1. Rotational Sensors By Erik Flum

2. Types of Sensors Optical Encoder Resolver Rotary Variable Differential Transformer(RVDT) Synchro Rotary Potentiometer

3. History of Encoders 2 types: Absolute or Relative Absolute is made of metal contacts in a binary pattern Relative uses slots and optics

4. Optical Encoder Use either laser or infrared light Use single emitter/receiver for relative Dual emitter/receiver for quadrature 2^n emitter/receiver for absolute Small and cheap $20+

5. Resolver 4+ Inductor coils Analog Encoder Digital Interface 2 Pole resolver for positioning +/-5’ Multi-pole resolver +/-1” Large and expensive $300+

6. RVDT 3 Inductive coils 2 pole rotor / 1 coil on stator Only operate within part of a cycle +/- 45 degrees More common for linear measurement (LVDT) Independent of Frequency, Voltage, Temperature

7. Synchro Powered coil on rotor Y configuration on stator Can be used to move a motor (synchronize movements) Similar construction to AC motor

8. Potentiometer Good linearity Limitation on range of measurement (340-3600 degrees) Accuracy up to 0.005 degrees Sensitive to temperature change Cheap $5+

9. Conclusions Optical encoders: Best accuracy/cost Resolver: Best accuracy RVDT: Best isolated from external effects Potentiometer: Cheapest solution Synchro: Synchronize motors based on position