Sensors and Signal Conditioning

Overview

Overview of resistive, capacitive, and active sensors, Wheatstone bridges, excitation methods, and low‑noise front‑end design for accurate measurement systems.

Prerequisites

• Basic circuit analysis and op‑amp knowledge

Learning objectives

• Choose suitable excitation and conditioning for common sensors (strain gauge, thermistor, photodiode)
• Design low‑noise amplifiers and implement proper filtering for sensor outputs
• Understand calibration and temperature compensation basics

Hands-On Mini Task

1. Build a Wheatstone bridge with a strain gauge and amplify the differential output using an instrumentation amplifier. Measure sensitivity and noise.
2. Implement simple calibration by measuring known loads and fitting a linear correction.

Expected result: measurable bridge sensitivity with SNR sufficient for the target measurement range.

Sensor interfacing notes

• Excitation: use stable current sources or ratiometric measurement for bridge sensors to reduce sensitivity to supply variation.
• Input protection: clamp diodes and input resistors help against transients when interfacing real-world sensors.

Worked example — photodiode front end

1. Use a transimpedance amplifier (TIA) with feedback resistor chosen for desired gain. Add feedback capacitor to control bandwidth and stability.
2. Measure noise current and compute minimum detectable signal given bandwidth and resistor thermal noise.

Troubleshooting

• If sensor output is noisy, check grounding and routing; move analog input paths away from digital switching sources.

Navigation

• Previous: Active Filters Workshop
• Next: Instrumentation Basics