1 / 37

E E 1205

E E 1205. Measurements, Data & Accuracy. Measurements. Essential to Engineering Multitude of Sensors Electromagnetic Hall Effect Photonic Simple Yardstick Spring Scales Measuring cups. Measurements. Electrical Conductivity Field Strength Electric Magnetic Frequency/Timing

prince
Download Presentation

E E 1205

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. E E 1205 Measurements, Data & Accuracy

  2. Measurements • Essential to Engineering • Multitude of Sensors • Electromagnetic • Hall Effect • Photonic • Simple • Yardstick • Spring Scales • Measuring cups

  3. Measurements • Electrical • Conductivity • Field Strength • Electric • Magnetic • Frequency/Timing • Voltage • Current • Power/Energy • Luminosity

  4. Representing Data • Significant Digits • 3.14159 (6 sig. digits) • 2.73 (3 sig. digits) • Decimal Places • 3.14159 (5 dec. places) • 0.036 (3 dec. places)

  5. Representing Data • Scientific Notation • 7.382 x 10-8 • -4.690 x 105 • Engineering Notation • 45.2 x 10-6 • -613.8 x 103

  6. Rounding Off Numbers • 52.3691 • 52.369 • 52.37 • 52.4 • 73.85 • 73.8 • 27.55 • 27.6

  7. Excessive Significant Digits • Do not display more significant digits than can be justified • Area calculation: l = 27.4 cm, w = 18.6 cm A = l x w = 510 cm2 , not 509.64

  8. Voltage Divider Circuit

  9. Loaded Voltage Divider

  10. Voltage Divider Equations Unloaded: Loaded: If RL >> R2:

  11. Current Divider Circuit (1/2) If there are only two paths:

  12. Current Divider Circuit (2/2) • In general:

  13. 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

  14. A D’Arsonval Voltmeter

  15. D’Arsonval Voltmeter • Small voltage rating on movement (~50 mV) • Small current rating on movement (~1 mA) • Must use voltage dropping resistor, Rv

  16. Example: 1 Volt F.S. Voltmeter Note: d’Arsonval movement has resistance of 50 W Scale chosen for 1.0 volt full deflection.

  17. Example: 10V F.S. Voltmeter Scale chosen for 10 volts full deflection.

  18. D’Arsonval Ammeter • Small voltage rating on movement (~50 mV) • Small current rating on movement (~1 mA) • Must use current bypass conductor, Ga

  19. Example: 1 Amp F.S. Ammeter Note: d’Arsonval movement has conductance of 0.02 S Ga = 19.98 S has ~50.050 mW resistance. Scale chosen for 1.0 amp full deflection.

  20. Example: 10 Amp F.S. Ammeter Ga = 199.98 S has ~5.0005 mW resistance. Scale chosen for 10 amp full deflection.

  21. 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

  22. Example: Voltage Measurement True Voltage: (If voltmeter removed)

  23. Example: Voltage Measurement Measured Voltage:

  24. Another Voltage Measurement (1/2) True Voltage: (If voltmeter removed)

  25. Another Voltage Measurement (2/2) Measured Voltage:

  26. Example: Current Measurement (1/2) True Current: (If ammeter replaced by short circuit)

  27. Example: Current Measurement (2/2) Measured Current:

  28. Another Current Measurement (1/2) True Current: (If ammeter replaced by short circuit)

  29. Another Current Measurement (2/2) Measured Current:

  30. A Digital Voltmeter • Integrating Converter • Dependent on Vref • Dependent on Temperature • Independent of RC

  31. How the DVM Works

  32. DVM Example If

  33. Measuring Resistance • Indirect • Measure Voltage across Resistor • Measure Current through Resistor • Calculate Resistance (Inaccurate) • d’Arsonval Ohmmeter • Very Simple • Inaccurate • Wheatstone Bridge (Most Accurate)

  34. D’Arsonval Ohmmeter Need to adjust Radj and zero setting each scale change.

  35. Ohmmeter Example 10 mA Full Scale (Outer Numbers) Rb+Radj+Rd’A=150 W Vb=1.5 V Inner (Nonlinear) Scale in Ohms

  36. Wheatstone Bridge Vab= 0 and Iab= 0 Vad = Vbd I1 = I3 I2 = Ix R1I1=R2I2 R3I3=RxIx

  37. Example: Wheatstone Bridge I = 2 A

More Related