Temperature Coefficient of Temperature Coefficient of Radiant - PowerPoint PPT Presentation

Temperature Coefficient of Temperature Coefficient of Radiant Sensitivity of Silicon Radiant Sensitivity of Silicon Photodiodes for SIM Photodiodes for SIM Presentation by: Presentation by: Brian Kirby Brian Kirby Mentors: Mentors: Jerry Harder Jerry Harder Erik Richard Erik Richard

Outline Outline  Background on the SIM instrument Background on the SIM instrument   Radiant sensitivity and why it Radiant sensitivity and why it’ ’s important s important   Experiment Experiment   The setup The setup   How data was taken How data was taken   Results Results   The next steps The next steps   Summary Summary   Celebrate the end of presentations Celebrate the end of presentations 

Spectral Irradiance Monitor Spectral Irradiance Monitor  SIM monitors the solar SIM monitors the solar  spectral variability spectral variability  Scans the solar spectrum Scans the solar spectrum  9-13 times a day 9-13 times a day  This data is crucial in This data is crucial in  understanding: understanding:  The Sun The Sun   Climate change on Earth Climate change on Earth 

SIM: What it does SIM: What it does  Measures solar irradiance Measures solar irradiance  between 200 and 2700 nm between 200 and 2700 nm  About 96% of total solar About 96% of total solar  irradiance irradiance  Uses electrical Uses electrical  substitution radiometer as substitution radiometer as primary detector primary detector  Incorporates four Incorporates four  additional photodiode additional photodiode detectors detectors

SIM: How It Works SIM: How It Works  A prism and reference A prism and reference  mirror are controlled by mirror are controlled by a voice coil a voice coil  The prism disperses the The prism disperses the  light into its different light into its different wavelengths on the wavelengths on the diodes diodes  The mirror directs light The mirror directs light  onto the charged onto the charged coupled device to sense coupled device to sense what wavelengths are what wavelengths are being measured being measured

Are You Paying Attention? Are You Paying Attention?  What does SIM stand for? What does SIM stand for?   Spectral Irradiance Monitor Spectral Irradiance Monitor 

Scope of Project Scope of Project Scope of this project

Radiant Sensitivity of Photodiodes Radiant Sensitivity of Photodiodes  Ratio of output current to light power received Ratio of output current to light power received   Amps/watt Amps/watt   Function of wavelength and temperature Function of wavelength and temperature   Measured at all wavelengths at a controlled Measured at all wavelengths at a controlled  temperature temperature R , T R , T 1 T T ( ) ( ) ( ) � = � � + � � � � � 0 0 1 1 1 0  Scaled to the temperature of diodes at time of reading Scaled to the temperature of diodes at time of reading  R , T R , T 1 T T ( ) ( ) ( ) ( ) � = � � + � � � � � � � 0 0 o

Radiant Sensitivity of SIM Diodes Radiant Sensitivity of SIM Diodes  The radiant sensitivity curves are plotted against wavelengths The radiant sensitivity curves are plotted against wavelengths  bellow bellow  These curves will scale if the temperature changes These curves will scale if the temperature changes   If not taken into account, the solar irradiance data will be wrong If not taken into account, the solar irradiance data will be wrong 

SORCE SIM Measured Temperatures (June 14, 2008) SORCE SIM Measured Temperatures (June 14, 2008) SORCE SIM Temps  If not taken into If not taken into ESR  26 CCD Pixel 12000 account, these account, these 25 Diode, Vis1 temperature 24 temperature Diode, Vis2 23 changes could changes could Diode, IR 22 Temp (C) Diode, U V cause false data cause false data 21 CCD Pixel 1 that could be that could be Case, front aperture 20 mistaken for mistaken for Case, near focalplane 19 Case, near center changes in the changes in the 18 Case, near prism drive solar irradiance solar irradiance 17 90 180 270 360 prism Time (min)

The Beta Angle The Beta Angle Courtesy of NASA http://spaceflight.nasa.gov/station/flash/start.swf

Beta Angle’ ’s Effect on Temperature s Effect on Temperature Beta Angle

Are You Really Paying Attention? Are You Really Paying Attention?  What is Radiant Sensitivity? What is Radiant Sensitivity?   Amps of output current/watt of power received Amps of output current/watt of power received  by the detector by the detector

Experiment to Measure Temperature Experiment to Measure Temperature Coefficient Coefficient Simulate Sun With Split the Lasers Beam Test 50% Photodiode 50% Constant Temperature is Kept at room intensity changed. temperature. Control and wavelength Temperature is Temperature is Photodiode monitored along with monitored along output voltage. with output voltage.

Pictures of Experiment Pictures of Experiment

Laser Driver Laser Driver  Laser is kept at constant Laser is kept at constant  intensity and wavelength intensity and wavelength  Thermoelectric cooler Thermoelectric cooler  keeps laser at a constant keeps laser at a constant temperature to maintain temperature to maintain consistent wavelength consistent wavelength  Monitors laser output and Monitors laser output and  corrects current to corrects current to maintain constant maintain constant intensity intensity

Photodiode Mounts Photodiode Mounts  Thermoelectric Coolers Thermoelectric Coolers  change temperature of change temperature of photodiode photodiode  Operational amplifier Operational amplifier  allows us to easily allows us to easily monitor the monitor the photodiode’ ’s output s output photodiode voltage voltage  Thermistors Thermistors allow for us allow for us  to monitor the to monitor the temperature of the temperature of the photodiode photodiode

Who Wants Candy? Who Wants Candy?  What is the purpose of enclosing the experiment What is the purpose of enclosing the experiment  in a box? in a box?  To assure we To assure we’ ’re monitoring how the radiant re monitoring how the radiant  sensitivity changes at a specific wavelength sensitivity changes at a specific wavelength

Gain Experiments Gain Experiments  Tested the two Tested the two  photodiode circuit photodiode circuit boards for differences in boards for differences in gain values gain values  Also tested how the gain Also tested how the gain  changed with changed with temperature temperature

Recording the Data Recording the Data  LabView LabView code monitors code monitors  several channels on a several channels on a Keithley Multimeter Multimeter Keithley  The data can be The data can be LabView Virtual  Interface monitored during the monitored during the experiment experiment  The readings are also The readings are also  saved in a text file for saved in a text file for post experiment analysis post experiment analysis LabView Block Diagram

Procedure for Taking Data Procedure for Taking Data  Data was taken at 670nm, 830nm and 904nm Data was taken at 670nm, 830nm and 904nm   Each wavelength was tested at a range of Each wavelength was tested at a range of  temperatures temperatures  Each temperature test lasted one hour Each temperature test lasted one hour   Before and after each test a baseline test was Before and after each test a baseline test was  conducted conducted

Procedure for Analyzing Data Procedure for Analyzing Data  The data was imported into IDL The data was imported into IDL   Statistics were done on all experiments to verify good Statistics were done on all experiments to verify good  data was taken data was taken  Baseline reading were taken into account Baseline reading were taken into account   The ratio of test diode output to the control diode The ratio of test diode output to the control diode  output was graphed output was graphed  A line was fit to the data using a A line was fit to the data using a bivariant bivariant least squares least squares  fit method fit method  This line is the temperature coefficient of radiant sensitivity This line is the temperature coefficient of radiant sensitivity 

Eliminating the Baseline Reading Eliminating the Baseline Reading

Results Results

The Next Steps The Next Steps  Phased experiment needs to be created Phased experiment needs to be created   More wavelengths need to be measured More wavelengths need to be measured   The lasers need to be tested accurately The lasers need to be tested accurately 