How can I calculate the slope of an isometric torque curve with a trigger and time increments of 0-30ms, 0-50ms, 0-100ms etc....

I am analyzing isometric muscle contractions of the quadriceps and want to calculate the rate of force development (not just peak torque) for the torque-time curve. I want to set a trigger so that the slope of the torque curve is calculated when 7 newton-meters is reached. From there I'm trying to calculate the slope in time increments of 0-30ms, 0-50ms, 0-100ms, etc....My data is sampled at 2000 Hz and written in text files. Below is a copy of the VI I have developed so far. I am very new to programming with LabVIEW but can definitely see its potential! Any advice would be greatly appreciated.
Attachments:
Dissertation Isometric RFD.vi ‏14 KB

Fiddler918,
When trying to implement something like this in LabVIEW, it is often helpful to think about how you would program this function in a traditional text-based language. Try and break the problem down. You need to locate the data point in your array that is 7 Nm or greater. At this point, you will need to grab the data points that are 60 indices (for the 30ms gap, assuming your points are equally spaced 0.5 ms apart), 100 indices (for the 50 ms gap), and 200 indices (for the 100ms gap) ahead of this point in your data file, and calculate the slope using pairs of data points.
Here is a general description of a possible implementation of this code:
You can wire the appropriate column of the data array into a For Loop on the block diagram and have it auto index through the points. If you right click on the Use the Greater or Equal? function to generate a Boolean that will be true when you want to exit the For Loop. Right-click on the border of the For Loop and select Conditional Terminal. This will cause a small stop sign to appear. If you wire the Boolean to the conditional terminal, the loop will stop at the value that is greater than or equal to 7 Nm. If you wire the Loop Iteration terminal out of the For Loop to the right, this will give you the index of the value in the column that you’re interested in. Having this value, you can then use the Array functions to grab the specific data points you need, and numeric functions to perform the necessary math.
If any of this didn't make sense, the LabVIEW help files are a great resource to use.
Here is a link to some video tutorials of the LabVIEW programming environment. They may help you in the development of your code.
http://www.ni.com/academic/students/learnlabview/
Regards,
Jared R.
Precision DC Product Support Engineer
National Instruments

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