BASICS OF LAB SCOPES

Scope Essentials Digital Storage Oscilliscope (DSO) Voltmeter that captures voltage samples & displays them on a screen Voltage appears as a trace of light Trace moves up & down, displaying voltage Trace moves left to right, displaying time Digital Multimeters (DMM) take slower samples, displays them as a numeric value

Scope Essentials DSO takes rapid fire samples (snapshots) of voltage Samples are digitized & displayed on screen These digitized samples can be saved for future use or transferred to a computer

The Waveform Waveform – the line traced on the screen Scopes show voltage levels over a period of time (horizontal) Amplitude – difference between a signals lowest and highest value (0 – 5v) (vertical) Frequency – rate at which a signal repeats itself in one second, measured in Hertz

Waveform Shape Signature of the voltage signal When measuring sensors, each has it’s own unique shape

The Scope Screen Divided into small sections - Grids 8 x 10 grid Screen Voltage level between grids is adjustable Time base between grids is adjustable

Voltage & Time Divisions

Trigger Voltage level that the sampled signal must cross to start the horizontal sweep that draws the waveform across the screen If voltage level is 2v set trigger at 1v

Trigger & Slope Trigger sets the voltage level that the signal must cross to start a sweep Positive slope – triggers the sweep on a rising voltage Negative slope – triggers the sweep on a falling voltage

Coupling Describes the type of signal being sampled DC coupling – for use with direct current circuits ( any unwanted AC voltage will be displayed) AC coupling – for use with alternating current ( blocks DC voltage)

AC Coupling Sensor location

DC Coupling

Pulse Width Modulated Signals Controlled switching of voltage on & off Fig. A – total cycle time is 35ms –Injector is off 23ms –Injector is on 12ms Fig. B – –Injector is off 13ms –Injector in on 22ms

Pulse Width Modulated Signals PWM values can be shown in milliseconds or as a percentage

Glitch Intermittent malfunction in either a circuit or a component Sudden change in voltage