Abs Pressure
Measures pressure relative to a sealed vacuum reference (~zero Pa) at the sensor's reference port, outputting a calibrated digital reading from 1 hPa to 11,000 hPa typical, with 0.1 hPa resolution.
A silicon diaphragm separates the sensed pressure side from a hermetically sealed vacuum cavity formed by anodic bonding of a glass or silicon cap. Piezoresistors implanted in the diaphragm change resistance as the diaphragm flexes under pressure differential to vacuum. A Wheatstone bridge converts resistance change to mV; on-chip ADC and temperature compensation produce a calibrated I²C/SPI absolute pressure output.
In plain terms
Like a perfect 'sea-level' line drawn at the ocean's deepest trench bottom — every measurement above is referenced to vacuum, not to whatever the local weather happens to be.
Why designers use it
- Altitude sensing in phones, drones, weather stations — barometric absolute pressure is referenced to vacuum, not local air.
- Aerospace — cabin pressure, altimeters, and air-data systems require vacuum-referenced absolute pressure.
- Eliminate barometric drift — a gauge sensor fluctuates with daily weather; the absolute reading is pure altitude or chamber pressure.
- Tiny LGA packages (2 mm × 2 mm) drop into smartwatches and tablets without compromising real estate.
Best for
- Altimeters
- Smartphones
- Aerospace
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- Where atmospheric reference matters (tire pressure, hydraulic systems) — pull a gauge or differential sensor.
- For very high pressures (>10 MPa) — piezoresistive MEMS isn't designed for industrial process pressures; pull a thick-film or sapphire transducer.
Common mistakes
- Mounting the chip near a heat source — temperature drifts the output by tenths of hPa per °C if the calibration window doesn't match operating temps.
- Forgetting that the sensor's vent port (if any in absolute variants) is actually a process port — sealing it inverts the pressure reading.
Where you will find it
- A Bosch BMP390 24-bit absolute barometric pressure sensor in a Garmin Edge 1040 cycling computer reads altitude with 0.06 m resolution: the sensor's 0.4 hPa accuracy lets the rider see segment elevation change as small as a single floor of an apartment building during a Strava attempt.
- An Apple Watch Ultra's TDK InvenSense ICP-101xx barometric sensor enables dive-computer functionality — the absolute pressure reading lets the watch track depth to ±2 cm in saltwater alongside its dive-planning algorithms.
- A Boeing 737 MAX air-data module uses an Honeywell 24PCEF absolute pressure transducer for static pressure (altimeter) input: the sensor's vacuum-referenced reading is what tells the autopilot the aircraft's altitude during cruise without any local weather offset.
A short history
An absolute pressure sensor measures against a reference close to a vacuum, rather than against the surrounding air. This makes its reference independent of local atmospheric pressure. Absolute measurements are useful in applications such as altimeters and weather instruments, while the electrical output depends on the chosen sensor.