ME 102A Spring 2010 May 4, 2010 Jennifer Lew Stephen Tu

 Fans cool a computer  Rotational Speed  Cooling Capacity   CPU would almost instantly melt CPU: Fan Grid:

 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: Fan:

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: Phototransistor:

Measurement Power Breadboard

Measured range Nominal RPM 95% Confidence Interval

IssueSolutionDrawback 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 errorAllow user to specify number of iterations before displaying the mean value of iterations Increases accuracy but increases processing time