Sensors & transducers
How a temperature, a pressure or a heartbeat becomes a number: the transducer that converts physiology to a voltage, then the chain that digitises it.
In one line
A transducer converts one form of energy into another; a sensor is a transducer that turns a physical quantity — temperature, pressure, light, motion, bio-potential — into an electrical signal we can measure. Everything measured in digital health starts here.
How it works
A raw sensor signal is usually tiny and noisy, so a signal chain conditions it:
- Transduce — the sensing element changes an electrical property with the quantity (a thermistor's resistance with temperature; a strain gauge's resistance with pressure; an electrode's voltage with heart activity).
- Amplify & filter — an op-amp front-end boosts the signal and strips noise (mains hum, motion).
- Digitise — an analog-to-digital converter (ADC) samples the voltage many times a second and turns each into a number. Two knobs define the quality: sampling rate (samples/second — an ECG needs ~250–1000 Hz) and resolution (bits — more bits = finer steps).
Sensors you'll meet in health
| Quantity | Transducer | Device |
|---|---|---|
| Temperature | thermistor / IR | thermometer, incubator |
| Blood oxygen | LED + photodiode | pulse oximeter (SpO₂) |
| Pressure | strain gauge / MEMS | BP cuff, ventilator |
| Heart electrical | electrode | ECG |
| Motion / falls | MEMS accelerometer | wearable, fall alarm |
| Glucose | electrochemical | glucometer, CGM |
Where it goes next
The numbers an MCU collects become readings, then — once they leave the device — FHIR Observations with LOINC codes and UCUM units, the same data the interoperability labs work with. The hardware is where the data is born.
Watch for
Two numbers decide whether a reading is trustworthy: accuracy (closeness to truth) and precision (repeatability). Calibration and a clean signal chain protect both — a beautiful dashboard built on a poorly-conditioned sensor is still wrong.
Key takeaways
- A transducer converts energy forms; a sensor turns a physical quantity into an electrical signal — where all health data is born.
- The signal chain: transduce → amplify & filter → digitise (ADC).
- Sampling rate and resolution set data quality (an ECG needs ~250–1000 Hz).
- The numbers become FHIR Observations (LOINC + UCUM); accuracy + precision depend on calibration and a clean chain.
Check your recall
0 of 2 recalledActive recall beats re-reading — try to answer, then reveal.
Transducer vs sensor?
What's the signal chain from physiology to a usable number?