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Sensor comparison: temperature, humidity and air pressure

How well, or how differently, do different sensors measure environmental data? A comparison of two units under different conditions.

Reliable data for temperature and humidity
Environmental data can be very helpful, but for that they should also be reliable. Room temperature and humidity, for example, affect not only our health and well-being, but also the preservation and structure of the building and furniture. That’s why thermo-hygrometers are becoming increasingly popular. But if the instrument shows wrong values, then it can be bad not only for health, but also the structure of the building.

A relative humidity of 40% – 60% and a room temperature of 18°C – 22°C are mostly perceived as pleasant. The optimal values vary depending on the room (Living room, bedroom, bathroom, kitchen, etc.) The room temperature can be easily adjusted via the heating in the apartment. The room temperature is also relatively easy to feel without the need to measure it precisely. Humidity is not so easy to sense and also not so easy to regulate. There are many tips on what methods can affect the humidity in the apartment, but you need a meter to measure it. In the DIY and IOT field, there are numerous sensors for this task. For a small amount of money (less than $10), you can get sensors that promise high accuracy. If these sensors are as accurate as they promise, then they should show identical values for a simultaneous measurement at the same location, right?

Sensors used in this test
I own a (non expensive) digital thermo-hygrometer and my analog living room barometer also has a temperature and humidity display. I found two different sensor modules in my M5Stack pool: The first generation of ENV unit with DHT12 and BMP280 sensor and the current version ENV III with SHT30 and QMP6988 sensor.

The BMP280 and the QMP6988 sensor are digital air pressure sensors. The DHT12 and SHT30 sensors are humidity and temperature sensors.”

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