Scopes

An oscilloscope is a visual voltmeter.An oscilloscope converts electrical signals into a visual image representing voltage changes over a specific period of time.

Scopes

The information is is displayed in the form of a continuous voltage line called a waveform pattern or trace.

An oscilloscope screen is a cathode ray tube (CRT), which is very similar to the picture tube in a television set.

Scopes

An upward movement of the voltage trace on an oscilloscope screen indicates an increase in voltage, and a downward movement of this trace represents a decrease in voltage.

The size and clarity of the displayed waveform is dependent on the voltage scale and the time reference selected by the technician.

Scopes

Dual-trace oscilloscopes can display two different waveform patterns at the same time.

The screen of a lab scope is divided into small divisions of time and voltage.

These divisions set up a grid pattern on the screen.

ScopesTime is represented by the horizontal

movement of the waveform.Voltage is measured is measured with the

vertical position of the waveform.The scope displays voltage over time.The waveform moves from the left to the

right.The value of the divisions can be adjusted to

improve the view of the voltage waveform.

ScopesThe scope display is divided into small

sections. A series of grids, or graticules divide the display.

The voltage level between grids is adjustable

e.g. - If the signal ranged between zero and one volt, five volts per division would be too high.

Analog vs Digital ScopesAnalog scopes show the actual activity

of a circuit and are called real-time scopes.

A digital scope, (DSO) digital storage oscilloscope, converts the voltage signal into digital information and stores it in its memory.

A technician can freeze the captured signal for close analysis.

Scopes

Both an analog and a digital scope can be dual-trace scopes.

By watching two traces simultaneously, you can watch the cause and effect of a sensor, as well as compare a good or normal waveform to the one being displayed.

WaveformsA waveform represents voltage over

time.When the trace is a straight horizontal

line, the voltage is constant.A diagonal line up or down represents

an increase or decrease in voltage.Scopes can display AC or DC voltage,

either one at a time or both at the same time.

WaveformsA normal AC signal changes its polarity

and amplitude over a period of time.The waveform created by AC voltage is

called a sine wave.One complete sine wave shows the

voltage moving from zero to its positive peak, then moving down through zero to its negative peak and returning to zero.

One complete sine wave is a cycle.

Waveforms A complete cycle is the amount of time a

signal takes before it begins to repeat itself. The number of cycles that occur per second

is the frequency of the signal. Square waves are identified by having

straight vertical sides and a flat top. This type of wave represents voltage being

applied, voltage being maintained, and no voltage applied.

Pulse Train

A pulse train is any electrical signal that turns on and off, or goes high and low, in a series of pulses.

Pulse train signals can vary in three ways.

Frequency

Frequency is the number of cycles that take place per second.

The more cycles that take place in one second, the higher the frequency reading.

Frequencies are measured in Hertz, which is the number of cycles per second.

An eight Hertz signal cycles eight times per second.

Duty CycleDuty cycle is a measurement comparing the

signal on-time to the length of one complete cycle.

Duty cycle is measured in percentage of on-time.

A 60% duty cycle is a signal that’s on 60% of the time, and off 40% of the time.

Dwell is another way of measuring duty cycle. Measured in degrees instead of percent.

Pulse WidthPulse width is the actual on time of a

signal, measured in milliseconds.With pulse width measurements, off-

time doesn’t really matter - the only real concern is how long the signal’s on.

In automotive applications, the only type of signal we measure signal pulse width is electronic fuel injectors.

E.G. - ABS brake sensor With the pickup disconnected: Connect one probe to

one of the leads from the coil, and the other probe to the other lead.

Voltage scale: 200 mVAC Time Base: 5 ms - up, depending on speed Trigger: Level: zero volts Slope:

positive The wheels must turn for the ABS sensors to produce

a waveform. Signal frequency increases with vehicle speed.

Pronoun and Antecedent Agreement

Agreement in person The resident made her feelings known.

Agreement in number The residents made their feelings known. The board of directors gave its approval.

(the board acted as a single unit.) Some of the creditors have expressed concern Some of the gasoline has water in it.

Agreement in gender A manager must use his or her judgment.

The End