Lect-01-ElectrMaterials

Lect-01-ElectrMaterials - ME ­340 Circuits &...

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Unformatted text preview: ME ­340 Circuits & Mechatronics Lecture # 01 The University of Texas at Aus?n Mechanical Engineering Department ME-340 (Introduction to) Mechatronics SI Units (Basic 7) 2 ME-340 (Introduction to) Mechatronics Electricity: microscopic view –  Inside atoms are •  Electrons (nega.vely charged) •  Neutrons (neutral) •  Protons (posi.vely charged) –  Forces •  Similar repel •  Different aPract –  Electricity from charge 3 ME-340 (Introduction to) Mechatronics Charge, Voltage & Current •  Charge q [coulombs-C] •  Voltage V [volts-V = J C-1]: difference of electric potential, or Work [joules-J] per charge W V= q •  Current i [Amperes – A = C s-1]: charges in motion, or flow of charge per unit time. € dq (t ) Δq i (t ) = ≈ dt Δt 4 ME-340 (Introduction to) Mechatronics € Direc?on & Charge Conven?ons •  Voltage: POLARITY marker ( ± or red & black), indicates difference in energy. •  DIRECTION of current flow (+ to  ­) determines polarity •  Current Flow: flow rate of charge carriers (electrons, ions, holes, etc.) 5 ME-340 (Introduction to) Mechatronics Schema?c Diagram & Elements Sample of Component Library System Schematic 6 ME-340 (Introduction to) Mechatronics Electrical Materials •  Atomic structure affects charge flow •  Materials: –  Conductors: charge flows easily •  Electrons jump easily from atom to atom •  Copper, Gold, Aluminum, Silver, etc. –  Insulators: do not conduct •  electrons ?ghtly bound to atom •  Porcelain, Plas?c, Rubber, Glass, etc. –  Semiconductors: conduc?vity in between •  Silicon, Phosphorous, Arsenic, Germanium, etc. 7 ME-340 (Introduction to) Mechatronics Currents + - Positive charge moving across area in reference direction ⇒ positive current. If opposite, negative. ∂q(t ) Δq i( t ) = ≈ ∂t Δt 8 ME-340 (Introduction to) Mechatronics •  Ben Franklin: charge carriers positive, flow directed along current + ⊕→ - •  Reality: charges usually negative electrons, flow opposite to current + e← •  Both give same current direction! ME-340 (Introduction to) Mechatronics - 9   Select (arbitrarily) reference direction of currents   If (after solving circuit) current is negative, flow in opposite direction 10 ME-340 (Introduction to) Mechatronics 11 Currents (Double Subscript) •  Arrow: direc?on of current (+ charges) •  Double subscript: current flow from node to node •  Opposite nega?ve (charge or direc?on) iab = −iba ME-340 (Introduction to) Mechatronics Voltages (charges uphill) (charges downhill) 12 ME-340 (Introduction to) Mechatronics •  Assign voltages, choosing reference polarities arbitrarily 13 ME-340 (Introduction to) Mechatronics 14 Voltage (Electric Poten?al) •  Poten?al between nodes: + polarity @ head of arrow •  Double subscripts: –  vab posi?ve from (a) to (b) –  reverse: vba =  ­ vab υ ab = −υ ba ME-340 (Introduction to) Mechatronics Waveforms 15 ME-340 (Introduction to) Mechatronics 16 Circuit Elements •  Voltage or current “applied”, element “responds” with other (current or voltage) •  Elements: –  Sources: Voltage & Current –  Energy Storage: Capacitor & Inductor –  Power Dissipa?on: Resistors/ Conductors P =υ ⋅i ME-340 (Introduction to) Mechatronics 17 Power •  Power (W): rate of change of energy P ( t ) = υ ( t ) ⋅ i( t ) •  i from + to  ­, posi?ve charges go “downhill”, element “passive”. P = v i > 0, element absorbs power •  i from – to +, posi?ve charges go “uphill”, element “ac?ve”. P = v i < 0, element gives power ME-340 (Introduction to) Mechatronics Example 1.2 (Power Calcula?ons) 24W absorbed 12 W supplied 36 W supplied 18 ME-340 (Introduction to) Mechatronics Next Class •  Introduc?on to Electrical Circuits –  Signals (Voltage, Current, Charge, etc.) –  Elements (Sources, Resistor, Capacitor, etc.) –  Circuits (Series, Parallel, etc.) 19 ME-340 (Introduction to) Mechatronics ...
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This document was uploaded on 02/14/2012.

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