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The common sensor families

How common sensors for temperature, motion and sound work, and what limits each one.

Core

Read firstWhat a sensor actually isAnalog-to-digital conversion
The common sensor families for temperature, motion and sound Temperature: a Pt100 RTD is 100 ohms at 0 °C and rises almost linearly with temperature; an NTC thermistor falls steeply and non-linearly; a thermocouple makes a voltage from the temperature difference between its junctions. Motion: accelerometer, gyroscope and often a magnetometer. Sound: a digital MEMS microphone sends PDM or I²S to the host. Temperature Pt100 RTD 100 Ω at 0 °C resistance vs temperature Platinum; standardised in IEC 60751 NTC thermistor resistance vs temperature Falls steeply, non-linearly; linearised in software Thermocouple V junction cold junction Seebeck effect: a voltage from the temperature difference Needs cold-junction compensation Motion MEMS inertial sensors Accelerometer linear acceleration, including gravity Gyroscope angular rate; orientation drifts without correction Magnetometer often added for heading Sound MEMS microphone audio arrives digitised PDM or I²S Host decimates or receives it
Temperature is sensed by RTDs, NTC thermistors or thermocouples; motion by MEMS accelerometers, gyroscopes and magnetometers; sound by digital MEMS microphones.

Key points

  1. A Pt100 platinum RTD has a resistance of 100 Ω at 0 °C that rises almost linearly with temperature; its resistance-temperature relationship is standardised in IEC 60751.12
  2. An NTC thermistor's resistance falls as temperature rises, steeply and non-linearly, so readings must be linearised in software, for example with the Steinhart-Hart equation, a polynomial fit or a lookup table.3
  3. A thermocouple generates a voltage from the temperature difference between its junctions (the Seebeck effect), so it needs cold-junction compensation to report an absolute temperature.4
  4. MEMS inertial sensors combine an accelerometer (linear acceleration, including gravity) and a gyroscope (angular rate); a magnetometer is often added for heading. Gyroscope readings integrate into orientation that drifts over time without correction.5
  5. Digital MEMS microphones commonly output PDM (pulse-density modulation) or I²S, so the audio arrives already digitised and the host only decimates or receives it.67

Where to go next

Sources

  1. IEC 60751:2022 Industrial platinum resistance thermometers and platinum temperature sensors · IEC · Standard
  2. A Basic Guide to RTD Measurements (SBAA275A) · Texas Instruments · Reference
  3. Methods to Reduce Thermistor Linearization Error, Memory, and Power Requirements Over Wide Operating Temperature Ranges (SNOAA12) · Texas Instruments · Reference
  4. A Basic Guide to Thermocouple Measurements (SBAA274A) · Texas Instruments · Reference
  5. BNO055 Intelligent 9-axis absolute orientation sensor datasheet (BST-BNO055-DS000) · Bosch Sensortec · Datasheet
  6. MEMS Microphone Direct PDM Input via I2S to a C5515 EVM With Software Decimation (SPRAC51) · Texas Instruments · Reference
  7. ICS-43434 Multi-Mode Microphone with I2S Digital Output datasheet (DS-000069) · TDK InvenSense (copy hosted by distributor CDI) · Datasheet