Outdoor sensor and optimal placement

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weatherguy112
Posts: 3
Joined: 01 Aug 2015, 03:21

Outdoor sensor and optimal placement

Post by weatherguy112 » 01 Aug 2015, 03:54

Looking for a little feedback (from other users or from the folks at Netatmo) on optimal placement of the outdoor sensor.
Have read what's in the manual and it seems no matter where I try it outside of my house I'm generally 2-4 degrees (celsius) higher than what a nearby official weather service has our temperature at. I've read some reviews where some people seem to say that the sensor just isn't capable of putting out accurate readings, but hope springs eternal. There are a couple of independent Netatmo stations on the map within about an hour of where I am that seem to have temperatures that are more consistent with what our weather service's data shows for my city, so am hopeful that it's possible that with some tweaking I can have numbers that can be relied on.

I've tried mounting directly under the soffit in a dry and sun-free spot and have moved it around to a handful of different places on the North, East and South sides of my house. Have tried mounting to my deck about a 6 feet away from the house and in a shaded/dry area. All to no avail.

Other info that may or may not be relevant:

- Our official weather service takes its readings at our airport, which is 5km outside of the city or about 15 km from the house where I have the Netatmo station setup.
- Elevation at the airport is about 10 meters higher.
- The other Netatmo sensors I'm comparing to are in much smaller towns or even in the country
- I live in a city of about 50,000. Have read that there can be a heating effect in bigger cities, but don't think that applies to a city this small?
- Mounting in each instance is done with a screw put into a board or a small bracket that's directly against the house underneath an overhang, then sliding the sensor over top of the screwhead so that it's hanging and resting against the house (or in the case of the deck, against a board).
- Accuracy seems to be somewhat better (like only 1-2 degrees high) in the early morning hours and appears to get worse with daytime heating (2-4 degrees) and continues into the evening. The last two evenings things have gotten even further out of whack around sunset with the station having readings as much as 6+ degrees celcius higher! That huge variance seems to slowly come back down to being 1-2 degrees off by morning.
- The outdoor sensor's humidity during the day has been in large part within respectable bounds compared to the weather service's reading however as I type this right now with the sun going down the outdoor sensor is showing my temperature as 6 degrees higher the humidity is a full 30% lower on my weather station compared to what the weather service is showing.

In your experience what have you learned to be the optimal place to put the outdoor sensor?
Have you noticed any places that force readings to be particularly bad?
Any mounting setups that can make or break readings?
Is it at all possible for there to consistently legitimately be this large of a variance in a small geographical area?

Thanks for any help or tips you can share!

jev
Posts: 21
Joined: 23 Mar 2015, 10:27

Re: Outdoor sensor and optimal placement

Post by jev » 04 Aug 2015, 16:20

Assuming you are on the northern hemisphere, it would be best to place the sensor on the north wall of your house. Be aware however that (brick) walls and wooden (stone or sand even worse) floors *will* heat up during the day and play havoc with both, temperature and humidity readings. If you have the sensor close to an overhanging roof, you will get even higher temperature readings since the heat is trapped underneath the overhang.

The absolute best would be to hang the sensor in a white painted, half-open cabinet that allows wind to pass through, placed on a large lawn:
Image
As you can see, these cases have a lid that allows hot air to escape instead of building up inside.

I hung my sensor in a half-open cabinet, mounted it facing north to the fence where it is mostly overgrown by grape-plants. In the early morning, sun is still heating up the cabinet, causing it to measure up to a full degree higher than it should be. I drilled a couple of holes in the sides near the top of the cabinet to let the air flow a bit more which seems to have helped a bit. For testing purposes, I "built" a larger cabinet and mounted it on an old tripod. I placed it on the grass, a good 10 yards from the house and shed (got a small garden, so I couldn't place it further away). The readings where quite good (they behaved close to professional weatherstations around me with slightly different readings that could be explained by environmental effects). Unfortunately, the whole installation was neither nice nor sturdy so it had to go before a storm would take it.

Living in a city (even a small one) may also affect temperatures, that is not because of a false reading but because it actually is hotter in the city than on the countryside. Less wind, more heat-reflecting or even heat-collecting surfaces, more heat production from households and traffic.

andpotti
Posts: 121
Joined: 12 Jun 2013, 11:48
Location: UK

Re: Outdoor sensor and optimal placement

Post by andpotti » 04 Aug 2015, 19:57

This is my outdoor setup, a simple radiation shield bought second hand from eBay, the sensor fits perfectly inside. checked and calibrated against surrounding airports using their live wx data and 2 local davis systems. I am 100% happy the temp is spot on come rain, shine, or cold.

£5 well spent.
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andpotti
Posts: 121
Joined: 12 Jun 2013, 11:48
Location: UK

Re: Outdoor sensor and optimal placement

Post by andpotti » 04 Aug 2015, 19:58

or hot sorry

weatherguy112
Posts: 3
Joined: 01 Aug 2015, 03:21

Re: Outdoor sensor and optimal placement

Post by weatherguy112 » 04 Aug 2015, 23:01

Great info guys, thx for sharing. Think I could get used to the look of a radiation shield in my backyard.
Curious if there's a different name for it? Only able to turn up quite a bit pricier options on eBay!

muppet77
Posts: 2
Joined: 18 Jan 2016, 22:01

Re: Outdoor sensor and optimal placement

Post by muppet77 » 18 Jan 2016, 22:11

Hi Andpotti,
what sort of shield did you go for? Was it a second hand Davis one? If not, what model is it and did you know the dimensions before buying.
I would like one but can only find them for £50+

thanks

deeayy
Posts: 22
Joined: 30 Nov 2015, 10:03

Re: Outdoor sensor and optimal placement

Post by deeayy » 20 Jan 2016, 00:03

andpotti wrote:This is my outdoor setup, a simple radiation shield bought second hand from eBay, the sensor fits perfectly inside. checked and calibrated against surrounding airports using their live wx data and 2 local davis systems. I am 100% happy the temp is spot on come rain, shine, or cold.
Does your radiation shield ever get direct sunlight? I'm having a nightmare placing mine because as soon as sun hits it the temperature rises 2-5°C higher than it should be. and at some point during the course of the year, every part of my garden receives direct sunlight.

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