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How to Measure Wide Voltage Swings

For measuring electrical signals, whether relatively weak ones measuring in the millivolt range or those with wide voltage swings of several hundred volts, an oscilloscope is usually a technician's first choice. The oscilloscope displays signals as a real-time image on a graphical screen, and handles frequencies ranging from direct current, or DC, to several hundred megahertz. For moderately strong signals, it helps to have an attenuator probe for the oscilloscope. A 10x attenuator probe reduces the signal to one-tenth of its strength before sending it to the oscilloscope's input.

Things You'll Need

Oscilloscope probe with 10x attenuator switch
Oscilloscope

Instructions

- 1
  Turn off all power to your circuit or device under test.
- 2
  Slide the attenuator setting switch on the oscilloscope probe to the "10x" position.
- 3
  Attach the probe's BNC connector to the BNC male connector on the oscilloscope's channel one input.
- 4
  Clip the oscilloscope probe tip to the positive terminal of the circuit or device you are testing. Attach the probe's ground clip to the circuit's ground or negative terminal.
- 5
  Turn the oscilloscope on. Adjust its channel one input sensitivity to the largest setting for volts per division. This varies by oscilloscope, but it may be 10 volts per division. Set the channel one input coupling selector switch to alternating current, or AC.
- 6
  Turn the power on to the circuit or device under test. Read the voltage on the oscilloscope screen by counting the horizontal division lines between the signal's maximum and minimum peaks. Multiply the divisions by the volts per division setting, then multiply the result by 10 to obtain the actual reading. For example, if you set the oscilloscope to 10 volts per division, and you count three and one-half divisions, that is 35. Multiply by 10, the probe's attenuation factor, to get 350 volts.

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