Bluetooth Temperature Logger?

I just found the Kestrel Drop – the D3 looks very interesting..
Any opinions?

great!  thanks!  now I’m getting ads for Kestrel Drop : )

actually, that looks pretty nice if there was something I wanted done with it.  Maybe log the temperature for an entire week trip and then download it when I get back.

I like how the temperature sensor appears to be a little bead suspended from a wire so it quickly stabilizes.  My temperature sensor is buried inside the instrument and takes 30 minutes for the temperature to stabilize.

Yeah they look quite good. http://www.weatherflow.com/products/ might also be an option but there is not too much information about it.

I will probably get a Drop D3. I saw the Kestrel 5000 series are also available with the Bluetooth link – the only difference between 5000 and 5500 seems to be the included vane?
But I don’t want to leave a device like that outside..

I’ve got the D3 now, and I have to say it’s really nice for the purpose outlined in my previous posts!

Always the same story:

Out of interest I compared the Kestrel Drop D3 to two other sensors I have, a TS34C (weather station) and a Bosch BME280.

As expected I get 3 different values, from coldest to warmest: Drop D3, TS34C, BME280 – with the difference between the D3 and BME280 being around 1 degrees. Both the Kestrel as well as Bosch should be rather accurate..

Christoph,
You said, “Both the Kestrel as well as Bosch should be rather accurate”. I haven’t tested the Bosch temperature sensor but I did test the Kestrel temperature sensor (D2 model). The reference thermometer I used was a (FLUKE 1551A Ex) with a current NIST calibration certificate.
At an actual temperature of 71.7F, the Kestrel read 72.8F (+1.63 F or .73 F worse than the error specification of +-.9F).

You can always calibrate it in a glass full of ice, then fill up with water.  Put sensor in between ice cubes in the middle.  That should be pretty close to freezing at sea level.  If sensor isn’t waterproof put in a plastic bag.  Let it sit for 15 minutes to make sure it stabilizes.

@Richard Nisley, I wish I had a reference like that, but unfortunately that’s too expensive for hobby use.

With “should be rather accurate” I was only referring to the specs (which are usually very optimistic) and the experiences I found on the web.

Regarding cheap sensors, there is an interesting page here: http://www.kandrsmith.org/RJS/Misc/hygrometers.html with a lot of data.
He states that the BME280 always showed the highest temperature, which might be due to a different sensor technology and it’s case/board. This is also what I get.
The Kestrel has an external sensor, so it shouldn’t be affected by any kind of case or similar.

I’m just quickly comparing numbers though, not taking into account humidity and other factors. I will add a bunch of other cheap sensors (SHT71, DHT11, DHT22) I have lying around and see how they compare.

My biggest problem – as always – is that I don’t have a reference thermometer.

@Richard Nisley, as you have quite a lot of experience with these things, is there a test (like Jerry posted) which is accurate enough to calibrate a thermometer? I’m not sure if using ice cubes is enough to calibrate it, given that if you use a bunch of sensors the difference is already smaller than 1C.

“That should be pretty close to freezing at sea level.”

True.  Ice water is pretty close to 0C ANYWHERE because it is a very weak function of pressure.  Unlike boiling, which is moderately strong function of atmospheric pressure (e.g. 212F at sea level, 198F at 7500 feet).

Christoph,

Jerry described the “triple point” calibration method which is an accurate calibration method for sensors primarily used near freezing. If all of the sensors varied linearly with the “triple point” calibration that would make things easy, but many of them don’t.

or, if there’s an offset the triple point cal would work

or, us people that go out into the wilderness maybe care most about temperatures near freezing.  Like, will my water filter or drinking water freeze.  Or, will my sleeping bag be warm enough – most people sleep in low temperatures within 10 or 20 F of freezing.

>“triple point” calibration method”

But the triple point of water occurs at 32.01F (that’s easy) and 4.58 mm Mercury (not so easy).  A rough estimate of that pressure (using paper and pencil) gives me an altitude of about 25 miles (or a vacuum chamber in a lab).

But really, is there that much difference between 32F and 32.01F?  That was a my point – the temperature of ice water is very insensitive to pressure.

Now we’re getting back to the geeky BPL of times past!

Thanks a lot guys, I’m right now thinking of getting a better Temperature sensor (if possible with Hygrometer) but it’s quite difficult to evaluate reliable ones or distinguish them. I looked at the Fluke 53II B which sometimes available as used on ebay, but have to read a bit more on this topic first.