OSC-2 · FG-2

Measurement tips

Practical procedures for the OSC-2 and FG-2. Tips marked Live audio need the sound card, so they work only when the page runs on its own site (for example on Vercel), not in the preview inside Claude. Control names are those printed on the panel; see the manual for details.

With the generator

A stable picture in four steps

  1. Start in AUTO: a trace is always visible, even without a trigger.
  2. Set SOURCE to the channel that carries the signal you want to keep still.
  3. Turn LEVEL until it lies inside the signal — the TRIG'D lamp lights and the picture stops.
  4. Choose SLOPE to start on the rising or falling edge. For a clean, repetitive signal switch to NORM: the screen then shows only properly triggered sweeps.
With the generator

Measuring voltage

Count the vertical divisions and multiply by the deflection coefficient:

Vpp = (divisions) × VOLTS/DIV
  1. Set COUPLING to GND and move the trace with POSITION ↕ onto a graticule line — this is your 0 V reference.
  2. Switch back to DC and choose VOLTS/DIV so that the signal is four to six divisions high: the reading is then most accurate.
  3. Example (preset Default): the CH1 sine spans 4 divisions at 1 V/div, so Vpp = 4 V. For a sine the RMS value is Vpp / (2√2) = 1.41 V — compare with the readings card.
  4. DC level: set the generator OFFSET to +1.5 V. In DC the trace rises 1.5 divisions above the reference; in AC it returns to the reference, because AC coupling removes the DC component.
With the generator

Measuring period and frequency

T = (divisions) × TIME/DIV    f = 1 / T
  1. Measure between corresponding points of the waveform, preferably zero crossings on the horizontal centre line, where the trace is steep.
  2. Measure over several periods and divide: the error of reading is shared among them. Example (preset Default, CH2): at 0.2 ms/div four periods of the 2 kHz square wave span 10 divisions, so T = 10 × 0.2 ms / 4 = 0.5 ms and f = 2 kHz.
  3. For a fine reading of a single edge, switch on ×10: the effective time coefficient is TIME/DIV ÷ 10.
With the generator

Rise time with the 10 % and 90 % lines

Rise time is the time the signal needs to rise from 10 % to 90 % of its full amplitude. The dashed graticule lines are made for this: the signal must span exactly the 5 divisions between the 0 % and 100 lines.

  1. Use a signal with a known slope: GEN 1 WAVEFORM triangle, 1 kHz, AMPLITUDE 5 Vpp, OFFSET 0; CH1 at 1 V/div, POSITION ↕ 0. The triangle now runs exactly from the 0 % to the 100 % line.
  2. Set A TIME/DIV to 0.1 ms and trigger on the rising slope.
  3. Read the horizontal distance between the crossings of the 10 and 90 lines: 4 divisions = 0.4 ms. Check: the ramp rises 5 V in 0.5 ms, and 80 % of that takes 0.4 ms.
  4. The OSC-2 has no amplitude fine control; set the 5 divisions with the generator AMPLITUDE. On a real instrument the measured value also contains the rise time of the oscilloscope itself: tsignal = √(tmeasured² − tscope²). Here tscope = 0.
With the generator

Phase difference — dual-trace method

φ = 360° × Δt / T
  1. Both outputs sine, 1 kHz, 4 Vpp; GEN 2 PHASE 45°. MODE DUAL, both channels 1 V/div, both traces centred (set the zero lines with GND).
  2. A TIME/DIV 0.1 ms: one period T = 1 ms = 10 divisions.
  3. Measure Δt between the rising zero crossings of the two traces: 1.25 divisions = 0.125 ms, so φ = 360° × 0.125 / 1 = 45°. CH2 crosses first: it leads.
  4. For small phase angles use ×10 to read Δt more precisely.
With the generator

Phase difference — Lissajous ellipse

sin φ = a / b
  1. Same setup as above (equal frequencies), MODE X-Y, both channels 1 V/div, both centred; GEN 2 PHASE 30°.
  2. Measure a, the distance between the two points where the ellipse crosses the vertical centre line, and b, its total height.
  3. Here a = 2 divisions and b = 4 divisions: sin φ = 0.5, φ = 30°. A straight line means 0° or 180°; with equal amplitudes a circle means 90°.
  4. The ellipse does not show the sign of the phase difference; use the dual-trace method to see which signal leads.
With the generator

Frequency ratio with Lissajous figures

fx : fy = (touch points on a vertical side) : (touch points on the top)
  1. Preset Lissajous 3:2: CH1 (X) 300 Hz, CH2 (Y) 200 Hz.
  2. Count where the figure touches the right side (3) and the top (2): fx : fy = 3 : 2. The XY ratio card confirms it.
  3. If the figure is an open curve that retraces itself, the count is wrong — change one PHASE slightly until the figure closes.
  4. If the figure slowly turns, the ratio is not exactly whole: the frequencies drift against each other.
With the generator

