BME680 temperature offset impacts the humidity

ESPHome
1

Hello,

after I added an offset to the temperature of my BME680, I noticed it impacted all the readings of the BME680

in the graphana below you can see that at the moment I implemented the offset, the humidity increased and there is a spike on the CO2 equivalent and the IAQ. Although the last two appear to have reconverged, the humidity is still 20% above

image
image1656×739 77.1 KB

here is my code


i2c:
    sda: D1
    scl: D2
    scan: True
    frequency: 8khz

bme680_bsec:
    # i2c address
    # -----------
    # Common values are:
    # - 0x76
    # - 0x77
    # Default: 0x76
    address: 0x77
    temperature_offset: 3

sensor:
  - platform: bme680_bsec
    temperature:
      name: "DanielOffice_BME680_Temperature"  
    pressure:
      name: "DanielOffice_BME680_Pressure"
    humidity:
      name: "DanielOffice_BME680_Humidity"
    iaq:
      name: "DanielOffice_BME680_IAQ"
    co2_equivalent:
      name: "DanielOffice_BME680_CO2_Equivalent"
    breath_voc_equivalent:
      name: "DanielOffice_BME680_Breath_VOC_Equivalent"
    gas_resistance:
      name: "DanielOffice_BME680_Gas_Resistance"

Any clue on how to resolve this ?

thank you

Luj

2

The only way I am aware is to use a sensor filter to alter the output but I’m at a loss as to how to calibrate it accurately and do not know if it should change dynamically across a range of temperature/humidities.

3

Relative humidity depends on Temperature.
You can apply offset in sensor as a filter, it will mnot affect BME680 logic.

4

I believe that humidity in the BME680 is dependent on temperature; from memory it is one of the calibration inputs.

I bought a handheld temp and humidity device to calibrate environmental sensors. I have found the biggest element is the position of the sensor in a room; outside/ internal wall, ceiling, cupboard side etc.

5

I’d be keen to hear a bit more detail on your findings for this if possible.

6

I have found that this sensor is wildly inaccurate in relation to another sensor that is placed right next to it (Eve room sensor). I think that the BME680 is just simply not an accurate sensor device and I think I will get rid of it soon unless I find a thread somewhere where I am proven wrong in my opinion.

7

" Relative humidity (RH) (expressed as a percent) also measures water vapor, but RELATIVE to the temperature of the air. In other words, it is a measure of the actual amount of water vapor in the air compared to the total amount of vapor that can exist in the air at its current temperature ."

Trying to say: device will recalc relative humidity when offset applied.

8

Little bit about accuracy.

Screenshot I2C_sensors_comp
Screenshot I2C_sensors_comp1192×731 122 KB

Here can see 4x sensors data located in same place. First one is Sonoff TH01 Zigbee devices, others names You can see on screenshot - all connected to same ESP32.

9

Don’t sure this is the same, but I have a DHT11-sensor that has about 2° fault.
I want to offset that, but don’t know how to add an offset to the sensor?

Is this what you do also?

11

I got my answer here:

Offset a sensor

12

A man with one clock always knows what time it is. A man with two is never really sure.

The BME280 is known for self-heating. I suspect the BME680 is similar. Neither are know to be really accurate, but do generally meet their accuracy spec.

If you want to go down the rabbit hole of more accurate measurements, I suggest starting here to see what is in store for you: