triggering a signal to only read positive velocity

[Sully1071]

Im currently designing a system that will calculate linear velocity using a potentiometer. The velocity is multiplied by a force to give power. I only want to take readings when the velocity is positive, i have tried to set up the trigger Vi but it doesnt seem to be working. 

To be clear i want to beging measuring velocity at the point when it begings to be positive and stop it when it becomes a negative velocity. I have attached my VI.

[RavensFan]

You can't begin measuring velocity until it is positive unless you have already been measuring velocity.

The solution is to always do the measurement.  Evaluate it with a >0.  In the true condition, then do whatever it is you want to do.