Temperature sensor accuracy

Hi Nico,

If required, these types of boards are quite neat to act as a sort of semi-reference. The accuracy is claimed to be +- 0.1 degrees C within a certain range. I have an older model that claims +- 0.3 degrees C I think.

They can be accessed via Bluetooth on mobile, and can show historical data as well. Link: https://www.newark.com/sensirion/sht4x-smartgadget/ref-design-board-temp-humidity/dp/74AJ2003 

Thanks for pointing that out, that's really accurate!
That would solve the problem of which sensor to trust as a baseline.

A man with a watch knows what time it is. A man with two watches is never sure

I've added it to my wishlist

Thanks for pointing that out, that's really accurate!
That would solve the problem of which sensor to trust as a baseline.

A man with a watch knows what time it is. A man with two watches is never sure

I've added it to my wishlist

ntewinkel said:

that's really accurate!

Looks like the reference design module uses the SHT40 sensor

Looks like the accuracy takes a bit of a deviation at around the freezing point, which you are interested in.

For comparison, the performance plot for the DS18B20 sensor

From the specs the performance is not much better, it's just different, at zero degrees for the sensor. But I think the problem is, without a reference design, the discrepancy will easily exceed those charts (for instance having the sensor powered up will warm it, or if its on a board then other components or drafts will heat or cool it. I observed that with a SHTxx chip too, where my layout was not the same as the reference board, and the measurement was off by more than the datasheet curve (by about 1-2 degrees from memory). The Sensirion board is their reference design, so should be more accurate - hopefully!

Edit: This was my layout, but it was not fit for purpose, the measurement was off by several degrees. Subsequently I changed the board shape to more closely reflect the reference design, but I've not tried the new layout yet.

New layout:

shabaz said:

I changed the board shape to more closely reflect the reference design

A half-way house might be something more like this

https://sensirion.com/products/catalog/SHT85

Interesting! Thanks for that, beacon_dave , that gives me more confidence in the ds sensor I have…. I guess there’s no avoiding science class if I want to verify it  

I think shabaz ‘s suggestion is still going to be a very handy reference to have around, given that it’s a complete system and easily portable.

Without the reference design (or comparing against known temperatures) I would have had no easy way to know if my board had a discrepancy. Comparing to that, I could easily see my design had quite a large error. 

Also, it's worth maybe not powering the sensor permanently. My first board has 3.3V permanently applied, but that's unnecessary, it could be better powered from a GPIO pin, to reduce heating from the power source. 

Plus, location with respect to other parts. Actually now I look at my (still-incomplete) KiCad project folder, it looks like I aborted having that sensor on the board, i.e. I removed it for the revision 2, simply because of the poor performance in revision 1, after considering proximity to other boards.

ntewinkel said:

I guess there’s no avoiding science class if I want to verify it

Ah, now you are talking...

Dolbear's law
https://en.wikipedia.org/wiki/Dolbear%27s_law

Synthesize a snowy tree cricket chirp to attract snowy tree crickets; then sample their chirp and apply Dolbear's law to get ambient temperature.

Sorted...

PS you need to do this before the hummingbird actually eats the 'thermometer cricket'.

shabaz said:

Also, it's worth maybe not powering the sensor permanently.

I was thinking about that when in your previous comment you mentioned the sensor warming up...

shabaz said:

having the sensor powered up will warm it

I'm actually not sure how I have that set up right now. The DHT module is also housed in a little case. well-vented but not in the open like the ds18b20 probe.

I think, for my purposes, if I can at least get the two sensors to somewhat agree, and have them be somewhat accurate as to when I need to worry about things freezing, then that'll have to be good enough. I think aiming for 0.5 degrees will be enough there.

I'm planning to carve out some project time soon for this. So far this year there have been too many distractions! Looks like I have to replace an axle on an ATV tomorrow.. how did I get suckered into that?   

I think I've heard a few crickets recently... that'll give me a good starting point. easy peasy 

ntewinkel said:

I think I've heard a few crickets recently

I only have grasshoppers here...

ntewinkel said:

that'll give me a good starting point. easy peasy

This should get you going

https://vanhunteradams.com/Pico/Cricket/Crickets.html

ntewinkel said:

Looks like I have to replace an axle on an ATV tomorrow.. how did I get suckered into that?

Has someone been overdoing the rock picking recently perhaps ?