1. Motor Speed Sensing By Eric Hall

2. Problem Overview

3. Problem Overview (cont.) Router will cut the stock material Router uses induction motor Constant bit speed and RPM required

4. Solution Closed loop micro-controlled system Closed loop micro-controlled system Router bit RPM sensor Router bit RPM sensor

5. Which Sensing Method? Methods considered: Frequency to Voltage Frequency to Voltage Shunt Shunt Hall Effect Hall Effect Inductive Inductive

6. Frequency to Voltage RPM of Router Bit obtained directly RPM of Router Bit obtained directly Sensing material placed on motor axle Sensing material placed on motor axle Sensor generates a pulse as it passes material Sensor generates a pulse as it passes material

7. Frequency to Voltage (cont.) IC converts pulses to frequency IC converts pulses to frequency Frequency is converted to a voltage and sent to micro-controller Frequency is converted to a voltage and sent to micro-controller

8. Current Sensing Devices Detect the current through the motor to determine the motor’s speed Detect the current through the motor to determine the motor’s speed When slip increases, current increases and speed decreases. When slip increases, current increases and speed decreases. Slip is the rotor falling behind the stator Slip is the rotor falling behind the stator

9. Shunt Current Sensing Measures current across a resistor to find the current through the motor.

10. Hall Effect Current Sensing Hall Effect current sensors measure the magnetic fields produced by the current in a power consuming wire

11. Inductive Current Sensing Inductive current sensors work similarly to Hall Effect current sensors

12. Inductive VS Hall Effect

13. Comparison Sensing Method Cost Ease of ImplementationDurabilitySafety Freq. to Voltage $5FairPoorPoor ShuntSensor$4 N/A (DC Only) N/AN/A Hall Effect $25GoodGoodGood Inductive Current $20GreatGreatGreat

14. Final Decision After reviewing each of the methods for sensing current, I determined that the only logical choice was the inductive current sensing method

15. Questions Any questions should be asked now.

16. No Further Questions All questions should have been asked on the previous slide, as the presentation is now over. No birds affected the sensors during the making of this presentation.