shaft encoders angular velcocity to angular displacement

[jonhelpmejon]

I'm using two shaft encoders to determine angular twist on two opposite ends of a rotating coupling.  The outputs are in degrees/second.  How do you intergrate the velocity signals (degrees/second) to angular displacement (degrees).  I'd like to do it mathmatically in the spectrum or time wave and also for individual points at certain frequencies. 

[DuffmanSays]

Hello,

For your application, I might suggest taking a look on the mathematics pallet. There is a sub-pallet for integration and differentiation. You can provide an array of discrete inputs and these VIs can perform the required operation. Is this what you were looking for? Please post back if we can provide any further assistance!

Mike D.

[jonhelpmejon]

I'm actually looking for the conversion from angular velocity to displacement.  I.e.  How to integrate angular velocity

[NIJanell]

Hello Jon,

You should be able to find displacement by following the laws of kinematics.

displacement = original displacement + velocity * time

You can definitely use the mathematics palette to perform that operation.

Have a great week!

Janell R | Applications Engineer

[Kevin_Price]

1. As I recall, the integration functions are not (or didn't used to be -- I haven't dug down into them lately) very sophisticated.  I want to say they use the trapezoidal rule or perhaps even a rectangular approximation.  If this is indeed true, you're going to accumulate a significant amount of error in your position calculation over time.

2. Normally a device labelled as an "encoder" would encode position rather than velocity.  Is there some little interface box that's producing the velocity output?  If so, perhaps you can tap into the raw position pulse train(s).  Or perhaps what you have are tachometers rather than encoders?

-Kevin P.

[jonhelpmejon]

Thanks Kevin and everyone else.

The encoder is indeed a black box that outputs an ac coupled velocity signal (deg/s).  When I integrate the signal using a dedicated dynamic signal analyzer (Oros) to obtain deg.,  I get a difference from when integrating in Labview of about %10 in ampliltude.  Wasn't sure if Lavbiew had any quirks with this.  I appreciate your input.

[Balasundaram]

Dear John,

Just came across your question in this Forum, i am also facing the same kind of scenario, can please help in sharing the info on the encorders. The application is just simillar to yours. Currently i am looking in to Hall effect sensors.

looking forrward for your help.

thanks..Bala.

[Aashish_M]

Hello,

Are you sure you can't get position data from the encoder?

There are actually a few integration functions in LabVIEW 2009. Which one are you using and how exactly are you using it?

Here a quick overview of the point by point integral linked at KnowledgeBase 1KL99ILL: What Does the Integral x(t).vi Do?.

Kind regards,

Message Edited by Aashish_M on 03-23-2010 03:39 PM