Problem of Noise during Phase Unwrapping

Question

Hello!
I am using VISION based system to measure phase in a displacemnt measuring interferometer.My phase algorithm gives a wrapped phase as expected saw tooth wave profile whose unwrapped value I am taking with help of a loop which counts each jump from -pi to +pi or vice versa. Problem is that even after using filter noise is not possible to be eliminated practically and if data capturing becomes slow near this edge i.e.where -pi or +pi is aproaching due to noise large number of false count results. To solve this I thought using two different algorithm which gives slightly offset curves so that when pi point is approaching in original one second one is still away from that point and any false jump can be eliminated by comparison.The total phase value can be compared from earlier value in both window and any increase or decrease should agree in each algorithm. this will avoid this practical problem.Can any one suggest me how to go about this problem in LabVIEW or any other solution.
Thanking you,
Ajay Shankar
Ajay Shankar

Answer 1

The attached VI will take care of phase jumps in either direction. I developed this for another project and it may need modification for your application.
Have you tried a smoothing filter or sliding window averager to get rid of your noise? These often work better than a simple lowpass filter.
When the system is moving slowly or stopped recalling the last valid position and allowing only small adjustments to it may prevent the big jumps. In other words, if you can't beat the noise, ignore it. This can be easy to talk about but is not always so easy to implement.
Lynn
Attachments:
Phase Unwrapper.vi ‏51 KB