Temperature accuracy

Ruuvi products 🇬🇧 RuuviTag & RuuviTag Pro sensors
1

I am wondering about the temperature accuracy. On ruuvi.com I found the following

  • Temperature sensor accuracy
  • Typical absolute accuracy ±0,5 °C @ 25 °C
  • ±1 °C @ 0-25 °C
  • output resolution 0,01 °C

On bonsch-sensortech.com I found, for BME280 (in RuuviTag, right?)

  • 0.5 °C at 25 °C
  • 1.0 °C at 0…65 °C
  • 1.25 °C at -20…0 °C
  • 1.5 °C at -40…-20 °C

I had put the RuuviTag in my freezer, set at -18 °C, and the RuuviTag showed -28.5 °C. I thought the freezer’s thermostat should be more accurate than that, doubting the RuuviTag, but then another RuuviTag next to the first one showed -27 °C, making me wonder if the freezer has a problem.

I also found some old posts saying that the RuuviTag has a 5 °C accuracy at sub-zero temperatures but Bosch claims a better. I assume the to-be-launched RuuviTag Pro is more reliable, but what is the latest on RuuviTag temperature accuracy?

2

Hello,

Bosch datasheet is the authoritative document on temperature accuracy. We have some variants with SHTC3 and TMP117 sensors providing temperature data, but as far as I know every unit we have sold through webshop so far has BME280.

Placement of sensor in freezer and refrigerator makes a huge difference, and many coolers experience pretty wild temperature swings.

3

I just got a new Ruuvi pro. I took it out for a ride on my bike (dangling under the seat). All the weather apps in the area say it’s 86 deg F and Ruuvi says it 96 deg F. Part of the ride it might have been in direct sun, the other part it would have been in shade. I’ve recalibrated the device with a -10 deg F adjustment. My conclusion is that these things are wildly inaccurate out of the box. We’ll see if it’s more useful with the offset. (I am a bit skeptical, because the longer i used it the higher the temperature ran…from 96 to 98, while weather apps still showed 86).

4

I have a few Ruuvi Pros, and many regulars. I have never seen such a difference, when comparing them to one another. Either you have a faulty unit, possible but unlikely, or it is your test setup.

First, I would suggest that you make a better-controlled measurement, e.g., indoors. Also, it is good to remember that the Ruuvi tags do not react very fast to temperature changes, due to the sealed structure and mass.