Topic: How accurate is a 5n1

[Beaudog]

Here is a cut from WU station comparison   between my Davis VP2 and my Acurite pro with Bridge.    They are located 1 mile apart.

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[Bushman]

Not a great comparison when the stations are a mile apart.

[DoctorKnow]

A broken clock is right twice a day. Are they always this spot on together?

[nincehelser]

If I recall, the VP2 uses the SHT11 sensor, doesn't it?

The specs aren't that different than the SHT21 used in the 5n1.

[sundevil01010101]

Looks good but as the OP's noted, quite a distance (micro-climate wise ) and it was just one slice in time so a lot more comparison over much longer time needed to assert equal accuracy. 

It also depends a lot on where you live and your station siting too.  I have a Vue/Pro2 w/24hr FARS/Acurite 5-in-1 Pro to compare.

I live in AZ and even on cooler days I see about 5+ too high from my Acurite while my Vue/VP2 are ususally within one degree in spite of one the Pro2 being mounted at 6' and the Vue being at about 26' off the ground.   

The Acurite 5-in-1 Pro is mounted at 16' on top of the same pole my VP2 ISS is attached to and it consistently tracks 5-6 degrees high during the peak direct sunlight hours (back of my house faces SW, so peak sun exposure) even though the aspiration fan seem to be working fine and at full speed.

I do a -5 correction in my Meteobridge but I wish there was a daytime temp correction only option or even better a schedule of correction degrees in 2 or 4 hr blocks as at least for now it makes my nightime temp readings -5 to 6 too low lol.   

I've not been through a full AZ summer with any of the three so once the temps go up all of them will probably be way too high but that's life living in AZ and trying to mount 3 weather stations without pissing off my side neighbors (I gave them both links to WU pages for stations and cams and they are cool) or the dreaded HOA.

[Jáchym]

Hi,
if you use my template, there is a plugin that allows comparing your station data with any metar or other WU site. So if you had both stations (or more) all reporting to WU, you could make all these comparison graphs and statistical analysis (see Station Compare plugin). Or you could even use several "meteotemplates" each using data from different station

[CW2274]

I've not been through a full AZ summer with any of the three so once the temps go up all of them will probably be way too high but that's life living in AZ

My VP2 has been through 8ish summers here, and as long as it's sited properly and well aspirated, the temp will be fine.

[sundevil01010101]

Thanks, good to know.   

Both my sites are a bit of a compromise, one a little too close to a block wall (about 4' ft) and the other on the patio roof (16' ft pole up on patio roof) which I realize is nowhere close to ideal for either but since I have the limited real estate choices and the HOA faactors mentioned I figure the block wall radiation and roof tile radiation at their relative distances will make them both about the same amount high at least .   

[CW2274]

Thanks, good to know.   

Both my sites are a bit of a compromise, one a little too close to a block wall (about 4' ft) and the other on the patio roof (16' ft pole up on patio roof) which I realize is nowhere close to ideal for either but since I have the limited real estate choices and the HOA faactors mentioned I figure the block wall radiation and roof tile radiation at their relative distances will make them both about the same amount high at least .

Hopefully you'll be OK. However, all a fan will do for a poorly sited PWS is show the error, faster.

[Jáchym]

I am in a similar situation.

I live in a 1-room flat. It is actually a house with 3 floors and this "floor" was built later on. The reason I put "floor" in quotation marks is because it does not span the entire area of the house. What I mean by that is that it is connected with the rest of the house via the same stairs and corridor, but only about half of the size of the other floors. The house has a flat asphalt roof and my "flat" is covering about half of that space and the rest is still the roof.

I do not have access to the ground and cannot place my station there, so what I had to do is put the actual station on the roof.... you can probably understand now why I never really cared about the data. The wind sensor is placed above the roof, it is actually at the right height above the ground, but the problem is that I live in a city center and there are much higher buildings around so the wind is much smaller than it should be.

I have the WH1080, a very cheap station, but actually surprisingly accurate. But the problem is obvious. The roof gets very hot on sunny days, so the station temperature is way too high. No shielding would help here because the temperature it measures is in fact correct. I made my own shielding which is better than the original, but it simply gets much warmer on the roof and even if I had Davis with FARS, it would measure the same thing because that is really the temperature on the roof.

But when I now compare my data to the nearby METAR station on the airport, I was very positively surprised how accurate the measurements are. At night for example it is about 2 degrees more - but in this case this is also due to the fact that obviously the city center is warmer and the airport, which is a few km away from the town, has lower temperature. But the difference at night and on overcast days is pretty much constant. Also the pressure almost exactly matches the data from the airport.

But back to the point, in your situation, in my opinion there isnt much point in getting expensive FARS or some sophisticated shielding. If there is no way you can correctly place your station 2m above the ground and in a shadow, then even the most expensive station will not provide 100% accurate data. It will still be usable, but that few decimals difference probably wouldn't be worth the costs.

[sundevil01010101]

One thing I plan to do that may improve everything is I have to get my house painted due to HOA regs (everyone has to after 12 yrs) and my next door neighbor already got his done and one of the things they did is paint ther side of the block walls surrounding the backyard a very light shade.

It looks nice, is approved by HOA so I will get mine done too, it may help the Acurite and the Pro 2 ISS a bit with not absorbing quite so much heat.

At least that's my faint hope..

[Jáchym]

Yes, I guess that would probably help, in my case, the asphalt roof is probably the absolute worst possible surface.

It will then also depend how far from the wall you have it. If it is too close to your house wall then it will be warmed up by the house during winter.

[DoctorKnow]

Update on my readings... Outdoor is on the Roof, a 5 n 1 - Outdoor #7 is in full sun inside an inverted bowl shield I built. OUtdoor #5 is inside deep shade from a water oak that is 50 ft tall. Outdoor #2 is a 3 in 1 in the yard behind me.

Live Data







Sensor

Signal

Metric Data

Imperial Data

Code: [Select]

Outdoor #2 12 sec 29.2°C 46% (dew 16.4°C, heat 29.4°C) 84.6°F 46% (dew 61.5°F, heat 85.0°F) 

Wind #2 12 sec 0.7m/s (avg 0.8m/s) 0° N 1.6mph (avg 1.8mph) 0° N 

Outdoor 34 sec 31.1°C 39% (dew 15.5°C, heat 31.1°C) 88.1°F 39% (dew 59.9°F, heat 88.1°F) 

Outdoor #5 31 sec 26.3°C 41% (dew 12.0°C, heat 26.3°C) 79.3°F 41% (dew 53.6°F, heat 79.3°F) 

Outdoor #7 54 sec 27.2°C 50% (dew 15.9°C, heat 27.6°C) 81.0°F 50% (dew 60.6°F, heat 81.7°F) 

Indoor 36 sec 23.3°C 30% 1017.6hPa (1017.3hPa) 73.9°F 30% 30.05inHg (30.04inHg) 

Wind 16 sec 0.9m/s (avg 0.8m/s) 270° W 2.0mph (avg 1.8mph) 270° W

[DoctorKnow]

Everyone in the Davis topic on sensor chips got me interested again in the aspirated 5 in 1 and making it work in the sun with the solar fan. I enlarged a few holes right under the air sensor and the fan is working really well today. I took the sensor off the hot roof.

Code: [Select]

Outdoor #7 20 sec30.5°C 39% (dew 15.0°C, heat 30.5°C)86.9°F 39% (dew 59.0°F, heat 86.9°F)

Outdoor #2 14 sec33.2°C 35% (dew 15.7°C, heat 33.2°C)91.8°F 35% (dew 60.3°F, heat 91.8°F)



Outdoor #5 47 sec30.2°C 27% (dew 9.1°C, heat 30.2°C)86.4°F 27% (dew 48.4°F, heat 86.4°F)

Outdoor 35 sec29.7°C 38% (dew 13.9°C, heat 29.7°C)85.5°F 38% (dew 57.0°F, heat 85.5°F)

[Inverno]

Though I really like my Acurite, none of them in my area are ever lower in temperature than the Davis or Ambient stations.  On average, the Acurite stations are two degrees higher no matter what. It would be awesome if they could figure out a tweak to the 5 in 1 in order to get down to matchup with the other stations. The Davis and Ambient also line up with the multiple airports in my area, Acurite not so much.

[nincehelser]

I just put up a new 5n1 in Texas.  It's less than a degree F off the airport temp.   

On the other hand, I also measured a 5F difference between one end of the lot and the other. 

Siting matters.

[Inverno]

Sitting does matter but what are the odds that the 8 to 10 Acurite stations are all improperly sited?  I mean, the numbers don't lie.  Davis and Ambient stations must be sited properly too I'm sure.

