Method and apparatus for headbox jet velocity measurement

Claim 1

Apparatus for measuring the headbox liquid jet velocity, said apparatus comprising: variable intensity light generating means mounted adjacent to the liquid jet for generating light such that the velocity of the jet is able to be determined; first bifurcated fiber optic light coupling means disposed between said generating means and the liquid jet for conducting light between said generating means and the liquid jet; first light sensing means disposed adjacent to said generating means for sensing light generated by said generating means and conducted through said first coupling means and reflected from the liquid jet back through said first coupling means; first signal generating means electrically-connected to said first light sensing means for generating a first electrical signal proportional to said light reflected back towards said first sensing means; second bifurcated fiberoptic light coupling means disposed between said generating means and the liquid jet, said second coupling means being disposed downstream relative to said first coupling means for conducting light through said second coupling means between said generating means and the liquid jet; second light sensing means disposed adjacent to said generating means for sensing light generated by said generating means and conducted through said second coupling means and reflected from the liquid jet at said downstream disposition back through said second coupling means; second signal generating means electrically-connected to said second sensing means for generating a second electrical signal proportional to said light reflected back toward said second sensing means; high pass filter means connected to said first and second signal generating means for filtering out components of said first and second signals below a predetermined frequency; amplifier means connected to said high pass filter means for amplifying the filtered first and second signals; analyzing means connected to said amplifier means and operable to cross correlate AC components of the amplified first and second signals for obtaining an output representing the velocity of the liquid jet; adjustable mounting means connected to said first and second coupling means for permitting adjustment of the spacing between said first and second coupling means, and for permitting adjustment of the horizontal skew of said first and second coupling means such that the optimum sensitivity of the apparatus is obtained and any misalignment of the coupling means relative to the direction of flow of the jet may be compensated for; and said first and second coupling means having elongate ends adjacent to the surface of the jet for generating first and second light spots respectively on the surface of the jet, said spots being elongate in a direction transverse to the direction of flow of the jet such that misalignment of said spots relative to said direction of flow results in substantially the same surface area of the jet flowing past said first and second spots so that said first and second signals are substantially the same.