Wrong RTH reported value from ruuvi unit

#1

Hi,

I’ve had 3 ruuvi units for some time already, bought them during the initial kickstarter.
However, since half a year ago one is consistently reporting the wrong humidity value. They all haven’t ever been used outside, and I installed fresh batteries recently.
Present fw is 1.2.12, successfully installed via Nordic app as zip package.

Here’s what I read, after placing them on the table, next to each other, covers are taken off:
R1: 21.99C 40%RTH 1012.36hPa
R2: 21.88C 38.50%RTH 1011.38hPa
R3: 21.85C 59.50%RTH 1012.68hPa

Any idea how to fix this?

Thank,
Rob

1 Like
#2

Hi Rob,

Seems bit strange but it’s possible that there’s some issue with BME280. First you could do two different things. Add them to closed plastic case with small bowl of warm water. Then see if the humidity rises in all devices to 100%. Then if possible to add them to very warm place where humidity can go to very low level. Then see if this is changing the calibration levels of BME.

If that doesn’t help lets find some other solution.

Br. Henri

#3

hi Henri,

Just followed your advice.
First when in moist environment, it showed 39C and 100%rth.
Then I gently heated it up with a solding hot air station. This time it went as high as 87C and max 40%Rth.
Overall, this did not solve the problem, it is still showing the delta as earlier described.

Let me know.

BR,
Rob

#4

Hi Rob,

Ok, please send email to henri@ruuvi.com and let’s figure out how to take next steps.

Br. Henri

#5

I have a similar case. Got 3 ruuvis, ordered first day of release in Finland. Running them all 3 next to each other (open case a few hours) gives following results:

R1: 24.46C 35.00%RTH 1015.43.36hPa
R2: 24.54C 26.00%RTH 1014.28hPa
R3: 24.52C 26.50%RTH 1014.58hPa

I tried reflashing R1 but it seems it is always offsetted almost 10% of RTH from the others. Should I assume this one is bad?

#6

We have discussed regarding this topic with Bosch and their data sheet is giving typical accuracy of ±3%RH and hysteresis ±1%RH. However according to normal distribution curve there can be a certain amount of devices which can have lower and higher accuracy. It means that there can be a very little amount of units where sensor accuracy can be ±6% or even ±9% (or something between these). These values are no visible on official data sheet but should be valid according to our discussion.

In cases where sensor as been more accurate in past it might be also that sensors is broken from reason or another.

Even that Bosch is not recognizing these under their warranty we will review these case by case.

#7

The BME280 Data sheet 4.2 states “each sensing element behaves differently.”
Table 16 shows five Humidity related trimming memory locations. Section 4.2.3 provides code for utilizing.

The ruuvi firmware drivers/bme280/bme280.c includes this code.

Is the purpose of this seems to be to compensate for individual sensor variations.

What Is missing??

Reference: https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME280-DS002.pdf