HOW-TO GUIDE
What Is an Oscilloscope?
By the OhmSavvy Research Team ·
What an oscilloscope shows you
The screen is a grid called the graticule. On most scopes it is 10 divisions wide and 8 divisions tall. The vertical axis is voltage and the horizontal axis is time, and you set how much each division is worth with two controls: volts per division (V/div) and time per division (s/div, ms/div, µs/div and so on). The bright line drawn across the grid is called the trace.
Because the picture has both a voltage scale and a time scale, you can read a lot from one trace: how big the signal is, how often it repeats, how quickly it rises and falls, and whether it carries noise or spikes. Our guide on how to read an oscilloscope screen walks through doing this by counting divisions.
The controls on the front panel
A digital scope's front panel looks busy, but the controls fall into a few groups. The vertical knob sets V/div for each channel, the horizontal knob sets time/div, and the trigger level knob decides which point on the signal each capture lines up on. Buttons such as Auto, Run/Stop and Single set up the display or freeze a capture, and the probe compensation terminals give you a safe square wave to practice on.
Two-channel and handheld scopes have fewer inputs and often share one knob between functions, but the ideas are the same. Our guide on how to use an oscilloscope takes you through each control in a first session.
What a scope can reveal that a meter cannot
A multimeter averages or summarizes a signal into one number. That is ideal for steady values, but it hides anything that changes quickly. A scope shows the changes themselves:
Amplitude
Peak, peak-to-peak and DC level of a signal, read from the vertical scale.
Frequency and period
How often a signal repeats, from the horizontal scale (f = 1/T).
Wave shape
Whether a square wave is clean, rounded, or ringing on its edges.
Noise and ripple
Small fluctuations riding on a supply rail that a meter averages away.
Glitches
Brief dropouts or spikes, captured with a trigger or single-shot mode.
Timing
With two or more channels, how one signal lines up against another.
For a side-by-side look at which tool fits which job, see when to use an oscilloscope vs a multimeter.
How a digital oscilloscope works, briefly
Almost every scope sold new today is digital. The probe carries the signal to an input amplifier, which scales it to suit the V/div setting. An analog-to-digital converter then samples the voltage at a fixed rate, measured in samples per second (for example 1 GSa/s, one billion samples a second), and stores the samples in acquisition memory. The scope draws those stored points on the screen. A trigger tells the scope where to start each capture, for example every time the signal rises through 1 V, so a repeating waveform sits still on screen instead of rolling across it. Our guide on how to trigger an oscilloscope covers this in detail.
01
Probe
Picks up the signal at the circuit
02
Attenuator / amp
Scales it to suit the V/div setting
03
ADC (sampling)
Measures the voltage, e.g. 1 GSa/s
04
Memory
Stores the samples of one capture
05
Display
Draws the stored points as the trace
Each stage sets a limit. The front end's bandwidth caps how fast a signal it can pass without shrinking it, the sample rate caps how finely the ADC can record it, and memory depth caps how long a stretch can be recorded at that rate. Those three limits are the specs covered further down.
The main types of oscilloscope
"Oscilloscope" covers several quite different instruments. These are the categories you will run into when shopping or reading forums:
| Type | What it is | Typical use |
|---|---|---|
| Analog (CRT) | The original design: the signal steers an electron beam across a phosphor screen in real time. No sample memory. | Mostly found second-hand or in older labs today |
| Digital storage (DSO) | Samples the signal, stores it in memory and draws it on an LCD. Can freeze, measure and save captures. | The standard bench scope for hobbyists, students and repair work |
| Mixed-signal (MSO) | A DSO with extra digital logic channels alongside the analog ones. | Debugging microcontroller buses and digital logic alongside analog signals |
| Handheld | Battery-powered, portable scopes, from pocket units to rugged field instruments. | Quick checks away from the bench, low-frequency signals, field service |
| PC / USB | A capture box that uses a computer for the display and controls. | Saving bench space; capability varies widely between models |
Within digital bench scopes the range is wide. The Siglent SDS1104X-E is a 4-channel, 100MHz model; the Hantek DSO2D10 is a 2-channel, 100MHz scope with a built-in waveform generator. At the other extreme, the pocket-sized FNIRSI DSO152 has a single channel and 200kHz of bandwidth: enough for audio-range and slow signals, but not for fast digital work.
