DEC10-06: Frozen Precipitation Detection

System for SODAR Systems by Ashor Chirackal, Imran Butt and Michelle Tan

Advisor: Prof. Tim BigelowClient: Mr. Doug Taylor

(John Deere Renewables)

What is a SODAR?

SODAR (Sonic detection and Ranging) Generates sound pulse and listens for the echo

from the atmosphere to detect the changes in the reflected wave

Uses Sound pulse to measure wind shear Based on those changes calculates the speed at

that height A SODAR system is used to measure wind shear

for up to 200 meters.

What is a SODAR?

The SODAR system that we are currently working with is the 4000WE model designed by the Atmospheric Systems Corp. (ASC).

John Deere has several of these SODAR systems located at different wind farms for data collection.

The SODAR is primarily powered by a solar panel and has a generator as a secondary source

Top View(Operations)

What's wrong with SODARs

SODARs need the reflector board to be clear of obstacles

Over winter snow gets accumulated on the reflector board and corrupts the readings

The current snow detection is ineffecient and needs to be replaced

Problems Elaborated

Normal Operation

Problems Elaborated Distortion in the sound reflection due to

accumulation of snow (on left) and un-even ice (on right)

Effects Current system is inefficient in detecting

snow Has many false positives.

Heater is turned on when not required (in rain) Inefficient control of the heater

Used longer than is actually required This results in high power consumption which

leads to hibernation mode Since SODARs are located remotely it is very

difficult to get the maintenance out to fix the SODARs

Problem Statement

Optimizing the number of times the heater is turned on to reduce power consumption by designing a more efficient and accurate method to detect the conditions in which the SODAR equipment needs to use the heater. The necessary conditions and requirements are outlined below: Able to tell the difference of snow and ice accumulation on

the reflector plate. Able to detect powdery snow that distorts the SODAR

readings and needs to be melted. Able to tell how much snow is present to calculate the time

the heater should run

Conceptual Sketch

Conceptual Sketch•The main Idea is to use passive sensors to detect snow

accumulation

•Use the sound waves generated by the speakers to our

advantage

•Piezoelectric sensors could be used by placing them on top of

the reflector pad

•There will be changes in the voltage signal when the surface

is clear of snow as compared to surface covered with snow

Concept Sketch

Concept In detail

Functional Requirements

Power consumption Lower than the current system.

More efficient in terms of power consumption to delay hibernation mode. ( 25 Watts)

Reduce the number of times the heater is turned on.

Heater Control Heater should not be used if smooth and flat ice layer is present. water or rain is present. Heater should be used if there is an accumulation of snow that interferes SODAR

operation Variance of ice on the reflector pad

Functional Requirements

Frozen precipitation detector can tell the difference between snow and ice

accumulation on the reflector pad.Quarter Inch

can detect a variance on the reflector pad. must withstand the temperature of the heating

pad. must not interfere with the acoustic environment

of the SODAR

Non-functional Requirements

Financial Economical and affordable.

Within $500 Limited Budget (subsidized by John Deere).

Installation/Manufacturing/ Maintenance Simple. Adaptable. Easy to maintain. Reliable.

Non-Functional Requirements

Weather Must be able to withstand various weather conditions

i.e. snow storms, blizzards 100F to -30F

Rain or flat layer of snow or ice will not be an issue as long as they do not disrupt with the operations of the SODAR system

System Diagram

Technical Considerations

1) Microprocessor It needs to have the right amount of input/output

ports to collect data from the sensors and control the operation of the heater. This will also depend upon the number of piezoelectric

plates The processor speed needs to be high enough to take readings from the sensors and analyze them.

C language will be used to program the microprocessor.

The output signal to run the heater must be in standard TTL.

Technical Considerations (cont.)

2) Piezoelectric plates The piezoelectric plates should have the

material strength to with stand the temperature extremes of the environment.

The response of the piezoelectric plates must be clear enough to be analyzed by the microprocessor.

3) Secondary sensors Secondary sensors, if employed, will change

some requirements of the microprocessor

Market Survey The Frozen Precipitation Detection project is very unique to the client’s

needs and specification.

The piezoelectric sensors are used in other applications such as quality assurance, process control, measurements of various processes etc.

Their use in detecting snow is very unique and we haven’t been able to find an application of piezoelectric sensors that are used in detecting snow or ice.

Some applications where piezoelectricity is used are outlined below Detection and generation of sonar waves Power monitoring in high power applications Automotive engine management systems Acoustic emission testing Inkjet printers

Potential Risks

Light snow that is less dense with more air pockets might not be detected by the piezoelectric sensor.

A secondary sensor will be put in to make the system more effective.  The secondary sensor will act as a back-up system.

The project might not be able to be tested under the right weather conditions. Starts in Spring and ends in Fall (No snow !!!)

Potential Risks

Piezoelectric Plates are custom made and most manufacturers have a minimum order of $500!!

Resource estimates

Functional Decomposition The piezoelectric sensors

will be placed either on top of the heating pad or underneath the fiber glass layer of the reflector pad.

