ISOA: Tolerance on P-V power

Operand purpose

The ISOA operand adds a peak-to-valley (P-V) power term to the target surface. As specified in ISO-10110-5 Surface Form Tolerances, this operand corresponds to A in the drawing note 3/A(B/C).

Operand behaviour

During tolerancing, this operand adds sag to the target surface using a Zernike Standard Sag surface, which is added as a Composite Add-on surface. The added sag follows the Zernike Standard Sag equation with c=k=αi=0, using polynomials 4 and 1, and , for a sag equation of:

Apertures

If the target surface has a circular off-axis aperture, the Zernike Standard Sag surface will be positioned at the vertex of the off-axis surface by adjusting the tilt and decenter in the Composite property. The Clear Semi-diameter of the new surface is set to the aperture semi-diameter of the target surface, or to the Clear Semi-diameter if no aperture is present on the target surface. Apertures other than circular are not supported at this time.

Inputs
Inputs for the operand are: Surf, Units, Nominal, Min and Max.
Surf: The row number in the Lens Data Editor of the target surface.
Units: Choice of units of the Max value. 0 = units of nanometers and is currently the only option.
Nominal: The Nominal value is always 0 for this operand, indicating no added power.
Min: Always set to -Max.
Max: Specifies the largest added P-V power.
Sensitivity analysis
During sensitity analysis, the effect on the criterion is evaluated for two cases of P-V power, +Max and -Max:
MonteCarlo analysis
For MonteCarlo analysis, a random P-V power value is selected from a Gaussian distribution with a mean of 0, a standard deviation of σ=Max/2, and truncated at +/- 2σ=+/- Max.
Notes on usage of ISOA
  • ISOA may not be applied multiple times to the same surface and will trigger an error.
  • If used with ISOB and ISOC, the preferred order in the TDE is: ISOC, ISOB, and then ISOA. See discussion for the ISOC operand.
  • Note that we have removed the piston term from the power, so that a ray falling at the aperture vertex will remain unchanged and not acquire any phase.
  • ISOA should not be used with other operands that adjust power or radius of curvature, such as TRAD, TCUR, or TFRN.

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