How It Works

The short answer: the LaserSpeed projects an interference patternA pattern of light and dark stripes of light. Also called a fringe pattern on the surface to be measured.
As the product moves, light is scattered back to the LaserSpeed at a frequency proportional to the speed
of the material. The freqency is measured, converted to a speed and pulses are generated at a rate proportional to the speed. External counters or PLCs count the pulse to determine length.

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The LaserSpeed has one laser diode source but it is split into two beams that exit the gauge aperture at an angle. The two beams converge and overlap at the standoff distance.The distance from the front of the gauge to the center of the depth of field The overlap region is called the depth of field.The vertical measurement region of the gauge. Measurements can be taken within this region

The fringe patterns are generated by the two laser beams exiting the LaserSpeed.

If you take two coherent light sources that are the same wavelength and cross their paths at an angle, a fringe pattern is generated. As the waves of light cross
each other, the peaks line up to create
a light stripe. As they continue to cross,
the peaks and troughs line up to cancel each other out. This pattern repeats throughout the depth of field.The vertical measurement region of the gauge. Measurements can be taken within this region

The formulas to the right show the mathematics behind the measurement principle. 'd' is the fringe spacing. 'f' is the frequency, which is determined by
the scattering As a particle on the surface moves through the light and dark stripes of the fringe pattern, a time varying signal is generated and read by the LaserSpeedof light from the measurement surface. Since 't' (time) is the inverse of frequency, we have the two parameters to calculate velocity, 'v'.

Length is determined by integrating velocity over time.

While it is not important to memorize the formulas, it is important to
understand that the spacing 'd' is determined by wavelength, λ, and beam
angle, κ. Furthermore, the two parameters can be controlled and held contstant. This means, 'd', the fringe spacing, never changes.

If 'd' never changes, then the LaserSpeed never needs recalibrating!

How does the LaserSpeed convert
internal length and speed to a usable interface?
The primary interface is through pulses. The LaserSpeed can be configured
to any pulse/unit length (ie resolution). Once this is configured, pulses will
be generated at a rate which is equal to the speed of the material multipled
by the resolution.

If only a positve speed and direction is needed then one pulse channel is enough.

If direction information is required then two chanels are needed.

This is called quadratureQuadrature x1 mode - The counter adds 1 count after A then B goes high
Quadrature x2 mode - The counter adds 1 for each falling edge of A and B
Quadrature x4 mode - The counting devices adds 1 for each rising and falling edge of A and B counting. Two channels, A and B, generate pulses 90 degrees out of phase.
If A leads B, then the direction is positive. If B leads A, then the direction is negative.

Both True and False signals are generated for added noise immunity.