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PDI: Phase Doppler Interferometer
Droplet size and velocity measurements

  • Measurements are based on the wavelength of light that is known to high accuracy and does not change due to environmental conditions

  • The size of the sample volume can be easily controlled and made as small as the largest droplet to be measured (or even smaller)

PDI Advantages
Droplet image

Advantages of the PDI Method for Particle Sizing

  • Response is to ballistic or singly-scattered photons; secondary light scattering is not detected

  • Signals have a unique sinusoidal character making them easily detectable with high reliability using digital techniques

  • Simultaneously measures the size, velocity, and time-of-arrival of every drop

  • Forms a direct measurement of the size distribution

  • Droplet size range capability of 0.5 μm to 2000 μm or greater

  • LWC capability from 0 to 100g/m3 or larger

  • Measures in droplet number densities to 100,000/cc, depending on droplet size

  • High data rate capability of >100,000 drops/second without loss of readings

  • In situ measurements of the sample volume size allowing determination of droplet number density, flux and LWC

  • Reliable detection and rejection of ice particles from the droplet size measurement

PDI System Components

The complete PDI  instrument includes:

  • optical transmitters

  • optical receiver

  • ASA signal processors

  • AIMS system software

  • data management computer


PDI systems are available in both modular and

self-contained configurations.

The laser wavelengths and power can be customized

based on the application and user needs.

The Artium PDI design incorporates several features aimed at ease-of-use and data accuracy. A key feature is the ability to change the droplet size measurement range without requiring the user to change lenses or realign the optics. This can be accomplished by changing the laser beam separation and selecting different masks in the receiver via software. A software controlled aperture
module also allows for the selection of a variety of apertures and tilts. A new version of the ASA is now available for improved data accuracy at high speeds in dense environment. The AIMS software includes an auto-setup feature that automatically selects the processor and optics settings for optimal performance in complex sprays.

Key features that are unique to Artium’s PDI include:

  • Built-in, high-powered DPSS lasers to enable backscatter measurements through contaminated windows.

  • Automated instrument setup features to simplify instrument operation in difficult environments (U.S. Patent 7,564,564, 2009)

  • Digital signal detection and full complex Fourier transform signal processing for frequency and phase

  • Automatic selection of size range through computer selection of beam intersection angle and beam expansion

  • Automatic selection of size range through computer controlled mask selection in the receiver covering at least three size ranges

  • Signal intensity validation logic

  • Three phase measurements for improved particle measurement reliability and accuracy and rejection of trajectory errors

  • Option fourth phase measurement for improved measurement accuracy in dense spray application

  • Full complex Fourier transform signal processing with up to 100,000 samples in the signals

  • Advanced signal validation logic including tests for variations in frequency and phase over the duration of the Doppler signals (U.S. Patent Pending)

  • Computer selectable sample volume size to minimize coincidence errors

PDI Components

System Components

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