Skip to content

Laboratory Measurement Techniques

Summary

This chapter covers the essential laboratory skills and equipment used throughout the course. Students will learn to operate oscilloscopes, function generators, multimeters, and spectrum analyzers to measure and characterize circuit behavior. The chapter addresses practical skills including proper probe techniques, triggering methods, and circuit prototyping on breadboards. Understanding measurement errors, loading effects, and calibration ensures accurate and reliable experimental results. Safety practices for working with electrical circuits are also emphasized.

Concepts Covered

This chapter covers the following 25 concepts from the learning graph:

  1. Multimeter
  2. Oscilloscope
  3. Function Generator
  4. DC Power Supply
  5. Spectrum Analyzer
  6. Voltage Measurement
  7. Current Measurement
  8. Resistance Measurement
  9. Frequency Measurement
  10. Phase Measurement
  11. Oscilloscope Probe
  12. Probe Compensation
  13. Triggering
  14. Time Base
  15. Vertical Sensitivity
  16. AC Coupling
  17. DC Coupling
  18. Breadboard
  19. Prototyping
  20. Soldering
  21. Circuit Debugging
  22. Measurement Error
  23. Loading Error
  24. Calibration
  25. Safety Practices

Prerequisites

This chapter builds on concepts from:

title: Laboratory Measurement Techniques description: Master the essential equipment and skills for measuring, building, and debugging circuits generated_by: chapter-content-generator v0.03 date: 2026-01-30

Introduction: Where Theory Meets Reality

You can analyze circuits on paper all day, but circuits only become real when electrons start flowing through actual components. The laboratory is where you discover whether your calculations match reality—and when they don't, you learn the most.

This chapter covers the practical skills that separate paper engineers from real ones: how to use the essential instruments (oscilloscopes, multimeters, function generators), how to build reliable prototype circuits, and how to debug when things inevitably go wrong. We'll also discuss measurement accuracy, loading effects, and the safety practices that keep you and your equipment intact.

These skills aren't glamorous, but they're invaluable. The engineer who can quickly diagnose a misbehaving circuit is worth far more than one who can only calculate theoretical behavior. Master your instruments, and you'll have confidence to tackle any circuit challenge.

The Essential Lab Instruments

Multimeter

The multimeter (or DMM—Digital MultiMeter) is the most basic and frequently used instrument. It measures:

Voltage (DC and AC):

  • High input impedance (10 MΩ typical)
  • Measure in parallel with the component
  • DC readings: set to DC mode
  • AC readings: True RMS for accurate non-sinusoidal measurements

Current (DC and AC):

  • Measure in series with the circuit (break the circuit)
  • Low input impedance (burden voltage affects circuit)
  • Use appropriate range to avoid blowing the fuse!

Resistance:

  • Apply test current and measure voltage drop
  • Disconnect component from circuit (or power off)
  • Cannot measure accurately while circuit is powered
Measurement Connection Multimeter Mode Considerations
Voltage Parallel V (DC or AC) High Z input
Current Series A (DC or AC) Break circuit
Resistance Across component Ω Power OFF
Continuity Across path Beep mode Quick test

Oscilloscope

The oscilloscope displays voltage as a function of time—the single most important instrument for understanding circuit behavior.

Key capabilities:

  • Visualize waveform shape
  • Measure frequency, period, rise time
  • Observe multiple channels simultaneously
  • Capture transient events
  • Perform frequency analysis (FFT on digital scopes)

Controls you must understand:

  1. Time base - Horizontal scale (time/division)
  2. Vertical sensitivity - Volts/division
  3. Triggering - When to start drawing
  4. Coupling - AC/DC input selection
  5. Probe attenuation - 1X vs 10X

Diagram: Oscilloscope Interface Guide

Oscilloscope Interface Guide Type: microsim Bloom Level: Apply (L3) Bloom Verb: use Learning Objective: Students will use oscilloscope controls to properly display and measure a waveform. Visual elements: - Simulated oscilloscope display with graticule - Waveform that responds to control changes - Control panel mimicking real oscilloscope - Measurement readouts (frequency, Vpp, Vavg) - Trigger level indicator Interactive controls: - Slider: Time/div (1μs to 1s, decades) - Slider: Volts/div (10mV to 10V, 1-2-5 sequence) - Slider: Trigger level - Radio: Trigger source (CH1, CH2, External) - Radio: Trigger edge (Rising, Falling) - Toggle: AC/DC coupling - Slider: Vertical position Input signal controls: - Dropdown: Waveform (sine, square, triangle) - Slider: Frequency (10Hz to 100kHz) - Slider: Amplitude - Slider: DC offset Goals/exercises: - "Display exactly 2 cycles" - "Measure the peak-to-peak voltage" - "Find the frequency using cursors" Default parameters: - 1 kHz sine wave, 2 Vpp - Time/div: 500 μs - Volts/div: 1 V Canvas layout: - Scope display: 500 × 400 pixels - Controls panel: 200 × 400 pixels (side) - Control area: 100 pixels below Implementation: p5.js

