Disdrometer Love Rain on My Parade By Josh Molzan Steve Gronstal

What the Heck is a Disdrometer An instrument to measure the drop size distribution falling hydrometeors Three main types: –Video disdrometers –Acoustic disdrometers –Impact disdrometers

An Impact Detector Momentum transferred: –P = Mass * Velocity –Mass = f(size) –Velocity = f(size) Basically, Size is EVERYTHING

Creating Our Disdrometer

Our Disdrometers

The piezoelectric device: What is it and how does it work? Piezoelectricity is the ability of some materials to generate an electric field or electric potential in response to an applied mechanical stress. Basically, the harder you push it, the bigger the voltage.

But its sooo small Is the detector big enough to accurately measure the rainfall distribution?

Rainfall Rate

How many drops hit per second?

So how many drops hit? Rainfall Intensity Rainfall Rate (mm/hr) Average Diameter (mm) Detector Area (mm 2 ) Hits (#/s) Light< 2.5 mm/hr Moderate mm/hr Heavy10-50 mm/hr

Experiment 1 Examining the signal of a drop on each sensor

The Good (Head 3)

The Bad

The Ugly (Head 1)

Analyze lots of drops per detector

Experiment 1: Results PeaksOscillation PeriodDecay RateAmplitude (V) Per EventStDevAverageSt. DevAverageSt. DevAverageSt. Dev Percent Deviation Head Head Head Head 4Failed Head Head Head 7Failed Head 8Failed

Experiment 2 Examine how much size matters. –Drop 4 different size drops onto our favorite detectors. –Find the relationship between Voltage response and drop size.

Creating Drops Head Fall Height (cm) Diameter (mm) Mass/ Drop (mg) Estimated Velocity (m/s) Terminal Velocity (m/s) 25G G G Buret

This Signals (H3, Buret)

Analyzing the Signal Damped Harmonic Oscillator (i.e. a spring)

Results…. But… What does it mean? PeaksPeriodDecayAmplitudeVoltage Offset Head Drop MassAverageSt.Dev.AverageSt.Dev.AverageSt.Dev.AverageSt.Dev.AverageSt.Dev

Voltage Relationships? Possibility One: –Model our system using Electrical Potential Energy –V α KE? Possibility Two: –Model our system as a spring. –V 2 α KE

Electric Potential Energy Assumptions –The KE of the raindrop is completely transferred to the detector –The initial KE is then converted into Electric Potential Energy. –The Voltage Change acts like a pt charge moving in an electric field.

Is V α KE??

Energy of a Spring Assumptions –The KE of the raindrop is completely transferred to the detector –The initial KE is then converted into Spring Potential Energy. –For Piezoelectric materials, a change in stress results in a change in potential –Capacitors have the same relationship!

Is V 2 α KE??

Log D vs Log A

Diameter 3 vs Amplitude 2

Conclusion After analyzing 250,000,000 lines of data, our results indicate Kinetic Energy is proportional to Potential Squared. More data points are needed to confirm the relationship between particle diameter and voltage response! With more work, a piezoelectric transducer will make a decent disdrometer.

Future work to do: Experiment with smaller drop sizes (< 2mm diameter). Experiment with drops at terminal velocity. Experiment with an oscilloscope that can handle larger voltages. Determine the voltage variation due to drop impact location. Move analysis to real-time…..