Visual Search Kit, the Dome Scratcher Test Set for MIL-PRF-13830B 40-20 scratch-dig inspection.

Introduction

The Visual Search Kit is a highly specialized, precision-engineered optical inspection system developed for evaluating the surface integrity of infrared (IR) sensor domes used in advanced aerospace and defense platforms. These domes, particularly those associated with missile warning systems such as PAWS, play a critical role in detecting incoming threats. Any degradation in optical quality directly affects detection accuracy, response time, and overall mission safety. The Dome Scratcher Test Set translates laboratory-based MIL-PRF-13830B standards into a portable inspection solution that can be used directly on aircraft without dismantling or transporting components.

Optical measurement and reticle system

At the core of the system are the precision 10X scale loupes. Each loupe is fitted with an engraved glass reticle acting as a calibrated measurement scale. When the loupe is placed directly on the optical surface, the reticle overlays the image, allowing direct measurement of defect dimensions without external measuring tools.

• Linear reticles (#3, #4, #STD): aligned perpendicular to a scratch to read its width directly from the scale.
• Circular reticles (#7): fit the smallest enclosing circle around a dig to measure its diameter.
• Mixed geometry reticles (#1, #2): used for complex defect analysis and alignment on curved surfaces.
• White reticle variants (#STDW, #4W): provide enhanced visibility on dark or coated optical surfaces.
• Inch-based reticles (#5, #13): enable compatibility with legacy aerospace standards and OEM documentation.

Measurement principles and accuracy

The system operates on the MIL-PRF-13830B scratch-dig classification method: the scratch number represents the width of the widest scratch in 0.001 mm units, and the dig number represents the diameter of the largest pit or inclusion in 0.01 mm units. For example, a 40-20 specification means a maximum scratch width of 0.040 mm and a maximum dig diameter of 0.20 mm. Accuracy is ensured through precision-engraved reticles, stable contact-based measurement with the loupe resting on the surface, high-quality optics with consistent magnification, and comparator plates for reference validation.

Illumination and defect detection

Proper lighting is critical for identifying optical defects. The system incorporates two types of illumination:

• White LED illumination: used for general inspection and detection of visible defects such as scratches, surface contamination and haze.
• UV LED illumination (365 nm): used for advanced inspection to detect coating cracks, delamination, sub-surface anomalies and fluorescent contamination not visible under normal lighting.

Cleaning and surface preparation

Accurate inspection requires a contamination-free surface. The system includes a complete cleaning setup:

• Air blasters: non-contact cleaning that removes loose dust and particles without touching the surface.
• Microfiber cloths: gentle cleaning without damaging coatings.
• ESD finger cots: prevent electrostatic discharge and contamination from skin contact.

Inspection workflow

• Preparation: verify equipment and confirm clean, well-lit conditions.
• Surface cleaning: remove dust using the air blaster, then clean with microfiber cloth if required.
• Scratch inspection: use linear reticle #3 to measure and record scratch widths.
• Dig inspection: use circular reticle #7 to measure and record dig diameters.
• UV inspection: identify coating defects invisible under white light.
• Evaluation and documentation: compare measurements against MIL standards and record pass/fail results.

Reliability, maintenance and longevity

Loupes are factory-calibrated and require minimal maintenance; components are replaceable and supported with spares from the Spare Kit module. Routine maintenance includes cleaning optical components, verifying calibration annually, and replacing consumables such as cloths and batteries. The IP67-rated case protects against environmental damage throughout the equipment's service life.

Conclusion

The Dome Scratcher Test Set represents a complete, field-ready solution for optical surface inspection in aerospace applications. By combining precision measurement tools, advanced illumination and rugged portability, it enables accurate defect evaluation directly at the point of use — enhancing inspection efficiency, ensuring compliance with stringent standards, and supporting critical airworthiness decisions.