Todays Agenda More on potentiometers Introduction to AC signals 1 What Potentiometers Look Like: EGR 101 2 Trimmer potentiometers.
EGR 101 3 Potentiometer construction. EGR 101 4 The effect of turning the control shaft on the component resistances.
EGR 101 5 Potentiometer in Multisim Found in Basic category XMM1 R1 Key = A 1kOhm EGR 101
50% 6 R1 XMM1 Key = A 1kOhm 70% Pressing the a key increases percentage
Pressing Shift a decreases percentage EGR 101 7 Note, in Multisim, if you place the potentiometer with the arrow angled down, the resistance will change in the opposite direction XMM1 R1 1K _LIN Key = A
EGR 101 70% 8 R1 Key = A 1kOhm V1 12 V
60% V 12 I 20mA R 600 EGR 101 9 XMM1 R1 Key = A
1kOhm V1 12 V EGR 101 60% 10 Information on Lamps in Multisim
The lamp youll need for the prelab can be found under Indicators/Virtual_Lamp EGR 101 11 11 Chapter 9 Alternating Current DC & AC Circuits 12 DC: Direct Current
A DC current is a current that does not change direction in time. 13 Example of DC circuits: Portable flashlight circuit. Internal circuit inside a DMM to measure resistance. Circuit to control a dimmer light using a potentiometer, as you will on Thursday.
EGR 101 14 14 AC: Alternating Current An AC current is a current that changes direction in time. 15 Imagine you take a battery with one polarity between
times t0 and t1 (top schematic). Flip polarity between t1 & t2 (bottom schematic). EGR 101 16 16
Flipping batteries is unrealistic. However, you can built an AC circuit using two batteries and a SPDT switch, as shown below. When the switch is flipped to the right you get +15 V. When the switch is flipped to the left you get -15 V. V2 V1 15 V 15 V
J1 Key = Space EGR 101 17 17 In-Class Activity 1
Working in pairs, simulate the circuit below in Multisim. The single pole, double throw (SPDT) switch can be found in the Basic, switch category. Flip the SPDT switch using the space key and watch how the meter reading alternates between +15 V and -15 V. EGR 101 18 18 Oscilloscope piece of equipment that provides
a visual representation of a voltage waveform EGR 101 19 19 In-Class Activity 2 Repeat simulation using an oscilloscope (4th instrument down on right column). Watch on the scope how fast the voltage alternates: click the space bar slowly. (see slide 21)
click the space bar fast. (see slide 22) EGR 101 20 20 Slow Clicks (Low Frequency AC) EGR 101 21 21
Fast Clicks (High Frequency AC) EGR 101 22 22 AC using 555 timer Although you can easily create the previous AC circuit using two batteries and SPDT, you can automate the circuit using a 555 timer, as you are going to do in your semester projects, as shown in the next slide.
EGR 101 23 23 Switching between two batteries automated using 555 timer 555 timer SPDT replaced with Relay
two batteries EGR 101 24 24 How do we characterize the differences in the waveforms we generated? For periodic rectangular waves:
Insert Figure 9.39 EGR 101 25 25 Rectangular Waves - Terminology and Time Measurements EGR 101
26 26 Rectangular Waves - Duty Cycle ratio of pulse width to cycle time PW duty cycle (%) X 100 T where PW = the pulse width of the circuit input
T = the cycle time of the circuit input EGR 101 27 27 In-Class Activity 3 For the following waveforms, specify the pulse width, space width and period: a)
2 ms 5 ms 10 ms EGR 101 28 One of the most important AC signals is the periodic sinusoid, as shown below.
Power generation power plants. Design of radios and radio stations. EGR 101 29 29 Difference between AC & DC
Demo. Loss of DC power over long distance. AC power transport is more efficient. http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html EGR 101 30 30
Generating a Sine Wave EGR 101 31 31 EGR 101 32 32
Alternations and Cycles Alternations the positive and negative transitions Cycle the complete transition through one positive alternation and one negative alternation Half-Cycle one alternation Insert Figure 9.3
EGR 101 33 33 Cycle Time (Period) The time required to complete one cycle of a signal ms T 4 div 5
20 ms div EGR 101 34 34 In-Class Activity 4 Calculate T in ms Calculate T in ms EGR 101
35 35 Frequency the rate at which the cycles repeat themselves Unit of Measure Hertz (Hz) = cycles/second T = 200 ms = 0.2s f = 1/0.2 = 5 cps
= 5 Hz EGR 101 36 36 Relation between Cycle Time (Period) and Frequency 1 f T
or 1 T f where T = the cycle time (period) of the waveform in seconds Another way to describe periodicity of the wave is through the angular frequency defined as 2 f where = angular velocity, in radians per second
2 = the number of radians in one cycle f = the number of cycles per second (frequency) EGR 101 37 37 Note that same thing as
What is a radian? is not the 1 [ f ] Hz s rad [ ] s EGR 101
38 38 1 Radian the angle formed within a circle by two radii separated by an arc of length equal to the radii ra 1 rad r1 when ra = r1
EGR 101 39 39 Instantaneous Value the value of a sinusoidal voltage or current at a specified point in time can be expressed as: v(t ) V pk sin(t ) where Vpk is the magnitude of the voltage.
In terms of f, v(t ) V pk sin(2ft ) EGR 101 40 40 In-Class Activity 5 An AC voltage in volts is given by v(t ) 10 sin(377t )
what is the unit of the number 10? what is the unit of the number 377? what is the angular frequency in rad/s? what is the frequency in Hz or cps? what is the period in ms? EGR 101
41 41 In-Class Activity 5 A device emits a sinusoidal signal that has a magnitude of 1 volt and a frequency of 690 kHz. what is the angular frequency in rad/s? what is the period in ms? Express this signal as v(t ) A sin(t ) (i.e. fill in the values
for A and ) Express this signal as v(t ) A sin(2ft ) EGR 101 42
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