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What does an oscilloscope measure?

Most consumer products include electronic circuits or components, and an oscilloscope is used throughout the product design process to test those components. But what is an oscilloscope? And what does an oscilloscope measure?

An oscilloscope is an instrument that graphically displays electrical signals and shows how those signals change over time. Engineers use oscilloscopes to measure electrical phenomena and quickly test, verify, and debug their circuit designs. The primary function of an oscilloscope is to measure voltage waves. Those waves are displayed on a graph that can tell you many things about a signal, such as:

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

At a very basic level, the graph displayed on an oscilloscope shows how the signal changes over time with voltage displayed vertically on the Y axis and time represented horizontally on the X axis.

 

Oscilloscope display showing a graph of how a signal changes over time

 

The intensity or brightness of the signal on the scope’s display is sometimes called the Z-axis. On Digital Phosphor Oscilloscopes (DPO), the Z-axis can be represented by color grading of the display.

 

Z-axis on an oscilloscope showing the intensity and brightness of a signal

 

For more information about reconstructing signals, signal integrity, and waveform measurements, read about the oscilloscopes basics.

What does an oscilloscope measure?

While oscilloscopes are primarily designed to measure volts, they can detect and measure a variety of other signals, including:

Current

current electrical diagramThere are a few ways to use an oscilloscope to measure current; one would be to measure the voltage dropped across a shunt resistor. The other is to simply use a current probe.

Sound

sound electrical diagramIt is possible to measure sound through an oscilloscope. You would need a transducer (to ‘convert’ the audio signal to a voltage), which you then connect to a channel on the scope. You’ll then display the signal as a corresponding voltage vs. time.

Capacitance

capacitance electrical diagramWhile an oscilloscope won’t give a direct measure of capacitance, it can be used to measure a time constant in order to find the actual capacitance of an electrical system or component with an Arbitrary Function Generator.

DC Voltage

DC Voltage electrical diagramMost modern oscilloscopes provide the option to measure DC voltage automatically. However you can measure it manually by ‘counting’ the vertical reticules and multiplying by the volts per division.

Frequency

frequency electrical diagramMuch like with DC voltage, most modern oscilloscopes measure frequency automatically. However, it is possible to calculate the frequency manually by calculating the period of the signal (using cursors or the horizontal reticules) and dividing 1 by the period giving you the frequency.

Inductance

inductance electrical diagramIf you don’t have an LCR meter, you can measure inductance with an oscilloscope and a function generator. This will be a simple measurement with a 3 to 5% uncertainty value.

Find the right oscilloscope for your application

Not all oscilloscopes are created equal. So, before deciding which machine to invest in, it’s important to understand your project requirements and the type of oscilloscope you might need to get the most efficient, accurate measurements.

There are a number of things to consider when deciding which oscilloscope to buy, including bandwidth, rise time, sample rate, channel density and compatible probes. Read our breakdown of how to choose an oscilloscope or explore our full line of oscilloscopes to find the right one for your application.