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Sensor related question, BME280

Hi there,

for monitoring air pressure, temperature and (relative) air humidity, I purchased a few "breakout boards" carrying Bosch BME280 sensor.

There are several models out there with different board layout, most of them from China.

So, to monitor those envirmonment values I have several Raspberries where each one is connected to a BME280 via I2C. Same worked with Arduino formerly, but I want them to be connected via internet / wifi.

Nothing special. Yes?

Well, what I am wondering about is, that temp. and pressure are very similar on every board, but not so the relative humidity.

Most significant "outlayer" is produced by Adafruit BME280, which claims that the humidity value is around 10 percent points higher than most other sensors (i.e., 40% China noname and 50% Adafruit). There was no difference whether connected one after the other, or both, Adafruit and China noname on the same bus with different addresses.

I think, assuming that Adafruit's values are the most precise ones, just because this is the most expensive one, is a little too naive :-)

Any experiences with that stuff, or knowing ways to test / verify / calibrate those modules?

Best regards,

Markus

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Reply to
Markus Robert Kessler
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Yes. humidity mearuement is guesswork and approximate at best, whatever consumer grade stuff you use.

There are some manuals describing closed containers and salt solutions at given concentrations. Are you sure, it's worth it?

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Reply to
Axel Berger

Ideally, you?d measure the humidity at three or more points, say, the minimum likely value, the maximum likely value, and the midpoint. This would provide for linearity correction as well as calibration. Since calibration often varies with temperature, similar variation of temperature is also needed if accuracy is important.

The humidity can be measured directly from wet-bulb and dry-bulb temperature readings, assuming a sufficient volume of air to make the measurements.

For a single-point calibration, I?d use the air in the room, and compare with a wet/dry-bulb psychrometer.

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Reply to
Michael J. Mahon

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