Labview Data Analysis Program Help

[amcgl556]

Currently testing force outputs in model rocket engines.  I uploaded my constructed VI and one of my collected data sets....I'm having trouble rooting out the "noise" in computing my burn times displayed in my burn time array.  The burn times should be in the .7 second to 2 second ballpark but I keep getting burn times in the 6 to 8 second range.  I'm fairly new to labview so any and all help is appreciated.  Thank you

[proland1121]

1) increase the frequency at which you measure.  1 second intervals are too long.  In such a case, a burn time of 0.7 seconds would actually give you a duration of zero (single datapoint)

2) split your data into two arrays (Time and Force)

Threshold the Force data to find the index at which it goes above a target value (say 10)... use index array on the time array to get the associated time.

Threshold the array again (starting at your previous location) to find when the force values return back below a target value (say 9....)  Subtraction for Delta T

[Bob_Schor]

I'm confused about the data you show.  Your VI seems to have a loop time of 0.1 sec (why is there a Wait in the acquisition loop?  Doesn't the "sampling function" have a (better) clock?  Also, the data you attached seems to have a sampling time of 1 sec, not 0.1 sec.  

Bob Schor

[amcgl556]

My apologies, the time header in the attached data set is mislabeled. It should read deca seconds (.1).    I'm fairly new to labview and the experiment setup I had required a complex (needed negative voltage so I couldnt use a MyDAQ).  I tried the threshold Idea mentioned above but I couldn't get it to work which is probably due to my inexperience lol.  Any thoughts? 

[Bob_Schor]

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@amcgl556 wrote:

... the experiment setup I had required a complex (needed negative voltage so I couldnt use a MyDAQ)...

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What does this mean?  MyDAQs can handle ±10V on their Analog inputs ...

Bob Schor

[amcgl556]

I needed +12, -12, and +5 simultaneously so I had to use a power supply 

[Bob_Schor]

If you need any serious current, you'll want a power supply.  The myDAQ gives you ±15v and +5v -- you should be able to either use the (slightly) higher voltage, or build a simple circuit to change it to ±12v (but what do I know, I'm not an Engineer ...).

Bob Schor

[proland1121]

one a side note.. please don't use decaseconds... stick to SI units and anyone taking over your software or evaluating data will have a far easier time.