[DoctorKnow]

My acurite tower in the shield I built runs the same high temp as the 5 in 1 with the fan. Once in a while it will be a degree more if the wind is 0 for long enough. Keep in mind I painted my 5 in 1 on the bottom and enlarged a few of the vent holes. That may be what makes it close to my tower? They both however run a degree or two higher a lot of times than Davis stations near me and usually the same or a degree higher than the nearest Ambient, which is only a few blocks away. Now an Ambient a few miles to my north runs hotter than I do by sometimes 5 degrees F. I believe it is over a deck or something radiating heat. Also I really believe Davis and Ambient use an averaging method to where the sensor does not react instantly to fast changing atmospheric conditions. Acurite reacts very quickly. When it comes to humidity, they are all really close, especially since the nearest Ambient owner apparently fixed his offset on his. It matches good now to everything around.

[nincehelser]

Sitting does matter but what are the odds that the 8 to 10 Acurite stations are all improperly sited?  I mean, the numbers don't lie.  Davis and Ambient stations must be sited properly too I'm sure.

Given that many are purchased at big-box stores and slapped up without much care, I'd say the odds are pretty good.

Do a controlled comparison and I think you'll be surprised.

[CW2274]

Also I really believe Davis and Ambient use an averaging method to where the sensor does not react instantly to fast changing atmospheric conditions.

Davis does not. The sample rate that Davis employs with the SHT31 will snap your neck. The only averaging I'm aware of is done with NWS/FAA sites, no PWS does.

[DoctorKnow]

Also I really believe Davis and Ambient use an averaging method to where the sensor does not react instantly to fast changing atmospheric conditions.

Davis does not. The sample rate that Davis employs with the SHT31 will snap your neck. The only averaging I'm aware of is done with NWS/FAA sites, no PWS does.

OK. I know one of the stations, a VP 2 is mounted on a tower, at least 25 ft high, so that may be why it is a bit low on temp. The other station I have no idea if it is sited properly or not, but the area is low and covered with trees. With poor siting, it is no wonder they run low.

[Inverno]

Given that many are purchased at big-box stores and slapped up without much care, I'd say the odds are pretty good.

Do a controlled comparison and I think you'll be surprised.

I do believe a couple might be wrong but I've driven by some that look to be properly sited.  For instance, there is a 5 in 1 mounted properly about 250 feet from an Ambient station near me, both right on the water.  The Acurite is consistently 2-2.5 degrees higher.  I'm invested in AcuRite so I'll stay, just wish accuracy was more of a priority rather than the new "convenience" items that you mentioned (i.e. ground level battery pack).

[nincehelser]

Given that many are purchased at big-box stores and slapped up without much care, I'd say the odds are pretty good.

Do a controlled comparison and I think you'll be surprised.

I do believe a couple might be wrong but I've driven by some that look to be properly sited.  For instance, there is a 5 in 1 mounted properly about 250 feet from an Ambient station near me, both right on the water.  The Acurite is consistently 2-2.5 degrees higher.  I'm invested in AcuRite so I'll stay, just wish accuracy was more of a priority rather than the new "convenience" items that you mentioned (i.e. ground level battery pack).

Again, I suggest you measure directly at the same point that your station is located.

Randomly trying to compare two stations not yours close together just has too many variables involved.

[DoctorKnow]

Given that many are purchased at big-box stores and slapped up without much care, I'd say the odds are pretty good.

Do a controlled comparison and I think you'll be surprised.

I do believe a couple might be wrong but I've driven by some that look to be properly sited.  For instance, there is a 5 in 1 mounted properly about 250 feet from an Ambient station near me, both right on the water.  The Acurite is consistently 2-2.5 degrees higher.  I'm invested in AcuRite so I'll stay, just wish accuracy was more of a priority rather than the new "convenience" items that you mentioned (i.e. ground level battery pack).

Are you able to use one of the acurite tower style thermo/hygro sensors? IF so, I would go this route if you feel the all in one is not delivering good data. I have done this myself... However, I do not condone putting the sensor in a tree like Acurite, or over walkways etc like Nincehelser. I suggest a proper shield from Ambient weather, Davus; or make one from wood painted white, or some plastic large bowls inverted and painted black inside, white outside.

[Inverno]

I have done that.  The tower sensor always read lower by about 1.5 degrees than the 5 in 1.  My tower sensor didn't have humidity on it and I didn't want to use it's temperature and the 5 in 1 humidity for reasons we talked about before.