How to Read a Sine Wave Graph

Waveform and Signal Analysis

Nearly all consumer products today have electronic circuits. Whether a product is simple or complex, if it includes electronic components, the design, verification, and debugging procedure requires an oscilloscope to analyze the numerous electrical signals that make the product come to life.

Understanding oscilloscope basics is critical to almost all product design.

What exactly is an oscilloscope, anyhow? Quite simply, an oscilloscope is a diagnostic instrument that draws a graph of an electrical betoken. This simple graph can tell you many things most a point, such as:

• The time and voltage values of a betoken.
• The frequency of an oscillating indicate.
• The "moving parts" of a circuit represented by the bespeak.
• The frequency with which a particular portion of the bespeak occurs relative to other portions.
• Whether or not a malfunctioning component is distorting the indicate.
• How much of a signal is direct current (DC) or alternating current (Air conditioning).
• How much of the betoken is noise and whether the racket is changing with fourth dimension.

View our complete line of oscilloscopes »

The Oscilloscope's Graph

At the most basic level, an oscilloscope's graph of an electrical signal shows how the point changes over time (Figure 2):

Figure 2: X, Y, and Z components of a displayed waveform.

The intensity or brightness of the display is sometimes called the Z-axis. In Digital Phosphor Oscilloscopes (DPO), the Z-axis can be represented by color grading of the display (Figure iii).

Figure iii:Two offset clock patterns with Z centrality intensity grading.

The Significance of Signal Integrity

A key benefit of an oscilloscope is its ability to accurately reconstruct a signal. The better the reconstruction of the signal the college the betoken integrity. Here's i way to think of indicate integrity. An oscilloscope is analogous to a camera that captures signal images that you and so observe and interpret. Several key issues lie at the heart of point integrity:

• When yous accept a picture, is it an accurate representation of what really happened?
• Is the picture clear or fuzzy?
• How many accurate pictures can you lot take per second?

The dissimilar systems and performance capabilities of an oscilloscope contribute to its ability to deliver the highest signal integrity possible. Probes too impact the betoken integrity of a measurement organisation.

This primer helps you sympathize all of these elements and then y'all can choose and employ the oscilloscope appropriate for your application. Before you lot brainstorm evaluating oscilloscopes, you need to empathize the basics of waveforms and waveform measurements.

This information is covered in this affiliate. It's the foundation of putting an oscilloscope to work for you.

Understanding Waveforms and Waveform Measurements

The generic term for a pattern that repeats over fourth dimension is a wave. Sound waves, brain waves, ocean waves,
and voltage waves are all repetitive patterns. An oscilloscope measures voltage waves. A waveform is a graphic representation of a wave.

Physical phenomena such as vibrations, temperature, or electrical phenomena such as current or ability tin can be converted to a voltage past a sensor. One cycle of a wave is the portion of the moving ridge that repeats. A voltage waveform shows time on the horizontal axis and voltage on the vertical axis.

Waveform shapes reveal a great deal about a signal. Whatsoever fourth dimension you see a change in the height of the waveform, you know the voltage has inverse. Any time there is a flat horizontal line, you know that there is no change for that length of time.

Straight, diagonal lines hateful a linear alter; a ascent or fall of voltage at a steady rate. Sharp angles on a waveform betoken sudden change. Figure iv shows mutual waveforms.

Figure four:Mutual waveforms

Effigy 5 displays sources of common waveforms, such as electrical outlets, computers, automobiles, and televisions.

Figure 5: Sources of common waveforms

Types of Waves

You can classify well-nigh waves into these types:

• Sine waves.
• Foursquare and rectangular waves.
• Sawtooth and triangle waves.
• Step and pulse shapes.
• Periodic and non-periodic signals.
• Synchronous and asynchronous signals.
• Complex waves.

Next we'll look at each of these types of waves.

Sine Waves

The sine moving ridge is the key wave shape for several reasons. It has harmonious mathematical properties"€information technology is the aforementioned sine shape you may have studied in trigonometry class.

The voltage in a wall outlet varies every bit a sine wave. Examination signals produced by the oscillator circuit of a point generator are frequently sine waves.

About Air conditioning power sources produce sine waves (Ac signifies alternating current, although the voltage alternates too; DC stands for direct current, which means a steady current and voltage, such as a bombardment produces.) The damped sine wave is a special instance you lot may see in a circuit that oscillates, but winds downward over time.

Square and Rectangular Waves

The square wave is another common wave shape. Basically, a square wave is a voltage that turns on and off (or goes loftier and depression) at regular intervals. It is a standard wave for testing amplifiers. Skillful amplifiers increase the amplitude of a foursquare moving ridge with minimum distortion.

Television, radio, and computer circuitry often utilize square waves for timing signals. The rectangular moving ridge is like the square wave except that the high and low time intervals are not of equal length. It is particularly of import when analyzing digital circuitry.

Sawtooth and Triangle Waves

Sawtooth and triangle waves outcome from circuits designed to control voltages linearly, such equally the horizontal sweep of an analog oscilloscope or the raster scan of a television receiver.

The transitions between voltage levels of these waves change at a abiding rate. These transitions are chosen ramps.

Step and Pulse Shapes

Signals such equally steps and pulses that occur rarely, or non-periodically, are chosen single-shot or transient signals.

