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.

Scopes  Time 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.

Scopes  The 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 Scopes  Analog 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.

Waveforms  A 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.

Waveforms  A 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 Cycle  Duty 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 Width  Pulse 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.

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