Electric Curcuits and Measurements

Basic Electrical components and their functions

Measurements of electrical circuits characteristics

- Multimeter - Oscilloscope - Function Generator

Building Curcuits From Schematics Basic Electrical components: - resistors - capacitors - Potentiometers - Capacitors - Diodes - LED’s (light emitting diodes)

Electronic Circuit is a collection of components that electricity is driven through to accomplish a task

wire has no resistance

Building Curcuits From Schematics breadboard is a

plastic matrix with holes

Power supply and ground

Leads of el. components are inserted into the holes

Bus strips holes are electrically connected in vertical direction (used for power distribution)

terminal strips holes are electrically connected in horizontal direction (5 holes series only)

Resistors Resistor – dissipative element that converts

electrical energy into heat. Ohm’s law V=IR Defined by voltage-current characteristics –

slop of the voltage-current curve:

Wire-lead resistor’s value and precision are coded with four colored bands

Bands: a – tens digit, b – ones digit, c- power of 10, tol – tolerance of uncertainty

Resistors

Example: a = green, b=brown, c= red, and t= tol = gold

Range of possible resistance values:

%10 toleranceabR c

OhmROhmOhm

OhmR

53004800)510005.0(5100

%51051 2

Resistors in series: R=R1+R2Resistors in parallel: R=R1*R2/(R1+R2)

Resistors Kirhchoff’s Laws: - Sum of voltages around a closed

loop or path is zero:

- Sum of currents flowing into a

surface or node is zero:

01

N

iiV

01

N

iiI

Series Resistors Curcuit Voltage divider - voltage Vs divides between each resistor - creates different reference voltages in a

circuit (having single output supply)

VRR

seq

iRV 1

Resistors/Potentiometer

Potentiometer or pot – variable resistor

Provide range of resistance values controlled by mechanical screw, knob or linear slide:

Capacitor Capacitor is a passive element that stores

energy in the form of an electric field (as a result of a separation electric charge)

Consists of conducted plates separated by dielectric material

Capacitance (C) units: farads

Dielectric material is an insulator that increases the capacitance as a result of permanent or induced electric dipoles in the material

Capacitor Capacitors in parallel

C = C1+C2

Capacitors in series:

C = C1*C2/(C1+C2)

Diodes Diode is a pn-junction that passes current

in only one direction (or rectifier)

Analog to check valve

Diodes

Optoelectronic Diodes or Light Emitting Diodes (LEDs) – emit photons

- positive lead (anode) is longer

Measurements

Multimeter (measurements in DC circuits)

Oscilloscope (measurements in AC/DC circuits

Function generator (power supply for generation of

voltage waveform)

Measurements/Multimeters

Multimeter (measurements in DC circuits)

-Only measure resistance when power to the circuit is OFF ;

- during resistance or voltage measurements multimeter probes are place in parallel to the circuit;

- in current measurement the probes need to be placed in series (you need to disconnect the el. component)

Measurements/ OscilloscopeOscilloscope – voltage-measuring instrument, capable of recording high frequency signals (chapter 3.5.4, p. 10 of manual)

Measurements/ OscilloscopeBasic concepts (see course web-page) Probe Self-calibration Triggering - determines proper acquirement of data - options (source, coupling etc.) Acquiring Data Scaling and Positioning Waveforms - vertical, horizontal - aliasing etc… Autoset Math functions Etc…

Measurements/ Oscilloscope/Triggering To ensure that a recording of the signal

from the transducer is made at a correct time (or synchronized) triggering is used

(see details in manual, p.10) Triggering synchronizes an oscilloscope

with the event (signal capturing)

Sources of trigger signals: - input channel (commonly used) - AC Line - External Input channel triggering: - uses input signal, activate internal

sawtooth generator and initiate synchronization;

- frequency of the generator is adjusted to the one of the input signal

- signal trace appears stationary on the screen

Measurements/ Oscilloscope/Triggering

Auto triggering: depends on time-base (controlled by SEC/DIV knob)

Time base (p.16, manual) – controls how often the values (of a signal) are digitized

Measurements/ Oscilloscope/Scaling and positioning waveforms

You can change size, scale and position of the wave form on the display (vertically and horizontally, using SEC/DIV knob)

Aliasing – occurs when the oscilloscope does not sample signal fast enough (check it using SEC/DIV knob)

Measurements/ Oscilloscope/Menu Control buttons

SAVE/RECALL – restore factory settings

Measurements/ Oscilloscope Taking measurements (p.37-39,

manual)

- using autoset (when signal amplitude or frequency unknown)

- automatic measurements - two signals measurements: