Internal and external filters

Applicable Standards

Both filter types adhere to industry-specific regulations, including:

• ISO 10526 (Standard illuminants for colorimetry, e.g., D65, A light sources)
• ASTM E1164 (Practice for obtaining spectrophotometric data for object-color evaluation)
• MIL-STD-810G (Environmental engineering considerations for military equipment, including filtration)
• IEC 60529 (IP ratings for dust/water resistance in external air filters)
• NSF/ANSI 42 & 53 (Standards for drinking water treatment filters)

Main Parameters

Working Principle

• Internal Filters:
  • Operate via interference, absorption, or diffraction to modify light spectra.
  • Example: A UV-cut filter in a camera blocks ultraviolet wavelengths to improve color accuracy.
• External Filters:
  • Use mechanical, electrostatic, or chemical media to trap particles/contaminants.
  • Example: A HEPA filter in an HVAC system captures 99.97% of 0.3 µm particles.

Test Principle & Applications

• Optical Testing (Internal Filters):
  • Spectral Transmittance: Measured via spectrometers (e.g., ISO 13655).
  • Applications: Color calibration, fluorescence microscopy, solar simulation.
• Environmental Testing (External Filters):
  • Particle Retention Efficiency: Tested per ASHRAE 52.2 (air filters) or NSF protocols (water filters).
  • Applications: Cleanrooms, medical facilities, industrial emissions control.

Key Considerations:

• Internal Filters: Require precision alignment and material durability (e.g., fused silica, coated glass).
• External Filters: Must balance efficiency with airflow/flow rate (e.g., MERV ratings for HVAC).

Both internal and external filters play pivotal roles in optimizing system performance, ensuring compliance with regulatory standards, and enhancing product reliability across industries.