Humidity calibration accuracy

Hello,

I tried to calibrate humidity measurement following this topic https://blog.ruuvi.com/humidity-sensor-673c5b7636fc and the measurements I receive are around 69%, 70% and 69% and temperatures 23,7 - 23,9 C. I tried several different containers, with and without lids, different amount of salt and water, and still the humidity is always between 68 - 71% even after keeping the container unopened for several weeks. The real humidity should be 75%, so is the difference still within normal variations and within RuuviTag’s measurement accuracy and therefore safe to calibrate all tags to 75%, or should I calibrate them to a bit lower value?

Using iOS ruuvi app v. 0.5 (19), tags running in firmware 3.28.12

Thanks, Mikko

Hello,

It’s ok to calibrate the tags to 75 %. Please note that the calibration is on the app, so other devices will still read uncalibrated values.

Thanks Otso, will do so. I was thinking that something in my test setup was not ok, as the stated accuracy is -3… +3%, and these were +7 off.

Mikko

I am revisiting the calibration issue again, since it becomes more clear I need a solution for calibration rather sooner than later.

I have 20+ RuuviTags and I am about to order a few more. To give you an example, two of my RuuviTags purchased in November 2019 read the following (in same enclosed 0.5L container with humidity control pack for past few days):

Tag - Temp - Humidity
r1 - 22.0C - 51%
r2 - 22.1C - 61%

Real humidity is 65% (65% humidity control pack).

In fact, probably none of my RuuviTags are within the +/- 3% outlined here but they are partially 1-2 years old (indoor use only). (I’ll purchase some BE280 and connect them to a Pi etc to gather some more data over the next few months).

I assume the firmware version (I never updated) has no relation to the accuracy of humidity measurement?

Is there an “official” Ruuvi effort for integrating calibration?

Does calibration via Firmware (update?) make sense?

I originally planned to customize RuuviCollector in the next few weeks as this is how I collect my data, but I’d like to hear some more feedback before I settle for that.

PS: Apologies if I should have opened my own topic.

Hi Alex,

No worries, there can be new topics :slight_smile: . We have had discussion with Bosch regarding humidity accuracy and so far each device which has been showing “wrong” values have been tested to be OK. Did you open enclosures or were the enclosures closed during this testing?

Please note also that in Bosch data sheet ±3% difference is typical accuracy and there can be some devices where accuracy range is wider (e.g. ±6%).

I assume the firmware version (I never updated) has no relation to the accuracy of humidity measurement?

  • Firmware version doesn’t have impact.

Is there an “official” Ruuvi effort for integrating calibration?

  • Humidity calibration is possible in Android beta version and we are planning to publish this soon to all users. We are planning also to improve this feature.

Does calibration via Firmware (update?) make sense?

  • It could make sense and we will see how we can improve calibration feature.

As the difference is very big in this one device we would like to change the device to another one and test in our lab. Could you send email to henri@ruuvi.com with your address.

Has anyone ever validated to use of a single additional correction factor across a range of conditions not at a calibration point?

One solution (which depends on use case) is to implement “final” adjustment post transmission and post storing. That is, receive the “preliminary” values and insert them in to the data store. Then provide a “final” adjustment before analysis. This has the advantage of being able to refine that adjustment at a later date but the disadvantage of needing to be implemented in each use case.

Please see/revise my discussion at https://github.com/ruuvi/ruuvitag_fw/wiki/FAQ:-Temperature,-humidity-accuracy