Event Triggering and Data Storage

[JackT92]

I have 2 lasers that I am using as a method to measure velocity. When the velocity flag passes through the channel it blocks the first laser and then the second. From there I need to find out the time difference to then back out a velocity. 

Because I am new to LabView and don't have an encyclopedic knowledge of all the functions an VIs this task is proving to be extremely difficult. I have spent 8+ hours reading through the functions and VI pallets but can't seem to find any set of functions that will work together to do this task. 

My major issue seems to be converting the data types from the read VI to something that can be processed by the other VI functions. The uploaded VI is the most recent and seemingly closest that I have gotten. I have also tried putting the data acquisition on a loop that builds an array but am unable to both write to and read from the array. I have also gone through the various triggering pallets but can't seem to find one that will work with the dynamic or waveform datatype that I am reading. 

At this point I am basically still at square one and any help would be appreciated.

Thanks,

Jack

[Bob_Schor]

Light moves very fast, so you need something that can measure a very very short time.  Many years ago, I was present when Admiral Grace Hopper gave a talk that she opened by passing out 30 cm pieces of wire and noting that this was 1 nano-second (she was talking about the need for planning wire lengths for really fast computers).  So you'd need an A/D converter running at 1GHz (pretty fast!) to give you an edge detection with a 1 foot precision.  Better find another method ...

Bob Schor

[paul_cardinale]

---

@Bob_Schor wrote:

Light moves very fast, so you need something that can measure a very very short time.  Many years ago, I was present when Admiral Grace Hopper gave a talk that she opened by passing out 30 cm pieces of wire and noting that this was 1 nano-second (she was talking about the need for planning wire lengths for really fast computers).  So you'd need an A/D converter running at 1GHz (pretty fast!) to give you an edge detection with a 1 foot precision.  Better find another method ...

Bob Schor

---

He's not trying to measure the speed of light*.  He's using interruption of light beams to measure the speed of an object.

* The speed of light generally isn't measured anymore.  It's a defined constant with the value of 299,792,458 m/s.

[Bob_Schor]

Valid point, my stupidity.  It's the speed of the object, but the principle of estimating the delta-t by taking distance-between-sensors divided by estimated-speed-of-object (e.g. 1 meter / 100 m/sec = 0.010 s = 10 ms) and then sampling at a fast enough rate to get a sufficiently-precise estimate of the speed.

Bob Schor

[crossrulz]

What hardware are you using?  This would be easier to do with a simple 2 gate counter.