1. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 EE 1106 : Introduction to EE Freshman Practicum Lecture 3: Measurements, Precision Credit: Dr. Bill Dillon, EE Dept., UTA

2. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Measurements Essential to Engineering Multitude of Sensors –Electromagnetic –Hall Effect –Photonic –Simple Yardstick Spring Scales Measuring cups

3. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Measurement Accuracy and Precision

4. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Measurement Errors Inherent Instrument Error Poor Calibration Improper Use of Instrument Application of Instrument Changes What was to be Measured –Ideal Voltmeters have Infinite Resistance –Ideal Ammeters have Zero Resistance

5. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Measuring Resistance Indirect –Measure Voltage across Resistor –Measure Current through Resistor –Calculate Resistance (Inaccurate) d’Arsonval Ohmmeter –Very Simple –Inaccurate Wheatstone Bridge (Most Accurate)

6. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 D’Arsonval Meter Movement Permanent Magnet Frame Torque on rotor proportional to coil current Restraint spring opposes electric torque Angular deflection of indicator proportional to rotor coil current

7. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 D’Arsonval Ohmmeter Need to adjust R adj and zero setting each scale change.

8. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Ohmmeter Example 10 mA Full Scale (Outer Numbers) R b +R adj +R d’A =150  V b =1.5 V Inner (Nonlinear) Scale in Ohms

9. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Measuring Voltage and Current

10. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 A Digital Voltmeter Integrating Converter Dependent on V ref Dependent on Time Independent of RC

11. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 How the DVM Works

12. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 DVM Example

13. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Calculating Resistance When conductor has uniform cross-section

14. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Temperature Coefficient of Resistance Metallic conductors have a linear increase of resistance with increased temperature. T o is the reference temperature (usually 20 o C) and R o is the resistance at the reference temperature.  is the temperature coefficient of resistance for the material. At 20 o C, some values for  are: MaterialAlpha @ 20 o C Aluminum0.004308 Copper0.004041

15. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Color Coding of Resistors http://www.csgnetwork.com/resistcolcalc.html

16. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Resistor Measurements on Breadboard

17. Dan O. Popa, Intro to EE, Freshman Practicum, Spring 2015 Prelab 4 due next class!! Available online at course website Acknowledgements: Dr. Bill Dillon, and NI Labview 3 hour courseware Questions? 17