking about now.  Last question i swear. How do i make the array an output of the sub vi?

[Dennis_Knutson]

Here's the VI I use (and a picture of it as well). To add an indicator to the connector pane, right click on the icon and select Show Connector. With the wiring tool, click on an empty terminal and then click the indicator. Be sure to save the modified VI as a new name and in a new location.

Message Edited by Dennis Knutson on 09-16-2005 11:28 AM

[Mark Mutton]

Dennis, Thanks for all the great help!!!