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)

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.

Main Parameters