Measure Electronic Waves: How to Calibrate an Oscilloscope

An oscilloscope is an incredibly useful tool to have on your electronics workbench. Unfortunately, oscilloscopes are also expensive, costing at least a few hundred dollars. So most electronic hobbyists get by without one. But if you have one, you must first verify the settings of some key controls on your oscilloscope before you take a measurement.

The exact steps you need to follow to set up your oscilloscope vary depending on the exact type and model of your scope, so be sure to read the instruction manual that came with your scope. But the general steps should be as follows:

  1. Examine all the controls on your scope and set them to normal positions.

    For most scopes, all rotating dials should be centered, all pushbuttons should be out, and all slide switches and paddle switches should be up.

  2. Turn your oscilloscope on.

    It it's the old-fashioned CRT kind, give it a minute or two to warm up.

  3. Set the VOLTS/DIV control to 1.

    This sets the scope to display one volt per vertical division. Depending on the signal you're displaying, you may need to increase or decrease this setting, but one volt is a good starting point.

  4. Set the TIME/DIV control to 1 ms.

    This control determines the time interval represented by each horizontal division on the display. Try turning this dial to its slowest setting. Then, turn the dial one notch at a time and watch the dot speed up until it becomes a solid line.

  5. Set the Trigger switch to Auto.

    The Auto position enables the oscilloscope to stabilize the trace on a common trigger point in the waveform. If the trigger mode isn't set to Auto, the waveform may drift across the screen, making it difficult to watch.

  6. Connect a probe to the input connector.

    If your scope has more than one input connector, connect the probe to the one labeled A.

    Oscilloscope probes include a probe point, which you connect to the input signal and a separate ground lead. The ground lead usually has an alligator clip. When testing a circuit, this clip can be connected to any common ground point within the circuit. In some probes, the ground lead is detachable, so you can remove it when it isn't needed.

  7. Touch the end of the probe to the scope's calibration terminal.

    This terminal provides a sample square wave that you can use to calibrate the scope's display. Some scopes have two calibration terminals, labeled 0.2 V and 2 V. If your scope has two terminals, touch the probe to the 2 V terminal.

    For calibrating, it's best to use an alligator clip test probe. If your test probe has a pointy tip instead of an alligator clip, you can usually push the tip through the little hole in the end of the calibration terminal to hold the probe in place.

    It isn't necessary to connect the ground lead of your test probe for calibration.

  8. If necessary, adjust the TIME/DIV and VOLTS/DIV controls until the square wave fits nicely within the display.

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  9. If necessary, adjust the Y-POS control to center the trace vertically.

  10. If necessary, adjust the X-POS control to center the trace horizontally.

  11. If necessary, adjust the Intensity and Focus settings to get a clear trace.

  12. Congratulate yourself!

    You're now ready to begin viewing the waveforms of actual electronic signals.

Remember that the controls of every oscilloscope make and model are unique. Be sure to read the owner's manual that came with your oscilloscope to see if there are any other setup or calibration procedures you need to follow before feeding real signals into your scope.

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