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ME 102A Spring 2010 May 4, 2010 Jennifer Lew Stephen Tu. FSD – Fan Speed Detector. Motivation. Fans c ool a computer Rotational S peed C ooling C apacity CPU would almost instantly melt. CPU: http://hardforum.com/showthread.php?t=1423185 - PowerPoint PPT Presentation
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FSD – Fan Speed Detector
ME 102A Spring 2010May 4, 2010
Jennifer LewStephen Tu
Motivation
Fans cool a computer Rotational Speed Cooling Capacity CPU would almost instantly melt
CPU: http://hardforum.com/showthread.php?t=1423185Fan Grid: http://forums.legitreviews.com/about12716.html
How It Works
Idea: Use fan blades as an Optical Encoder By measuring the number of pulses in a fixed period of
time, can determine speed of blades
Rotary: http://hades.mech.northwestern.edu/index.php/Rotary_EncoderFan: http://computershopper.com/shoptalk/components/silverstone-fm83-cram-more-fan-into-the-same-space
Implementation
1. Fan Voltage Supplied Current Supplied Impellers
2. Sensors Infrared LED Phototransistor Circuit: Resistors, Voltage Supplied
3. LabVIEW VI Input number of impellers Implements GenerateCalibrationCurve() Displays RPM, voltage supplied to fan
4. Error Analysis Sensor is noisy, so must take many samples and
consider confidence intervals
Procedure for calibrating fan
IR LED: http://www.solarbotics.com/assets/images/ir-led/ir-led_pl.jpgPhototransistor: http://farm3.static.flickr.com/2325/2105641666_1487ce594e.jpg
Layout
Measurement
Power
Breadboard
Results
IssuesIssue Solution Drawback
Current limit on power supply
Use analog lab equipment that does not impose as stringent current limits.
Makes the UI less robust, due to less automation
Fluctuations in ambient light
Limit RPM readings to phototransistor voltages of magnitude greater than 1.5 mV. Below 1.5mV-> RPM=0
The threshold voltage is not appropriate for all conditions
Precision error Allow user to specify number of iterations before displaying the mean value of iterations
Increases accuracy but increases processing time
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