Oscilloscopes

Oscilloscopes are electrical test instruments that display signal voltages in a two dimensional format providing a visual representation of the signal. The resulting graph uses the vertical (Y) axis to represent voltage and the horizontal (X) axis to represent time. Together, this creates a waveform of the electrical signal making it easy to see how it changes over time.

The characteristics of the waveform provides insightful information on how circuits are performing that cannot be gained from other electrical test tools such as multimeters, including:

• The minimum and maximum voltages of a signal
• The frequency of an oscillating signal
• How a circuit changes a signal as it moves through the circuit
• How frequency or timing of the signal changes over time
• Whether or not a malfunctioning component is distorting the signal
• How much of the signal is noise and whether the noise is changing with time

Uses for Oscilloscopes

Oscilloscopes are one of the most commonly used electrical test instruments. By providing visual representation of an electrical signal, they are indispensable for anyone designing, testing or repairing electronic equipment. Some of the most common applications for oscilloscopes include:

• Power analysis. Oscilloscopes can be used to measure and analyze the operating characteristics of power conversion devices, circuits, and line-power harmonics. Differential amplifier probes are needed to this, and special software is also offered to make analysis of the data easier.
• Serial data analysis. Digital data signals are moving to ever-increasing serial data formats. Oscilloscopes are used to analyze and characterize such data formats as to represent and analyze data formats like USB, Ethernet, Bluetooth, FireWire, and SCSI in addition to many others.
• Jitter analysis. Modern high-bandwidth circuits have incredibly fast clocks and signals. Oscilloscopes are used to represent, analyze, and debug signal jitter as well as timing for clocks, clock-to-data and datastream analysis.
• Data storage device designs can be tested testing by measuring disk performance, media noise and optical recording characteristics.
• Time-domain reflectometry (TDR) is a way to measure impedance values and variations, like faults, along transmission cables, cables connectors or microstrips on a circuit board.

Though most closely associated with testing electrical equipment, oscilloscopes can be used in any application that produces an electrical signal that it can display. Transducers, devices that create an electrical signal in response to physical stimuli, allow oscilloscopes to display nearly any physical phenomena that can be converted into an electrical signal including movement, sound, mechanical stress, pressure, light, or heat. With the right transducer, oscilloscopes can be used to measure brainwaves, heartbeats, engine vibration, voice patterns, and many other things.

Oscilloscope Technology

The earliest method of creating an image of a waveform were oscillograms, hand-drawn representations based on measurements taken with a galvanometer. Later, wave patterns were captured automatically by using a galvanometer to move a pen across a paper drum.

Following the invention of the cathode ray tube (CRT), a type of vacuum tube that uses directed electrons to project images onto a phosphorescent screen, Karl Ferdinand Braun invented the oscilloscope as a physics curiosity in 1897, applying an oscillating signal to electrically charged deflector plates in a phosphor-coated CRT. Many innovations quickly followed. Today’s oscilloscopes are available in a range of form factors and technologies.

In the 1990s, digital technology changed the way oscilloscopes worked. Analog devices, like CRT oscilloscopes, make use of continually varying voltages. Digital oscilloscopes, on the other hand, use binary numbers which correspond to samples of the voltage by using an analog-to-digital converter to change the measured voltages into digital information. Digital oscilloscopes offer a wider range of features and functions and also allow complex processing of the signal by high-speed digital signal processing circuits.

Oscilloscopes typically consist of a display and three basic control sections: Vertical, Horizontal, and Trigger.

The vertical section controls the amplitude of the displayed signal. This section carries a Volts-per-Division (Volts/Div) selector knob, an AC/DC/Ground selector switch and the vertical (primary) input for the instrument.

The horizontal section controls the time base or "sweep" of the instrument. The primary control is the Seconds-per-Division (Sec/Div) selector switch. Also included is a horizontal input for plotting dual X-Y axis signals.

The trigger section controls the start event of the sweep. Several sources can trigger the sweep including any input channel, an external source other than the signal applied to an input channel, the power source signal, or a signal internally generated by the oscilloscope. Oscilloscopes can have several different types of triggers including edge, video, pulse, or logic.

Oscilloscopes also include a range of display controls including focus, intensity, and beam finder as well as input connectors.

Measurements

Wave is a generic term for a pattern that repeats over time. When a wave is represented graphically, it is called a waveform. Oscilloscopes measure voltage signals and display them as waveforms with the vertical (Y) axis representing voltage and the horizontal (X) axis representing time. The shape of the waveform is determined by the characteristics of the signal.

Sine waves are the classic waveform and formed by most AC signals. Square and rectangular waves are the result of signals that turn on and off in regular intervals such as digital signals. Sawtooth and triangular waves are seen in circuits designed to control voltages linearly, like a television, and the transitions change at a constant rate. Transient signals, including steps and pulses, are single-shot signals that indicate a sudden change in voltage. Complex waves combine the characteristics of other wave shapes.

Waveforms can be analyzed for a number of properties including:

• Frequency: The number of times per second a waveform repeats.
• Period: The amount of time it takes for each waveform takes to repeat.
• Duty cycle: The percentage of time that a wave is either positive or negative.
• Rise and fall time: The amount of time it takes for a wave to go from its low point to its high point or from its high point to its low point.
• Amplitude: The measure of how high or low a signal is past 0V. Can sometimes be used as the difference between the high and low voltage points of a signal.
• Maximum and minimum voltages: Displays exactly how high and low the voltage of your signal gets.
• Mean and average voltages: The calculated average of your signal’s minimum and maximum voltage.

Things to Consider When Selecting an Oscilloscope

• How much bandwidth is required?
• What level of accuracy do you need?
• What is an acceptable rise/fall time?
• What probes are needed? Do they match the specifications of the oscilloscope?
• How many channels do you need?
• How fast is the sample rate?
• What type of triggering do you require?
• What is the record length?
• What analytical tools are included?
• Does the software include application support?
• Is connectivity to other devices needed?

If you have any questions regarding oscilloscopes, please don't hesitate to speak with one of our engineers by e-mailing us at sales@instrumart.com or calling 1-800-884-4967.