Lecture 2 - Series Circuits and Electrical Measurements PDF

IM 115 Introduction to Series Circuits and Electrical Measurements Terms & Definitions Direct current (dc) – current that flows in only one direction Alternating current (ac) – current that flows in one direction, then the other Source – a device that supplies voltage pressure & current...

IM 115 Introduction to Series Circuits and Electrical Measurements Terms & Definitions Direct current (dc) – current that flows in only one direction Alternating current (ac) – current that flows in one direction, then the other Source – a device that supplies voltage pressure & current flow to a circuit Switch – a control device that either prevents or allows the flow of current Terms & Definitions Open circuit – a circuit that does not have a complete path for current flow Closed circuit – a circuit that has a complete current path Continuity – an uninterrupted path for electrical current Short circuit – an unwanted path of current flow Essential circuit components, Series Circuits and Electrical Measurements Objectives: List all four components necessary for an electric circuit and understand their function Be able to discuss the concepts of a series circuit Understand and be able to make the three basic measurements in an electrical circuit. Resistance, Voltage and Current  The four components Power Source Conductors Switch Loads The power source Power sources must be large enough to accommodate the loads connected to it Voltages vary:  1.5 Vdc  24 Vac  110/120 Vac  208/230 Vac  460/480 Vac  Higher… Single or Three phase  Most industrial equipment is 3 phase (3 Ø) The four components Conductors Carries current to each part of the circuit Must be sized and selected correctly for current and voltage Switches  Manual switches  Equipment disconnect switches  Light switches  Automatic switches  Motion detectors  Pressure operated switches  Temperature operated switches Switches  1, 2 or 3 poles  Depends on the voltage and phases  1 pole switches are for 110/120 VAC single phase  2 pole switches are for 208/230 VAC single phase  3 pole switches are for all three phase power supplies  Ratings:  Maximum voltage  Maximum current  Example: 15 Amps @ 250 VAC  Manual or automatic switches Switches Characterized by the number of poles and throws Poles: the number of paths current could potentially take Throw: the number of ways a switch can be directed in order to close SPST SPDT DPST NOPB NCPB Single-Pole rotary Loads The part of an electric circuit that uses the power sent by the source, switch(es) and conductors Many types Motors Heater elements Resistors Coils Lights Loads Several ratings are common to all loads Voltage – Must be followed precisely Phases – Must be followed precisely Watts – The amount of power it consumes in a given time All loads contain some electrical resistance Absence of a load creates an electrical short circuit Protective Devices add safety A fuse or circuit breaker opens the circuit when a set current is exceeded a blown fuse must be replaced an open circuit breaker may be reset Circuit Fuse Breaker The Electrical Schematic Control Device Voltage 12 V Load 10 k Source Protective Device The Electrical Schematic Control Device Voltage 12 V Load 10 k Source Protective Device Figure 2-36 An example of an SPDT switch controlling two lamps. Thomas L. Floyd Copyright ©2003 by Pearson Education, Inc. Principles of Electric Circuits, 7ed. Upper Saddle River, New Jersey 07458 All rights reserved. What is a Series Circuit? one path for current flow basically we are talking about a single pipe carrying electrons current is the same at all points What is a Series Circuit? A series circuit is a circuit that requires that all current flow from the source flow through one path and all components in that particular circuit Voltage in a series circuit Series Circuit Rule #1 – Voltage always divides in a series circuit. It will share some of the voltage over each load according to each loads resistive value. Current in a Series Circuit Current is just like water in pipe if you are pumping X gal per min thru one part of the pipe, you have got X gal per min going thru the entire length of the pipe Series Circuit Rule #2. Current is always the same when measured anywhere in a series circuit or branch. If you put two ammeters in different points of a series circuit they will both read the same You always have the same amount of current coming out of the end of a series circuit as is going in Resistors in Series If we add one (or more) resistors in series as we may expect, the total resistance goes up As we add additional resistors, the total resistance continually goes up Series Circuit Rule #3 - Resistors in add straight up Resistors in series add algebraically e.g. a 20 in series with a 20 have 40  of resistance The addition of resistance in series holds whether you have 2 resistors or 100 Resistors in Series For the total resistance of the circuit it doesn't matter what order the resistors are in  you can move the resistors around as long as they remain in the circuit, in series the total or series resistance will remain the same Resistors in Series 10  10  10  10  10  Rtotal= 5  10Ω = 50  Resistors in Series 3.4k 1.1k 5.6k Rtotal=3.4 k + 1.1 k  + 5.6 k = 10.1 k 5.6k 3.4k 1.1k Rtotal=5.6 k + 3.4 k  + 1.1 k  = 10.1 k Using Electrical Meters Meters Analog Digital Multimeter (VOM) Meters Analog Meter movement Current magnetic field  Multimeter (VOM) Meters Range switches Range readings Resistance Ohms adjust Zero adjust  Meters Digital Electronic Digital Multi Meter (DMM) Ground Term originated from power companies practice of tying one side of power line to a metal rod driven into the ground termed – earth ground other common grounds – chassis and circuit ground Common Schematic symbols for ground Basic Circuit Measurements Measuring current with an Ammeter to measure current all the current must go through the ammeter A VS R Current Measurements Basic Circuit Measurements Measuring voltage with a Voltmeter voltage measurements are a comparison of the voltage potential at two points in the circuit VS R V Voltage Measurements Basic Circuit Measurements Measuring resistance with an Ohmmeter no power must be on the circuit component must be removed or disconnected to insure only one path is available VS R  Resistance Measurements