Examples of each type
Handheld: pocket-sized, 1 channel, 200kHz bandwidth, 2.5 MSa/s.
Bench DSO: 4 channels, 50MHz, 1 GSa/s, 7-inch display.
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The specs that matter
Four numbers do most of the work when comparing scopes:
- Bandwidth (MHz): the frequency at which a sine wave is shown at about 70.7% of its true amplitude (the -3 dB point). A common rule of thumb is to choose 3 to 5 times the highest frequency you need to see. More on bandwidth.
- Sample rate (MSa/s or GSa/s): how many times per second the scope measures the voltage. On many scopes the headline figure is shared between active channels, so check your model's datasheet. What GSa/s means.
- Channels: how many signals you can view at once. Two is enough to compare an input and an output; four helps with digital timing and multi-rail power supplies.
- Memory depth: how many samples a single capture can hold. Deeper memory lets the scope keep a high sample rate over a longer time window.
Bandwidth is where scopes differ most. The four models mentioned on this page cover a 500-to-1 range: the FNIRSI DSO152's 200kHz is 250 times lower than the Rigol DS1054Z's 50MHz, and 500 times lower than the 100MHz of the Siglent SDS1104X-E and Hantek DSO2D10.
Bars use a logarithmic scale: each step is ten times the last.
Rule of thumb
What oscilloscopes are used for
Scopes show up anywhere the timing or shape of a signal matters, not just its average value. Common jobs include:
- Checking a microcontroller's PWM output, clock or serial data (UART, I2C, SPI) during a project.
- Looking for ripple and noise on a power supply rail that a meter reads as a steady value.
- Following an audio signal through an amplifier to see where it distorts or clips.
- Repair work: confirming whether a stage of a circuit is producing the signal it should.
- Learning electronics: seeing capacitors charge, filters roll off and oscillators start.
One safety point to know before you buy
Do you need one?
If you mostly check batteries, continuity and outlet voltages, a multimeter covers it, and our multimeter guide is the better starting point. If you build or repair circuits with anything that switches, oscillates or communicates, such as Arduino projects, audio gear or switching power supplies, a scope turns guesswork into something you can see. Most people who own a scope also keep a multimeter on the bench; the two tools answer different questions. When you are ready to choose one, start with our beginner oscilloscope picks, then learn how to compensate the probe before your first measurement.
Frequently asked questions
Can an oscilloscope measure current?
Not directly: a scope input measures voltage. To see current, the usual method is to measure the voltage across a small resistor of known value placed in the current path and divide by its resistance (I = V / R), or to use a current probe made for oscilloscopes. On a mains-powered scope, remember the probe ground clip is earthed, so place the resistor where the ground clip can safely connect.
Does an oscilloscope measure AC or DC?
Both. With DC coupling, the scope shows the whole signal, including any steady DC level, so a 5 V rail sits 5 V above the ground marker. With AC coupling, the DC part is blocked and only the changing part is shown, which is handy for magnifying a small ripple riding on top of a supply rail.
How much bandwidth does a beginner oscilloscope need?
Work out the fastest signal you expect to look at and apply the rule of thumb of 3 to 5 times that frequency. Audio-range and slow sensor signals can be viewed on a pocket scope with a few hundred kilohertz of bandwidth, while microcontroller clocks, PWM edges and serial buses benefit from a 50 to 100MHz bench scope.
Can an oscilloscope replace a multimeter?
Not in practice. A scope can read voltages, but it is not built for resistance, continuity or current checks, and it is bulkier for quick jobs. A multimeter gives one accurate number for steady values; a scope shows how a voltage changes over time. Most people who work on circuits keep both on the bench.
Is an oscilloscope hard to learn for a beginner?
The basics are quicker to learn than the number of buttons suggests. Most of the work comes down to four things: volts per division, time per division, the trigger and the measurement menu. Practicing on the scope's built-in probe compensation output, a safe low-voltage square wave, is the easiest way to learn what each control does.
