BME680 Bosch BSEC Library Calibration

Hello did some of you work with the BME680 and have a good way to calibrate Temp and Hum?

I just found a TempOffset in the library but im unsure on how to calibrate Humidity

Also a strange thing is, if i calibrate the temp with the "IceWaterMethod" (with distilled water) to be accurate on temp the humidity gets way more off (because its temperaturecompensated)

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Is borrowing a precision thermometer possible?

Relative humidity depends on the temperature! It should change with temperature, as far as I've got it.....

well no i dont have a precise thermometer but i thought the icewatermethod is even better because it always produces 0Celcius but i guess there is a possibility that i got it wrong (tho i repeated it too)

Maybe i need a 2 point temperature offset/slope to begin with? i just did a 1 point offset for 0 celcius, maybe its way off at 25 celcius because of that
the library doesnt offer that but i could program my own slope and always update the tempoffset in the library

I guess that would be the best way to solve the problem? make sure that temperature is always right (or nearly, its still just a 2 point offset slope) and THEN calibrate humidity to show the right value? (other way around would make no sense since its temperaturecompensated)

And then a 2 point slope for humidity? i wanna get accuracy to the MAX, i also did "salt" tests with pottasium and magnesium chloride, thats why i know humidity readings are to high

How did you immerse the BME680 into the ice bath? I'm assuming a plastic bag of some sort.

What was the tempOffset you measured?

yes with a "zip-bag", it was rougly -0,4 to reach 0 celcius on both BUT
with a salt test that should result at 84,6% both were measuring rougly 1% to much WITHOUT offset and rougly 4-5% to much with the right offset.. so either the icewatertest was wrong or the factory calibration was way off, or the offset just needs second point at 20-30 Celcius to compensate the non-linearity

Should i get a SHT-31 as "reference-sensor" ? its factory linearized 5 to 60 celcius to 0,3 Celcius tolerance (possibly better)

I've only had experience with the BME280 but should be the same.

Your temperature offset was -0.4 °C which means the sensor read +0.4 Deg when in the ice bath. I would think that is what I would expect from a ice bath. Maybe a little closer to zero but unless you have distilled ice and water and a lot of crushed ice and water in an insulated container, I wouldn't expect too much.

You didn't say what salt you are using. NaCl should be 75% humidity. And it takes a day or so to stabilize.

both were measuring rougly 1% to much WITHOUT offset and rougly 4-5% to much with the right offset

Where are you calculating in the temperature offset? At the raw temp, or after temperature is calculated?

If at the raw temperature, I don't think that is valid as the factory calibration coefficients result in a non linear compensation.

Well thats the problem i have, is the icebath "really" at exactly 0,0, atleast i hope so but it could be at 0,4 and the sensor was right from the start

pottasium chloride for 84/85%
magnesium chloride for 33%

The bosch bsec library can take a temp offset i just feed it to the library, but i could try a 2 point mapping of the offset and always update the value to the library

but im also wondering why the bsec library cant take humidity values or maybe i missing something

Unless you have a source for a more precise temperature I'm guessing you will have to suffer with what the basic BME680 tells you. I know its frustrating but I've found after moving on to something else the frustration fades.

Or you could try to create the triple point of water.

Or take up meditation.

Well the question wasnt about how to get it right but how to do it "theoretically" right

Is a 2 point offset with a precise reference thermometer the way to go? same for humidity?

And the main question remains, how i compensate for humidity in the bsec library by bosch

even if i calibrate the wrong zero point but still calibrate humidity, if it in the end shows me +/- 0.5-1% humidity right im happy

Does that mean i cant improve accuracy further myself?

No, but I suggest you don't apply any factors to temp Raw or anything Raw (i.e. before they have the polynomial factor applied). If this is/was what you were doing,

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