Calibration

Calibration is the process of adjusting a measuring instrument so its readings correspond to the actual values of a physical quantity.

Discover FizziQ

How to measure it in class

Steps:

Open FizziQ and select the atmospheric pressure sensor. Note the displayed value at ground level.
Go to a known floor height (approximately 3 m) and note the new pressure value.
Compare the measured pressure difference with the expected theoretical value (approximately 0.36 hPa per 3 m of altitude).
Discuss the observed difference and determine if the sensor needs adjustment or if precision is sufficient for the planned experiment.

Scientific activities on this topic

Several experiments easily performed with a smartphone, tablet, or computer allow you to understand the challenges of calibrating measurement instruments.

1: Evaluating Sensor Quality - Analyzing sensor precision: https://www.fizziq.org/en/activities/evaluate-the-quality-of-a-sensor/
2: Uncertainty - Analyzing measurement uncertainties: https://www.fizziq.org/en/activities/uncertainty/
3: Altimeter - Creating an altimeter with an atmospheric pressure sensor: https://www.fizziq.org/en/activities/altimeter/

Learn more

Origin and history of calibration

Calibration is as old as metrology itself. Since antiquity, merchants used standard weights to verify their scales. In the 18th century, the creation of the metric system in France imposed universal standards. Today, the International Bureau of Weights and Measures (BIPM) coordinates reference standards worldwide.

Digital sensor calibration

MEMS sensors in smartphones (accelerometer, barometer, gyroscope) are factory-calibrated, but this calibration can drift with time or temperature. In laboratories, standardized protocols (ISO 17025) ensure measurement traceability. Digital calibration often relies on polynomial models stored in the sensor firmware.

Orders of magnitude

Smartphone pressure sensor drift is typically around ±1 hPa. A calibrated laboratory thermometer achieves uncertainty of ±0.01°C. Atomic clocks, the most precise time references, drift only one second in 300 million years.

Advanced applications

In medicine, calibration of imaging equipment (MRI, CT scanner) is essential for reliable diagnostics. In industry, calibration of measurement chains ensures production quality. In space research, onboard instruments are calibrated before launch and recalibrated in flight using reference targets.

Formula

For linear calibration: V_corrected = a × V_raw + b

Where:

a: slope coefficient
b: offset in the measured quantity’s unit
V_raw: value read on the instrument
V_corrected: estimated actual value

Application examples

Zeroing a scale before weighing an object
Adjusting a medical thermometer with an ice-water bath at 0°C
Calibrating a smartphone touchscreen during first use
Adjusting the light sensor of a digital camera
Verifying a pressure gauge with known atmospheric pressure

FAQ

Q: What is the difference between calibration and standardization? A: Calibration includes adjusting the instrument, while standardization only compares measured values to a standard without modifying the device.

Q: How often should an instrument be calibrated? A: This depends on the instrument and required precision. In class, verification at the beginning of a session is generally sufficient.

Q: Can smartphone sensors be calibrated? A: You cannot directly modify the sensor, but you can apply a mathematical correction to raw data using FizziQ.

Q: Why is calibration important in science? A: Without calibration, measurements can be systematically biased. A calibration error affects all results.

Q: Is a well-calibrated instrument necessarily precise? A: No. Calibration corrects systematic errors but does not eliminate random errors related to measurement noise.

Precision - Resolution - Measurement noise - Uncertainty - Sensor - Metrology