What are Oscilloscopes?

Carol Francois

Oscilloscopes are electronic testing machines that are used to display signal voltages as a function of time on a screen. The screen provides a two-dimensional graph of the electrical potential differences along the vertical axis and time or another voltage along the horizontal axis. These machines are also known as scopes or O-scopes, and are among the most widely used electronic tools.

Oscilloscopes are used to measure the change in an electrical signal over time.
Oscilloscopes are used to measure the change in an electrical signal over time.

Used in medicine, engineering, telecommunications, science, and other technology-based industries, oscilloscopes are designed to measure the frequency and amplitude of an electrical signal. They provide a clear view of the exact wave shape of the signal, and show distortion and the timing of the waves for two related signals. A well-known tool, they are easy to use and understand for anyone who has studied electricity wave patterns.

Coaxial cable is commonly associated with cable TV installation, but is also used for specialized computers and other equipment.
Coaxial cable is commonly associated with cable TV installation, but is also used for specialized computers and other equipment.

There are two types of units: general purpose and special purpose. Electrical engineering and service technicians use the general purpose unit to test and maintain electronic equipment. They are also used for complex experiments and tests. A special purpose unit can be used to display the wave shape of a heartbeat, adjust the settings on an automotive ignition system or to provide insight into the wave shape of an electricity generator.

All oscilloscopes have the same basic features, including a display screen, various input connectors, control knobs, and buttons. There are battery-operated, portable units that can be carried in a backpack. Specialty scopes are usually attached to a rack or wheeled cart for easy transportation between locations.

Each unit has a grid etched into the face of the screen. The purpose of the grid is to eliminate parallax errors, or differences in the orientation of an object based on different lines of sight. For example, if the oscilloscope screen is viewed from a standing position, looking down on the output, the results will differ than if the screen is viewed straight on.

The input connectors are usually coaxial connectors, binding posts or banana plugs. If the signal source or electrical device has a coaxial connector, then the two units are connected with a basic coaxial cable. If not, then the scope probe is used.

This specialized cable is provided with oscilloscopes and has a standard input resistance of 1 mega ohm. A high frequency unit provides the capacity for a 50 ohm input. Special purpose units require additional training before they can be used in laboratory work, due to the complexity of the machine.

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Discussion Comments


@everetra - At our local community college they teach courses on electrical engineering. Of course you need to have an oscilloscope for some of the lessons.

Oscilloscopes can be expensive, especially the real high tech kind that have a bunch of bells and whistles. However, some of the engineering companies in town have stepped up to this demand, by donating their used oscilloscopes to the college.

It’s a reciprocal arrangement actually. The companies are hoping to get qualified interns in return – so it’s a win-win situation. The college benefits because they get high quality, industry tested equipment at no cost.


I work for a software company that services the electrical utilities industry. We have digital oscilloscopes everywhere in our lab. Actually most of these devices are hooked up to other units, called relay test equipment.

The units are hooked up to the computer using a USB or R232 serial connection. I’ve seen them operate but I don’t really understand what the patterns mean, only that they are sine waves of some sort or another.

Our basic use for these systems is to monitor how well our relay equipment can ramp up to a certain current, with the oscilloscope waves reflecting the frequencies.

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