A footstep indicates a sudden modify in voltage, similar to the voltage alter you see if you turn on a power switch.

A pulse indicates sudden changes in voltage, like to the voltage changes you come across if yous turn a power switch on and and so off again. A pulse might represent one chip of information traveling through a computer circuit or it might be a glitch, or defect, in a excursion.

A drove of pulses traveling together creates a pulse train. Digital components in a figurer communicate with each other using pulses. These pulses may be in the form of a series data stream or multiple indicate lines may exist used to represent a value in a parallel data bus. Pulses are also common in x-ray, radar, and communications equipment.

Periodic and Non-periodic Signals

Repetitive signals are referred to as periodic signals, while signals that constantly change are known as non-periodic signals. A still motion picture is analogous to a periodic signal, while a picture show is analogous to a non-periodic signal.

Synchronous and Asynchronous Signals

When a timing relationship exists between two signals, those signals are referred to every bit synchronous. Clock, information, and address signals inside a computer are examples of synchronous signals.

Asynchronous signals are signals between which no timing relationship exists. Because no time correlation exists between the human activity of touching a primal on a computer keyboard and the clock within the estimator, these signals are considered asynchronous.

Complex Waves

Some waveforms combine the characteristics of sines, squares, steps, and pulses to produce complex moving ridge shapes. The signal information may exist embedded in the form of aamplitude, phase, and/or frequency variations.

For example, although the signal in Figure 6 is an ordinary composite video bespeak, it is composed of many cycles of higher-frequency waveforms embedded in a lower-frequency envelope.

In this instance, it is of import to understand the relative levels and timing relationships of the steps. To view this signal, you need an oscilloscope that captures the low-frequency envelope and blends in the higher-frequency waves in an intensity-graded fashion so that y'all can see their overall combination as an epitome y'all tin can interpret visually.

Digital phosphor oscilloscopes (DPOs) are best suited to viewing circuitous waves, such as the video signals shown in Figure 6. Their displays provide the necessary frequency-of-occurrence information, or intensity grading, that is essential to understanding what the waveform is really doing.

Some oscilloscopes can display certain types of complex waveforms in special ways. For example, telecommunication data may be displayed as an eye design or a constellation diagram:

Figure 6: An NTSC composite video betoken is an instance of a complex wave.

Telecommunications digital data signals can be displayed on an oscilloscope as a special blazon of waveform referred to as an heart pattern. The proper name comes from the similarity of the waveform to a serial of eyes (Figure 7).

Center patterns are produced when digital data from a receiver is sampled and applied to the vertical input, while the information rate is used to trigger the horizontal sweep. The middle pattern displays one bit or unit interval of data with all possible border transitions and states superimposed in one comprehensive view.

Figure 7: 622 Mb/due south series data center pattern.

A constellation diagram is a representation of a bespeak modulated past a digital modulation scheme such as quadrature amplitude modulation or phase-shift keying.

Constellation Diagram.

Waveform Measurements

Many terms are used to draw the types of measurements you brand with an oscilloscope. Adjacent nosotros'll expect at some of the well-nigh common measurements and terms.

Frequency and Period

If a betoken repeats, it has a frequency. Frequency is measured in Hertz (Hz) and is the number of times the signal repeats itself in one second. This is also referred to as cycles per 2d.

A repetitive signal also has a menstruum, which is the amount of time it takes the signal to consummate ane cycle.

Menstruation and frequency are reciprocals of each other, so that:

Figure 8: Frequency and catamenia of a sine wave.

Voltage

Voltage is the amount of electric potential, or signal strength, between two points in a circuit. Usually, one of these points is footing, or aught volts, but not ever. You lot may want to measure the voltage from the maximum pinnacle to the minimum acme of a waveform, referred to as the peak-to-summit voltage.

Amplitude

Amplitude is the amount of voltage betwixt ii points in a circuit. Amplitude ordinarily refers to the maximum voltage of a point measured from ground, or cipher volts. The waveform shown in Figure ix has an aamplitude of one V and a acme-to-acme voltage of 2 Five.

Effigy nine: Amplitude and degrees of a sine moving ridge.

Stage

Phase is best explained by looking at a sine wave. The voltage level of sine waves is based on circular motion. Given that a circle has 360°, one cycle of a sine wave has 360°, as shown in Effigy 10.

Using degrees, you tin can refer to the phase bending of a sine wave when yous want to describe how much of the menses has elapsed.

Stage shift describes the deviation in timing betwixt 2 otherwise like signals. The waveform in Figure 10 labeled "current" is said to be 90° out of phase with the waveform labeled "voltage," since the waves attain like points in their cycles exactly 1/4 of a cycle apart (360°/iv = 90°). Phase shifts are common in electronics.

Effigy ten: Stage shift.

Waveform Measurements with Digital Oscilloscopes

Digital oscilloscopes have functions that make waveform measurements easy. They have front-panel buttons and screen-based menus from which yous can select fully-automated measurements. These include amplitude, catamenia, ascent/fall time, and many more than.

Many digital oscilloscopes likewise provide mean and RMS calculations, duty cycle, and other math operations. Automatic measurements appear every bit on-screen alphanumeric readouts. Typically these readings are more authentic than is possible to obtain with direct graticule interpretation.

Examples of fully-automatic waveform measurements

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