The output from the SODAR speakers will be the input for the piezoelectric sensors.

A weather sensor is connected which will provide the outside temperature. The secondary sensor represents an optional sensor that might compliment the primary sensor.

Functional Decomposition A microcontroller

is used with the previous sensors to determine optimal heating times. Our plan is to integrate this microprocessor with the piezoelectric sensor and the secondary sensor.

C programming is to be used to program the microprocessor.

The piezoelectric sensor and the secondary sensor must be in sync with each other. In order to integrate these sensors, we will program the microprocessor using C programming.

Detailed Design

Our final implementation will be highly influenced by our test results. Currently our team has two ideas to implement the piezoelectric solution for our project. The difference in the two ideas is the location of the piezoelectric plates on the SODAR System.

On the heating pad Underneath the fiber glass layer

Layers of the Reflector Pad

Detailed Design The first Layer is the Heating

surface

The second layer is a fiber glass layer. The purpose of the fiberglass is to reflect the sound energy into the atmosphere.

Underneath the Lead layer is the frame to hold all these layers. The manufacturer has allowed us to use up to 1 inch of spacing after the Lead layer.

Alternative for Piezoelectric plates

Since the spacing under the fiber glass is wide, the team might decide to use microphones instead of piezoelectric Microphones are easier to implement as

compared to piezoelectric

Detailed Design

If our team finds it more feasible to place the sensors underneath the fiber glass layer, it will be easier to protect the sensors from weather conditions.

Further spacing allows us to use microphones for sound detection instead of piezoelectric sensors. The microphones will greatly simplify the implementation of our project.

HW/SW Technology

The SODAR uses a computer system onboard. Currently, the computer is used for data

collection. The computer uses a Linux operating system and

is programmed using the C language. If required this computer system might be used to

do some data processing for our sensors

Test Plan Obtaining several types of piezoelectric plates that will potentially work for the

project. Testing the piezoelectric plates and analyze their characteristics. Testing the piezoelectric plates with snow and ice conditions/ temperature

conditions. Obtaining a microprocessor and programming the microprocessor using C

language. Connecting the piezoelectric sensors with the microcontroller and the

temperature sensor. Measure the sound waves on the current SODAR system to determine

installation placement and feasibility of the design. If feasible, high level testing/simulation will be conducted where multiple

piezoelectric plates will be placed and connected on a board (under a fiber glass or above a rubber pad) with inputs from the temperature sensor.

Test Plan: Where to place the sensors? Directly on the reflector pad

Placing piezoelectric directly on the reflector pad has some advantages and disadvantages.

Advantages: The strength of the sound pulse will be strong enough for the piezoelectric

plate to pick up the signal and give a good electrical signal. It will be simpler to differentiate between the case of a clear reflector board

and a board covered with snow. This is because the snow will be directly covering the surface of the piezoelectric and the difference in the response of the piezoelectric will be easier to identify

Disadvantages: The piezoelectric will be directly impacted by the weather conditions (rain

snow etc) The piezoelectric might absorb some sound energy which is crucial for the

SODAR measurements

Our test approach will include these considerations and compare the advantages and disadvantages of this approach and verify the usefulness of placing piezoelectric on the reflector pad.

Test Plan: Where to place the sensors?

Under the fiber glass layer of the reflector pad Advantages

The mounting of our sensors will be simplified as our sensors (piezoelectric or microphones) will not be exposed to the outside weather.

Disadvantages: The strength of the sound pulse will be reduced and it might be more

challenging to detect a sound pulse as fiber glass is a good reflector of sound

Interference of sound from other sides of the SODAR For our design we are more interested in the sound pulse

coming directly from the speakers. Based on the distortions created by snow accumulation the microphones will generate a different signal.

If the strength of that sound is weaker as compared to the sound interference from other sides of the SODAR then it will be difficult to identify the presence of snow.

Unit Testing of a Piezoelectric

Testing Setup

Testing Equipment Used

Piezoelectric Plate Images Scientific Instruments PZ-04

Krohn-Hite Filter Speaker Function Generator Oscilloscope Amplifier Circuit

Generated Signal

Without any input

Outputs

A peak at 3.5 Khz; which was the frequency of the speaker placed on the piezoelectric

Output: Unit Test (Peak Detection)

A peak at 3.5 Khz; which was the frequency of the speaker placed on the piezoelectric

Current Status

Present: Unit testing Found a company that will provide us the piezoelectric

plates without minimum order. (Noliac)

Future: Ordering a piezoelectric plate that fits our specs (curie

temperature, thickness, detects sound) Amplifying circuit that will work best with the piezoelectric

that we are working with.

Contributions

Ashor Chirackal Team Leader Hours: 60

Michelle Tan Communications Hours: 50

Imran Butt Webmaster Hours: 55

Plans for next semester

Visit the SODAR and measure sound pressure

Order parts More testing Programming the microprocessor Build a prototype Test out on SODAR

Questions?