Function Generator

The function generator produces standard waveforms for testing circuits:

Output waveforms:

  • Sine wave
  • Square wave
  • Triangle/ramp wave
  • Pulse (adjustable duty cycle)
  • Arbitrary (advanced generators)

Key settings:

Parameter Typical Range Purpose
Frequency 1 Hz - 10 MHz Set test frequency
Amplitude 0 - 10 Vpp Set signal level
DC offset ±5V Add DC bias
Output impedance 50Ω Affects loaded voltage

Important: Most generators have 50Ω output impedance. Into a high-impedance load, you get the displayed voltage. Into a 50Ω load (matched), you get half the displayed voltage.

DC Power Supply

The DC power supply provides controlled voltage and current for powering circuits.

Features to understand:

  • Voltage setting: Adjustable output voltage
  • Current limit: Maximum current (protects circuit and supply)
  • Constant voltage (CV) mode: Maintains set voltage regardless of load
  • Constant current (CC) mode: Limits current when load demands more than limit

Dual/triple supplies: Provide multiple independent or tracking outputs (useful for ±15V op-amp supplies).

Spectrum Analyzer

The spectrum analyzer displays amplitude vs. frequency—the frequency domain view of a signal.

Uses:

  • Identify harmonic content
  • Measure THD (Total Harmonic Distortion)
  • Find interference sources
  • Verify filter response

Key settings:

  • Center frequency: Middle of display
  • Span: Frequency range displayed
  • Resolution bandwidth (RBW): Frequency resolution
  • Reference level: Top of display (dBm or dBV)

Measurement Techniques

Voltage Measurement

DC voltage:

  1. Set multimeter to DC voltage range
  2. Connect probes in parallel with component
  3. Black to reference (ground), red to test point
  4. Read voltage (positive or negative)

AC voltage with oscilloscope:

  1. Connect probe ground to circuit ground
  2. Touch probe tip to test point
  3. Adjust volts/div for readable display
  4. Set time/div to show a few cycles
  5. Read Vpp or use automatic measurement

Current Measurement

Current measurement requires breaking the circuit:

  1. With multimeter:
  2. Set to current range (A or mA)
  3. Open the circuit where you want to measure
  4. Insert meter in series

  5. Current flows through the meter

  6. With oscilloscope (indirect):

  7. Measure voltage across a known resistor
  8. Calculate: I = V/R
  9. Or use a current probe

Current Measurement Caution

Never connect a current meter in parallel with a component! The meter's low resistance will create a short circuit, potentially damaging the meter, circuit, or both.

Resistance Measurement

  1. Power off the circuit completely
  2. Disconnect at least one lead of the component (to avoid parallel paths)
  3. Set meter to Ω range
  4. Touch probes to component leads
  5. Read resistance

Troubleshooting tip: If reading seems wrong, check for parallel paths in the circuit that could affect the measurement.

Frequency Measurement

With oscilloscope:

\[f = \frac{1}{T}\]

Measure period T from the display, or use automatic frequency measurement.

With frequency counter: Connect signal, read frequency directly (more accurate than scope).

Phase Measurement

With dual-channel oscilloscope:

  1. Connect reference signal to CH1
  2. Connect signal to measure to CH2
  3. Measure time delay Δt between corresponding points (zero crossings)
  4. Calculate phase:
\[\phi = \frac{\Delta t}{T} \times 360°\]

With Lissajous patterns: X-Y mode shows phase relationship as an ellipse shape.

