In PDA measurement, the intensity of the scattered light signal from measured particles is a function of the diameter. The intensity validation compares the signal intensity from each particle with measured size, and reject erroneous results outside of acceptance bounds. This validation is performed by our state-of-art signal processor in real-time.
Intensity V.S. diameter of drops in a spray measured with PDA. These results can be validated by parabolic upper and lower bounds (valid results plotted inside the bounds as green and non-valid results plotted outside of the bounds as red) to minimize the influence from trajectory effect or slit effect
Standard PDA systems that use three detectors for size measurement can be effected by the trajectory and slit effects which are mainly seen with dense sprays. These effects can be minimized by using the intensity validation. An example of its application is show here:
Measured droplet size and signal intensity vs. position of droplet in the measurement volume.
The plot above shows the measured droplet diameter vs. position of the droplet. In positions 60 to 210, when the droplet is passing through the central part of the measurement volume, the size measurement varies less than 0.3 µ. Outside these positions, when the droplet passes through the edge of the slit, the size deviates up to 3 µ. By validating only results with intensity >500, the size variation is reduced by a factor 10.
In a real spray, the droplets may pass anywhere in the measurement volume. In such cases, the intensity validation can remove the results from droplets passing through the edge of the measurement volume, improving the size measurement accuracy.