Introduction: Why Waveform Reading Matters
Oscilloscope multimeters are powerful tools because they let you see electrical signals instead of just measuring them. ? Understanding waveforms helps diagnose faults that a normal digital multimeter cannot detect—such as noise, ripple, distortion, broken sensors, and unstable power supplies.
This guide explains how to read waveforms step-by-step using any modern oscilloscope multimeter.
The Basics: What Is a Waveform?
A waveform is a visual representation of how voltage changes over time. Every electrical system—AC mains, motors, sensors, electronics—creates a unique waveform.
You will commonly see:
- ? Sine wave — AC mains power
- ▫️ Square wave — PWM control, digital signals
- ? Triangle wave — some sensors, audio circuits
- ? Distorted wave — faulty power supply or noisy signal
Key Waveform Terms You Must Know
1️⃣ Amplitude (Voltage Level)
This is the height of the waveform—how high or low the voltage goes. Bigger amplitude = stronger signal.
2️⃣ Frequency (Hz)
How many times the pattern repeats per second.
- 50Hz → UK mains electricity
- 1kHz–20kHz → automotive sensors
- Up to MHz → electronics circuits
3️⃣ Duty Cycle (%)
Used for PWM signals—percentage of ON vs OFF time.
4️⃣ Noise / Ripple
The small unwanted spikes or wiggles on the waveform. Noise often indicates faulty wiring, interference, or bad grounding.
5️⃣ Rise & Fall Time
How fast the signal transitions from low to high.
Step-By-Step: How to Measure a Waveform
✔ Step 1 — Select Oscilloscope Mode
Turn the dial or press the “SCOPE” button on your oscilloscope multimeter.
✔ Step 2 — Connect Probes
Use the oscilloscope probes or normal test leads:
- Black → COM
- Red → V / Scope Input
✔ Step 3 — Set Voltage Range
Start with a higher range to avoid overloading.
✔ Step 4 — Set Time Base
This controls how much of the signal you see on the screen.
- Slow time base → good for 50Hz AC
- Fast time base → good for sensors, PWM, digital signals
✔ Step 5 — Stabilise the Waveform (Trigger)
Adjust trigger to lock the waveform so it doesn't move on the screen.
✔ Step 6 — Read the Signal
Check:
- Shape (sine, square, triangle)
- Amplitude (voltage)
- Frequency (Hz)
- Duty cycle (%)
- Noise / ripple
Examples of Common Waveforms
? 1. AC Mains (Sine Wave)
Should be a smooth, stable sine wave at 50Hz (UK). Ripple or distortion means power supply issues.
? 2. PWM Fan Control (Square Wave)
Higher duty cycle (%) = faster fan speed. Oscilloscope multimeter helps diagnose fan control faults.
? 3. Automotive Sensor Signal
Crank & camshaft sensors produce clean waveforms. Missing spikes or irregular shapes = sensor failure.
? 4. Power Supply Ripple Test
DC supplies should look flat. Ripple indicates bad capacitors or failing PSU.
Diagnosing Problems Using Waveform Shapes
✔ Distorted Sine Wave
May indicate inverter fault or harmonic distortion.
✔ Noisy Waveform
Caused by grounding issues, loose connections, interference.
✔ Flat Line (No Signal)
No power, broken wire, or dead sensor.
✔ Irregular PWM
Faulty motor controller or corrupted signal.
Safety Tips for Using Oscilloscope Multimeters
- Use CAT-rated meters for mains testing (CAT III or CAT IV)
- Never touch metal probe tips during measurement
- Start with highest voltage range
- Use insulated probes for high-energy systems
Why Oscilloscope Multimeters Are Better than Normal DMMs
- See waveform shape instead of only numbers
- Diagnose faults instantly
- Portable — ideal for field engineers
- Great for automotive, HVAC, EV, and power systems
- Affordable compared to full bench oscilloscopes
Final Thoughts
Learning to read waveforms unlocks the full power of your oscilloscope multimeter. With waveform analysis, you can diagnose problems that no normal multimeter can detect.
This guide covered everything from waveform basics to real-world signals. In the next blog, we will explore 10 practical uses of an oscilloscope multimeter for electricians, automotive engineers, HVAC, EV technicians and electronics repair. ?