Oscilloscope Tutorial.ppt

8/10/2019 Oscilloscope Tutorial.ppt

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Oscilloscope Tutorial

The oscilloscope is basically a graph-

displaying device

It draws a graph of an electrical signal.

In most applications the graph shows how

signals change over time:

the vertical (Y) axis represents voltage

the horizontal (X) axis represents time.


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Oscilloscopes

Horizontal sweeps at a constant rate. Vertical plates are

attached to an external voltage, the signal you attach to the

scope.


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Cathode Ray Tubes

Variation in potential difference (voltage)

placed on plates causes electron beam to

bend different amounts.

Sweep refers to refreshing repeatedly at a

fixed rate.


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Scope (Cont)

This simple graph can tell you many things about a signal: You can determine the time and voltage values of a signal.

You can calculate the frequency of an oscillating signal.

You can see the "moving parts" of a circuit represented by thesignal.

You can tell if a malfunctioning component is distorting the signal.

You can find out how much of a signal is direct current (DC) oralternating current (AC).

You can tell how much of the signal is noise and whether the noiseis changing with time.


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How does an Analog Scope work?


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How does a Digital Scope work?


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Triggering Stabilizes a Repeating Waveform


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Waveform shapes tell you a great deal about a signal


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Voltage, Current, & Phase


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Performance Terms

Bandwidth

The bandwidth specification tells you the frequency range the oscilloscope accurately measures.

Rise Time

Rise time may be a more appropriate performance consideration when you expect to measure pulsesand steps. An oscilloscope cannot accurately display pulses with rise times faster than the specified

rise time of the oscilloscope. Vertical Sensitivity

The vertical sensitivity indicates how much the vertical amplifier can amplify a weak signal. Verticalsensitivity is usually given in millivolts (mV) per division.

Sweep Speed

For analog oscilloscopes, this specification indicates how fast the trace can sweep across the screen,allowing you to see fine details. The fastest sweep speed of an oscilloscope is usually given innanoseconds/div.

Gain Accuracy The gain accuracy indicates how accurately the vertical system attenuates or amplifies a signal.

Time Base or Horizontal Accuracy

The time base or horizontal accuracy indicates how accurately the horizontal system displays thetiming of a signal.

Sample Rate

On digital oscilloscopes, the sampling rate indicates how many samples per second the ADCcanacquire. Maximum sample rates are usually given in megasamples per second (MS/s). The faster the

oscilloscope can sample, the more accurately it can represent fine details in a fast signal.. ADC Resolution (Or Vertical Resolution)

The resolution, in bits, of the ADC indicates how precisely it can turn input voltages into digitalvalues.

Record Length

The record length of a digital oscilloscope indicates how many waveform points the oscilloscope isable to acquire for one waveform record.


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Grounding Proper grounding is an important step when setting up to take

measurements.

Properly grounding the oscilloscope protects you from a hazardous shockand protects your circuits from damage.

Grounding the oscilloscope is necessary for safety. If a high voltagecontacts the case of an ungrounded oscilloscope, any part of the case,including knobs that appear insulated, it can give you a shock. However,with a properly grounded oscilloscope, the current travels through the

grounding path to earth ground rather than throughyouto earth ground. To ground the oscilloscope means to connect it to an electrically neutralreference point (such as earth ground). Ground your oscilloscope by

plugging its three-pronged power cord into an outlet grounded to earthground.

Grounding is also necessary for taking accurate measurements with your

oscilloscope. The oscilloscope needs to share the same ground as anycircuits you are testing.

Some oscilloscopes do not require the separate connection to earth ground.These oscilloscopes have insulated cases and controls, which keeps any

possible shock hazard away from the user.


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Scope Probes

Most passive probes have some degree of attenuation factor, such as 10X,

100X, and so on. By convention, attenuation factors, such as for the 10X

attenuator probe, have the X after the factor.In contrast, magnification factors like X10 have the X first


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Vertical Controls

Position and Volts per Division

The vertical position control lets you move thewaveform up or down to exactly where you want it on

the screen.

