Temperature readings delayed

[londo]

Hello. I recently purchased a pack of RuuviTags, since based on the marketing they seemed ideal for my use cases. I’d like to use one to measure the temperature of a Sauna and another one to measure the temperature of a Palju (a hot tub).

I tried it and both seemed to work, with a couple of caveats that may make these tags not worth using after all.

First the palju sensor; I placed it inside a ziploc bag for some extra moisture protection, though I suppose this doesn’t help much with condensation. Based on reading the forums I kept the tag in for just a few hours. I think this might not be the best solution - connecting an external waterproof temperature probe could work better. I have zero electronics/soldering experience though, so this might prove difficult. Furthermore, keeping the tag resistant to the elements (e.g. it would still be outside while not floating in water) while having a wire coming out of the case seems impossible. Any ideas?

And second: my primary goal - the sauna sensor - proved to be pretty much useless. The idea is to get an alert when the room reaches a specific temperature, but since the sensor is inside the case and the air inside doesn’t seem to conduct heat very well, there’s a significant delay in getting the sensor to match the actual room temperature. So much so that the sauna is about 30-40 degrees hotter than the reading, which isn’t great. Using the tag without the case would probably help, but I doubt the tag would last very long. Is this problem solvable?

[otso]

Hello Londo,

@londo

First the palju sensor; I placed it inside a ziploc bag for some extra moisture protection, though I suppose this doesn’t help much with condensation. Based on reading the forums I kept the tag in for just a few hours. I think this might not be the best solution - connecting an external waterproof temperature probe could work better. I have zero electronics/soldering experience though, so this might prove difficult. Furthermore, keeping the tag resistant to the elements (e.g. it would still be outside while not floating in water) while having a wire coming out of the case seems impossible. Any ideas?

RuuviTag is IP67-rated, which means that it can be submerged briefly. Longer term submersion would void the warranty, but some people have been taping over the breathing sticker and enclosure opening to make tag more waterproof. I would also add a bag of desiccant inside the enclosure. Please note that leaving RuuviTag in water for long periods of time is at your own risk.

As for wiring external sensor, it would require some coding and soldering. I have modified some RuuviTags to have external sensors taking a normal USB cable, cutting the connectors off and using the 4 wires to carry power + data. I drilled a hole into enclosure and sealed it off with hot glue. Soldering to the test pads on bottom of RuuviTag is doable, but I’d practice a little bit on some prototyping boards before working on the tag. Here is one example by @jari.isohanni : Temperature measurement outside the tag

@londo

And second: my primary goal - the sauna sensor - proved to be pretty much useless. The idea is to get an alert when the room reaches a specific temperature, but since the sensor is inside the case and the air inside doesn’t seem to conduct heat very well, there’s a significant delay in getting the sensor to match the actual room temperature. So much so that the sauna is about 30-40 degrees hotter than the reading, which isn’t great. Using the tag without the case would probably help, but I doubt the tag would last very long. Is this problem solvable?

Placement of tag in sauna is critical for the temperature, @Scrin has been running the demo at lab.ruuvi.com for years and might have some advice.

[Scrin]

@londo

And second: my primary goal - the sauna sensor - proved to be pretty much useless. The idea is to get an alert when the room reaches a specific temperature, but since the sensor is inside the case and the air inside doesn’t seem to conduct heat very well, there’s a significant delay in getting the sensor to match the actual room temperature. So much so that the sauna is about 30-40 degrees hotter than the reading, which isn’t great. Using the tag without the case would probably help, but I doubt the tag would last very long. Is this problem solvable?

As @otso pointed out I have quite some experience regarding RuuviTags in Sauna. I’ve had a tag in my Sauna for over 3 years now, without enclosure, with typically one Sauna session a week, and no signs of problems yet.

I have written about these observations a few times before, here is a sample of my comparison with and without an enclosure, and a few words about “tag safety in sauna” on the next post right below the linked one. And here I wrote a few points about some of my observations regarding Sauna and RuuviTags

[londo]

Thanks for the quick responses.

@otso

I would also add a bag of desiccant inside the enclosure.

I’ll have to see if I have some desiccant bags in any packages, seems like I’d need to buy 10kg of the stuff to get it from a shop… Not having to deal with an external probe would be ideal, but like you pointed out, it might be a bit risky to try to jury rig a waterproof container that would also conduct enough heat to get an accurate reading.

@otso

As for wiring external sensor, it would require some coding and soldering.

I don’t mind the coding, and I can probably find a friend who is more in tune with a soldering iron. I’ll take a closer look at the link you provided and see if it’s worth trying out. I do have an extra tag, and I’m sure they’ll sell me more…

@Scrin

I’ve had a tag in my Sauna for over 3 years now, without enclosure, with typically one Sauna session a week, and no signs of problems yet.

I figured having a tag in the sauna without the enclosure would be doomed, but I suppose if it’s not at risk of water splashing, there’s not that much of a risk of humidity. I’ll have to give it a shot and see how it affects the delay. Your point in the other post about the tag being directly on a wall having an impact on the temperature may be worth considering as well, although the normal thermometer that’s on the wall seems to work fine regardless.

Any idea where I can buy those extended temperature range batteries? I’ve tried Googling but somehow I end up with a list of normal batteries.

[otso]

@londo

Any idea where I can buy those extended temperature range batteries? I’ve tried Googling but somehow I end up with a list of normal batteries.

Send an email to sales@ruuvi.com and we’ll figure it out. You can also find them from major business-to-business electronics distributors such as DigiKey, Farnell and Mouser as CR2477X, but there’s a lot of shipping restrictions on lithium batteries

[Kaaremi]

Here’s my sauna solution. I placed the tag add high as possible and about 1 cm from the wall. Material, the traditional laundry hanger. Now the delay is much less and is easy to adjust the alert with 5-10⁰C offset.

[salleq]

I’ve just set the temp alarm in sauna to be at the point the sauna is ready for me - it doesn’t really matter even if it’s much lower than the real temperature - as long as that temperature isn’t normally reached without the stove being on.