Oscilloscope Probes

Probe Types

Passive 10X probe:

  • Most common type
  • Divides signal by 10 (scope compensates)
  • Higher input impedance (10 MΩ)
  • Lower capacitance loading
  • Wider bandwidth

1X probe (direct):

  • No attenuation
  • Lower input impedance
  • More capacitance loading
  • Limited bandwidth
  • Good for very small signals
Parameter 1X Probe 10X Probe
Input impedance 1 MΩ 10 MΩ
Capacitance ~100 pF ~10 pF
Bandwidth Limited Higher
Minimum signal ~1 mV ~10 mV

Probe Compensation

10X probes must be compensated to match the oscilloscope input. An uncompensated probe distorts square waves:

  • Under-compensated: Rounded corners
  • Over-compensated: Overshoot at corners
  • Correct: Flat tops and sharp corners

Compensation procedure:

  1. Connect probe to calibration output (square wave)
  2. Observe waveform
  3. Adjust trimmer screw on probe
  4. Repeat until square wave is flat

Triggering: Capturing the Right Moment

Triggering tells the oscilloscope when to start displaying a waveform. Without proper triggering, the display rolls or appears unstable.

Trigger parameters:

  • Source: Which signal to trigger on (CH1, CH2, External, Line)
  • Level: Voltage threshold for trigger
  • Edge: Rising or falling edge
  • Mode: Auto (always runs), Normal (waits for trigger)

Triggering tips:

  • For repetitive signals: Trigger on the signal itself
  • For non-repetitive events: Use Normal mode and wait
  • For signals synchronized to power line: Use Line trigger
  • For multiple signals: Trigger on the reference channel

Coupling: AC vs DC

DC coupling passes the complete signal including any DC offset.

AC coupling blocks the DC component, showing only the AC variation.

When to use each:

Use DC Coupling Use AC Coupling
Measuring DC levels Small AC on large DC
Viewing full waveform Ignoring DC bias
Accurate DC measurements Noise on power supply
Default for most work Examining ripple

Building Circuits: Breadboards and Prototyping

Breadboard

A breadboard allows rapid circuit construction without soldering.

Layout:

  • Terminal strips: Rows of 5 connected holes
  • Bus strips: Long connected rows for power/ground
  • Center gap: Spans between IC pins

Best practices:

  • Keep wires short and flat
  • Use consistent colors (red = +V, black = ground)
  • Place ICs across the center gap
  • Use multiple grounds (avoid ground bounce)
  • Don't exceed current limits (typically 1A per strip)

Limitations:

  • High capacitance between strips (~2 pF)
  • Limited to low frequencies (< 10 MHz practical)
  • Connection reliability varies
  • Not suitable for high-current or high-voltage

Soldering

Soldering creates permanent electrical connections.

Good solder joint characteristics:

  • Shiny appearance (not dull)
  • Flows smoothly onto both surfaces
  • Concave fillet shape
  • Component lead visible through solder

Common defects:

  • Cold joint: Dull, grainy appearance (insufficient heat)
  • Insufficient solder: Weak connection
  • Solder bridge: Unintended connection between pads
  • Overheated: Damaged component or lifted pad

Circuit Debugging

Debugging strategy:

  1. Verify power: Is supply voltage correct at IC pins?
  2. Check connections: Follow schematic, verify each wire
  3. Divide and conquer: Isolate sections, test independently
  4. Signal trace: Follow signal path, find where it fails
  5. Compare to theory: Does behavior match expectations?

Common problems:

Symptom Possible Cause
No output No power, broken connection
DC offset wrong Bias resistor error, loading
Gain incorrect Wrong resistor value
Oscillation Positive feedback, layout issue
Noise/hum Ground loop, pickup
Distortion Clipping, nonlinearity

Measurement Errors

Loading Error

Loading error occurs when the measurement instrument affects the circuit being measured.

Voltage measurement loading:

\[V_{measured} = V_{actual} \times \frac{R_{meter}}{R_{meter} + R_{source}}\]

With high-impedance meters (10 MΩ), loading is usually negligible unless the source impedance is also high.

Example: Measuring across a 1 MΩ resistor with a 10 MΩ meter: [V_{measured} = V_{actual} \times \frac{10M}{10M + 1M} = 0.91 V_{actual}]

That's a 9% error!

Other Error Sources

  • Calibration error: Instrument reads wrong
  • Resolution error: Limited digits/divisions
  • Temperature drift: Readings change with temperature
  • Noise: Random fluctuations in reading

Calibration

Calibration verifies and adjusts instrument accuracy against known standards.

Checks you can perform:

  • Zero offset: Does meter read 0 with leads shorted?
  • 1 kHz test: Does scope show correct frequency?
  • Probe compensation: Is square wave flat?

