Electronic Weather Instruments
How a weather station senses temperature, humidity, pressure, wind and rain, and why where you put it matters.
The question
Two thermometers on the same street show readings 5 degrees apart. Which one is right?
What you’ll discover: how electronic sensors measure weather, how official stations are set up in Canada, and how to check whether your sensor is telling the truth.
In simple terms
BeginnerA sensor for each kind of weather
- Temperature: a thermistor (Lesson 12) or a digital sensor chip changes with heat.
- Humidity: a tiny capacitor (Lesson 8) whose insulating layer soaks up water vapour from the air, changing its capacitance.
- Air pressure: a microscopic flexible membrane on a chip bends as the air pressure changes.
- Wind speed: spinning cups (an anemometer) carry a magnet past a sensor, making one pulse per turn. More pulses per second means more wind.
- Wind direction: a vane that points into the wind, with sensors that report its angle.
- Rain: a tipping bucket gauge: a little see-saw fills with rain, tips, and empties. Each tip makes a pulse and stands for a small, fixed amount, often 0.2 or 0.25 mm.
Where you put it matters
Most bad weather readings come from where the sensor is, not the sensor itself. Environment and Climate Change Canada’s guidelines for climate stations put the thermometers:
- in a white, louvred shelter that shades them from sun and lets air flow through,
- between 1.25 and 2 m above the ground, over short grass,
- away from trees and buildings by at least twice their height.
A thermometer in the sun, on a south wall, or above a driveway can read many degrees too warm. At home you rarely have that much space, but you can still shade the sensor, keep it away from walls and pavement, and let air move around it.
Wind sensors work best high up and clear of obstacles (official stations use 10 m), and rain gauges must be level and away from roofs and trees that block or drip.
Go deeper
IntermediateAccuracy, resolution and calibration
A display that shows 21.37 °C (70°F) has a resolution of 0.01 °C (32°F), but that doesn’t mean it’s accurate to 0.01 °C (32°F). Check the datasheet: a common digital temperature sensor like the DS18B20 is specified to ±0.5 °C (0.9°F) over −10 to 85 °C (14°F to 185°F), and less accurate outside that range.
Calibration means comparing a sensor with something you trust. A classic check is an ice bath: a glass packed with crushed ice and topped up with cold water, stirred and left a few minutes, sits very close to 0 °C (32°F). If your sensor reads 0.4 °C (33°F) there, you know its offset at that temperature.
AdvancedSensors drift, and stations fail
Sensors change over time: humidity sensors drift, especially after years of dust and condensation; anemometer bearings wear and slow down; rain gauges clog with leaves or bird droppings and miss rain. Snowfall is notoriously hard for a tipping bucket, which needs the snow melted first.
That’s why it matters to know the difference between an educational or home station and a calibrated official observation. A home station can be very useful for seeing local patterns, especially when it’s well placed and regularly checked against a trusted reference. Compare your readings with Environment and Climate Change Canada’s official Lethbridge Airport observations, or with the well-sited home station on Lethbridge Weather, and look for consistent differences.
Quick check
How does a tipping bucket rain gauge measure rain?
A small see-saw fills, tips and empties; each tip is a pulse that stands for a fixed amount of rain.
How high above the ground are official climate station thermometers in Canada?
Between 1.25 and 2 m, over short grass, in a shaded, ventilated shelter.
What is the difference between resolution and accuracy?
Resolution is the smallest step a display shows; accuracy is how close the reading is to the true value.
Words to know
- Anemometer
- An instrument that measures wind speed.
- Calibration
- Checking or adjusting a sensor against a trusted reference.
- Drift
- A slow change in a sensor’s readings over time.
- Radiation shield
- A shelter that shades a temperature sensor while letting air flow.
Learn more
- Environment and Climate Change Canada: measuring temperature: how official climate stations place thermometers
- Hands-On Weather Science: weather experiments for kids
- Lesson 12: Sensors
- Next: Data logging
Electronics School is part of the Discovery Zone. Every activity here runs on small batteries or a USB cable: never wall outlets. The one plug-in tool is the optional soldering iron, set up by an adult.