Sinusoidal Phase Shift

[ericgibbs]

We have a linear sensor that gives out two sinusoidal signals 90 degrees apart, these are put through an interpolator (which we cannot play with the electronics inside) and then into a PC for Transmission Error Measurement. The problem we are facing is a large error on the PC, which is caused by the two signals not being exactly 90 degrees apart. There is approximately 2-3 degrees of error.

hi,
Thanks for the explanation, I'm still kicking myself for misreading your posted limits.

 

[MikeMl]

We have a linear sensor that gives out two sinusoidal signals 90 degrees apart, these are put through an interpolator (which we cannot play with the electronics inside) and then into a PC for Transmission Error Measurement. The problem we are facing is a large error on the PC, which is caused by the two signals not being exactly 90 degrees apart. There is approximately 2-3 degrees of error.

Since you are putting the final result into a computer, presumably by using an A/D Conveter between the interpolator and the computer, why dont you just junk the interpolator, A/D both of the quadrature signals, and do your own interpolation inside the computer in software.

If linearizing the interpolation requires phase-shifting one of the quadrature signals relative to the other, this becomes a trivial operation once the signals are digitized. I'll bet that the interpolation is no more complicated than a vector multiply.

 

[meastwood98]

The problem is that the interpolator and the computer software is something that is a permanent setup that we use with various different linear and rotarty encoders. Therefore the solution we want is to be able to just plug the sensors in as we would with an encoder without editing any software or the interpolator.

The sensors themselves only cost approx £5 and therefore cannot really be expected to give the same accuracy as an expensive encoder, however we were just interested if we could manipulate the signals to get somewhere close.

If it cant be done its not a problem, thanks anyway.