Professional calibration uses certified references and should be done periodically for critical measurements.

Safety Practices

Electrical safety rules:

  1. Power off before making connections
  2. One hand rule: Keep one hand in pocket when probing live circuits
  3. Current limits: Use power supply current limiting
  4. Fuse protection: Ensure fuses are appropriate rating
  5. Capacitor discharge: Large capacitors hold charge—discharge before handling
  6. No jewelry: Remove rings, watches when working
  7. Inspect equipment: Don't use damaged cables or probes

Voltage limits:

Voltage Risk Level Precautions
< 50V DC Generally safe Basic precautions
50-500V Can be lethal Extreme care
> 500V Dangerous Special training required
Line voltage (120/240V) Serious hazard Isolation, GFCI

Respect Electricity

Even low voltages can be dangerous under the right conditions (wet skin, direct heart path). Always assume circuits are live until verified otherwise, and never work alone on high-voltage equipment.

Self-Check Questions

1. Why should you use a 10X probe instead of 1X for most oscilloscope measurements?

The 10X probe has several advantages:

  1. Higher input impedance (10 MΩ vs 1 MΩ): Less loading on the circuit

  2. Lower input capacitance (~10 pF vs ~100 pF): Less distortion of fast edges

  3. Higher bandwidth: Typically 200-500 MHz vs 10-20 MHz

  4. Better noise immunity: Higher impedance reduces pickup

The only disadvantage is a 10× reduction in displayed signal, making very small signals harder to see. For signals above ~10 mV, the 10X probe is almost always the better choice.

2. Your oscilloscope shows a slowly drifting waveform instead of a stable display. What control should you adjust?

The trigger level needs adjustment.

The trigger level must cross the waveform consistently for stable display. If it's set too high or too low (outside the waveform range), the scope won't find valid trigger points and the display will drift.

Also check: - Trigger source is correct channel - Trigger mode is Auto or Normal - Trigger edge matches the waveform transition you want

3. When measuring the output voltage of a sensor with 100 kΩ source impedance, your 10 MΩ multimeter reads 4.95V. What is the actual sensor voltage?

The measured voltage is reduced by the voltage divider formed by source and meter impedance:

\[V_{measured} = V_{actual} \times \frac{R_{meter}}{R_{meter} + R_{source}}\]
\[4.95 = V_{actual} \times \frac{10M}{10M + 0.1M}\]
\[4.95 = V_{actual} \times 0.99\]
\[V_{actual} = \frac{4.95}{0.99} = 5.00 \text{ V}\]

The loading error is only 1% in this case because the meter impedance is 100× the source impedance.

4. Your breadboard circuit oscillates unexpectedly. What might be causing this and how would you fix it?

Common causes of unexpected oscillation:

  1. Positive feedback: Check for wiring errors that create feedback paths

  2. Parasitic capacitance: Breadboard capacitance can cause high-frequency instability. Add small capacitors (0.1 μF) across IC power pins.

  3. Long leads: Create inductance that can oscillate with circuit capacitance. Shorten leads and keep wires flat.

  4. Ground bounce: Insufficient grounding causes voltage fluctuations. Use multiple ground connections.

  5. Power supply instability: Ripple or noise on supply can cause oscillation. Add bypass capacitors.

Fixes: Add bypass caps, shorten leads, improve grounding, reduce stray coupling between input and output.

Summary

Laboratory skills transform theoretical knowledge into practical ability:

  1. Master your multimeter - Voltage in parallel, current in series, resistance with power off

  2. The oscilloscope is your eyes - Learn time base, vertical sensitivity, and triggering

  3. Function generators have 50Ω output - Account for this when connecting to circuits

  4. Use 10X probes by default - Higher impedance, lower capacitance, wider bandwidth

  5. Compensate your probes - Uncompensated probes distort square waves

  6. Triggering stabilizes the display - Set level, source, and edge correctly

  7. AC coupling removes DC - Useful for small AC on large DC levels

  8. Breadboards have limitations - High frequency and high current don't work well

  9. Loading affects measurements - High-impedance sources require high-impedance meters

  10. Safety first, always - Power off before connecting, respect voltage hazards

These practical skills take time to develop, but they're what separate theoretical understanding from real engineering capability. Every debugging session teaches something new, every measurement builds confidence, and every successful circuit build reinforces your knowledge. The lab is where you truly learn circuits—embrace the hands-on experience.