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Using an oscilloscope

Measurement and instruments · Beginner · about 10 minutes · part of Zen’s Electronics Design Mastery

A multimeter gives you one number. An oscilloscope draws the voltage against time, so you see the shape of a signal. The screen is a grid: each vertical division is worth the VOLTS/DIV setting, each horizontal division is worth the TIME/DIV setting. Count divisions and multiply. The trigger holds the picture still by starting every sweep at the same point of the wave.

Using an oscilloscope: the circuit on the simulator's bench

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How it works

Vertical (volts): CH1 is set to 1 V/div. A 3.99 V peak-to-peak wave is 3.99 V ÷ 1 V = 4.0 divisions tall.

Horizontal (time): TIME/DIV is 200 µs. One period T = 1 ÷ f = 1 ÷ 1 kHz = 1 ms, so one cycle is 5.0 divisions wide and the 10-division screen shows 2.0 cycles.

Read it backwards, the way you will on a real scope: count the divisions, multiply by the setting. Height × V/div = Vpp; cycle width × time/div = T; f = 1 ÷ T.

From Vpp: Vpeak = Vpp ÷ 2 = 1.995 V; RMS (what a multimeter shows) = Vpeak ÷ √2 for a sine = 1.411 V.

Channel 2 (blue) is across R2, the bottom of a 10 kΩ / 10 kΩ divider: the same wave at half the height. The black ground clip goes to the circuit’s common: both channels measure against it.

Try it on the bench

  1. Select the scope and turn CH1 VOLTS/DIV to 0.5 V: the wave grows to twice the height, but the voltage has not changed. Only the scale has.
  2. Turn TIME/DIV to 1 ms: ten times as many cycles squeeze onto the screen. Turn it to 50 µs: you see a quarter of one cycle.
  3. Select the function generator and set it to 2 kHz: the cycles get half as wide. Count them to check the frequency yourself.
  4. Change the wave to square, then triangle. The peak-to-peak stays the same but the RMS changes (see the theory).
  5. Set the generator’s DC offset to 1 V: the whole wave lifts by one division and the CH1 average reads 1 V.
  6. Move the trigger level above the top of the wave: in AUTO the picture starts to drift, because nothing crosses the level any more. Bring it back and it locks again.
  7. Open Tools → Scope window for cursors and an FFT of the same signals.

Parts on the bench

In the course

Zen’s Electronics Design Mastery, module “AC & Reactance”.

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