The volts per division (usually written volts/div) settingvaries the size of the waveform on the screen.A goodgeneral purpose oscilloscope can accurately display

signal levels from about 4 millivolts to 40 volts. Often the volts/div scale has either a variable gain or afine gain control for scaling a displayed signal to acertain number of divisions.


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Input Coupling

Coupling means the method used to connect an

electrical signal from one circuit to another.


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Horizontal Controls

Position and Seconds per Division The horizontal position control moves the waveform

from left and right to exactly where you want it on the

screen. The seconds per division (usually written as sec/div)

setting lets you select the rate at which the waveform isdrawn across the screen (also known as the time basesetting or sweep speed). This setting is a scale factor.

For example, if the setting is 1 ms, each horizontaldivision represents 1 ms and the total screen widthrepresents 10 ms (ten divisions). Changing the sec/divsetting lets you look at longer or shorter time intervalsof the input signal.


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Trigger Position

The trigger position control may be located in the horizontal control section ofyour oscilloscope. It actually represents "the horizontalposition of the triggerin the waveform record." Horizontal trigger position control is only availableon digital oscilloscopes.

Varying the horizontal trigger position allows you to capture what a signal didbeforea trigger event (calledpretrigger viewing).

Digital oscilloscopes can provide pretrigger viewing because they constantlyprocess the input signal whether a trigger has been received or not. A steadystream of data flows through the oscilloscope; the trigger merely tells the

oscilloscope to save the present data in memory. I

n contrast, analog oscilloscopes only display the signal after receiving thetrigger.


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Trigger Controls (cont)


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Pulse and Rise Time Measurements


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Multimeter tutorial

A meter is a measuring instrument. An

ammetermeasures current, a voltmeter

measures the potential difference (voltage)between two points, and an ohmmeter

measures resistance.

A multimetercombines these functions,and possibly some additional ones as well,

into a single instrument.


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To measure current, the circuit must be broken to allow

the

ammeter to be connected in series

Ammeters must have a LOW resistance


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To measure potential difference (voltage), the circuit is

not changed: the voltmeter is connected in parallel

Voltmeters must have a HIGH resistance


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To measure resistance, the component must be

removed from the circuit altogether

Ohmmeters work by passing a current through thecomponent being tested


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Digital Multimeters

Digital meters give an output in numbers, usually on a liquid

crystal display.

Most modern multimeters are digital and traditional analogue

types are destined to become obsolete.

Digital multimeters come in a wide range of sizes and

capability. Everything from simple 3 digit auto ranging

pocket meters to larger 8 digit bench model with operatoror computer (IEEE488 compatible) settable range selection


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Function Generator

An electronic instrument that generatesvarious waveforms such as

Sine waveSquare wave

Pulse trains

Sawtooth

The amplitude, DC offset, frequency areadjustable.


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Function Generators (cont)

Like multimeters there is a wide variety of

device offering various

Amplitude characteristics

Bandwidth

Adjustments of rise and fall times

Modulation capability (AM, FM, Pulse, etc.)


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Power Supply

This is the device that transfers electric power from asource to a load using electronic circuits.

Typical application of power supplies is to convert utility'sAC input power to a regulated voltage(s) required forelectronic equipment.

Depending on the mode of operation of powersemiconductors PS can be linear or switching.

In a switched-mode power supply, or SMPSpowerhandling electronic components are continuously switching

on and off with high frequency in order to provide thetransfer of electric energy. By varying duty cycle,frequency or a phase of these transitions an output

parameter (such as output voltage) is controlled. Typicalfrequency range of SMPS is from 20 kHz to several MHz.


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Power Supply (cont)

Power supplies like many of the other electronicinstruments, come in many varieties with a widerange of capabilities:

Parameters that are Power Supply specific include:

Voltage levels Current

Regulation

Protection

Output impedanceNoise (ripple)

Its the designer (or researcher) responsibility toidentify the characteristics required.


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Oscilloscope


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Oscilloscope(continue)

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Oscilloscope Tutorial.ppt