Want to know more?
The LaserSpeed Pro 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 Pro. 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 LaserSpeed Pro of 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 Pro never needs recalibrating!

How does the LaserSpeed Pro convert
internal length and speed to a usable interface?
The primary interface is through pulses. The LaserSpeed Pro 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 quadrature Quadrature 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.