Beats

  1. Preset Beats: 1000 Hz and 1100 Hz, equal amplitude, MODE ADD, 5 ms/div.
  2. The envelope of the sum repeats with the difference frequency: fbeat = |f1 − f2| = 100 Hz, i.e. every 10 ms = 2 divisions.
  3. Turn one generator's FREQUENCY closer to the other: the beats slow down. With both AUDIO switches on you can also hear them.
With the generator

Precise time intervals with the delayed sweep

Δt = (DELAY₂ − DELAY₁) × A TIME/DIV
  1. Preset Delayed sweep: a 1 kHz pulse, A 0.5 ms/div, B 10 µs/div, DISPLAY A INT. The bright section shows what B will display.
  2. Move the bright section onto a rising edge with DELAY, then switch DISPLAY to B. Place the edge on a chosen graticule line and note DELAY₁ (here 3.98).
  3. Turn DELAY back to the previous edge and put it on the same line: DELAY₂ = 1.98. Δt = 2.00 × 0.5 ms = 1.000 ms, so f = 1.000 kHz.
  4. Use Shift with the mouse wheel for 0.02-division steps. Because B is 50 times faster than A, the edge position is read much more precisely than on the A sweep.
With the generator

Time markers with the Z input

  1. Preset Z modulation: GEN 2 gives a 10 kHz square wave from 0 V to +5 V (5 Vpp, OFFSET +2.5 V) into the Z INPUT.
  2. Every +5 V half-period blanks the beam: the trace becomes a dashed line with one dash and gap every 0.1 ms — at 0.2 ms/div, two per division.
  3. Use them as a time scale, or set GEN 2 to 1 kHz for 1 ms markers. A negative Z voltage brightens instead of blanking.
With the generator · Live audio

External trigger for noisy signals

  1. Preset Noisy signal: the displayed sum is a sine with noise.
  2. Set SOURCE to EXT and EXT TRIG IN to GEN 1 (the clean sine): the picture stays still. With GEN 2 (the noise) as trigger it falls apart.
  3. With live audio: GEN 1 plays a tone (AUDIO (LEFT) on), CH1 INPUT AUDIO IN picks it up with the microphone, trigger EXT from GEN 1. However weak the microphone signal, the picture is synchronous with the generator.
Live audio

Capturing a single event (clap, click)

  1. CH1 INPUT AUDIO IN, VOLTS/DIV 50 mV, A TIME/DIV 5 ms.
  2. Trigger SOURCE CH1, LEVEL a little above the background noise, MODE SINGLE.
  3. Press SINGLE RESET (READY lights) and clap. One sweep is recorded and stays on the screen.
  4. Move the trace right with POSITION ↔ to see the moments just before the trigger as well.
Live audio

Measuring the speed of sound

  1. GEN 1: pulse, 5 Hz, moderate VOLUME, AUDIO (LEFT) on — each rising edge makes a click in the loudspeaker.
  2. CH1 AUDIO IN (microphone); trigger EXT from GEN 1, SLOPE + ↑, NORM; A TIME/DIV 10 ms. The click appears some tens of milliseconds after the trigger: the computer adds a constant audio latency.
  3. Switch DISPLAY to A INT, move the bright section onto the click with DELAY, then switch to B with B TIME/DIV 1 ms.
  4. Note where the click starts, then move the microphone 34 cm further from the loudspeaker: the click moves about 1 ms (1 division) to the right — sound travels about 343 m/s at 20 °C. Only this change is meaningful, not the absolute delay.
Live audio

Stereo picture of music (X-Y)

  1. CH1 and CH2 INPUT AUDIO OUT (left channel → X, right → Y), MODE X-Y, 0.1–0.2 V/div, A TIME/DIV 5–10 ms, high PERSISTENCE.
  2. A mono signal draws a line rising at 45°; a wide stereo image a cloud; a phase-reversed channel the other diagonal.
  3. Studio phase meters (goniometers) rotate this picture by 45° so that mono is vertical.
Live audio

Examining your sound card

  1. Connect the headphone output to the line input with a cable (or hold the microphone close to the loudspeaker). GEN 1 square wave to AUDIO (LEFT), CH1 AUDIO IN.
  2. At 50 Hz the flat tops of the square wave sag: the sound card is AC-coupled, like the AC coupling of a real oscilloscope at low frequencies.
  3. At 5 kHz the edges are rounded. Measure the 10–90 % rise time with ×10 and estimate the bandwidth: B ≈ 0.35 / tr.
General

Typical mistakes

  • COUPLING left on GND — a flat line.
  • Trigger SOURCE on a channel without signal, or LEVEL outside the signal: TRIG'D stays dark; in AUTO the picture runs, in NORM it disappears.
  • SINGLE mode waiting for a trigger (READY lit) — the screen stays empty until the event comes.
  • In ADD the sum uses the CH1 VOLTS/DIV; in X-Y too short an A TIME/DIV draws only part of the figure.
  • ×10 or DISPLAY B forgotten on: the time scale is not what you think.

Literature