Temperature readings

[water01]

I put my Maplin WH1080 up about 2 months ago, and with this great fine weather spell we have been having it has become increasingly obvious that I have a problem with my temperature readings during the day.

I think it is because we have a fairly small garden and during the day the sun shines down at the back of the house reflecting off the house at the temperature sensor and increasing the temperature reading by approximately 5C.

Readings at other times of the day and especially the night are perfectly correct, so spike removal will not work as it is not time of day dependant. Any suggestions on what I can do to make it produce more valid readings at the middle of the day, otherwise I going to end up with British record readings .

[mcrossley]

I think there are only two options really, relocate the sensor, or provide some additional shielding?

If the sensor is near a wall that gets heated in the sun, then it is going to suffer from re-radiated heat. Putting a board between the sensor and wall to block the IR from the wall from hitting it will help, but depending on how close it is, it may still suffer from the surround air being heated by the wall.

Any more for any more?

[freddie]

Definitely needs to be away from solid structures like walls. Better to have it in shrubbery at the other end of the garden than near a wall.
To help when the wind is light, you could also rig up a small fan to keep the air moving past your temperature sensor.

[water01]

Mmmm that's what I thought was going to be said. I think blocking the radiation from the back wall of the house is going to be difficult as I would also be blocking the signal from the transmitter.

Moving it further away from the house is an option but I think I will need a longer pole, and lockdown doesn't give me many options to do that .

Nearest site to me at Weston-Super-Mare is currently 25C and I am at 29.6C so I will have a play and see what I can do.

[mcrossley]

The board could be a piece of plywood, preferably marine ply, paint it to blend in - that should be fairly transparent to radio signals. Its doesn't have to be thick to block IR.

[sfws]

I put my Maplin WH1080 up about 2 months ago, and with this great fine weather spell we have been having it has become increasingly obvious that I have a problem with my temperature readings during the day.

David

I have a similar problem, when (after my own move) I put up my Chas Olson weather station in mid-January I mounted it on the gable of a garage, good line of electromagnetic radiation to the console in the house, but it is now close to the garage wall that radiates heat and still directly impacted by the evening sun now it sets in NW. When I first installed it, I put it above the roof, and there it was was obviously reading high due to sun all day (we did have some sunny days in late January), so I tucked it below the roof where it became close to the brickwork and was shaded from the winter sun.

Recently, I ordered some white plastic louvre vents (Screwfix is still open in UK and sells these for next day delivery, but because my local ParcelForce is so busy, there has been a delay in them getting the goods to me).

I have a few pieces of uPVC left over from window replacements. Wickes in UK is able to supply various uPVC parts, but you may have to wait a while!

I will be assembling all these to construct effectively a simple single layer Stevenson screen that will maintain air flow, but block most sun rays and break up the radiated heat from the wall.

it may still suffer from the surround air being heated by the wall.

My screening won't be perfect, but it will help. When the dominant south-westerly blows, it will move air parallel to the wall, so that might help too. Anyway, with the new screening in place I will be able to move my sensor out from the wall compared to where it has been close to the wall for minimal sun ray influence.

Assuming I get it assembled this evening, I will be up the ladder tomorrow to check it can be fitted okay, and will then try to see how it works. Another forum member currently (his planned move south has been delayed by current lockdown) has a site several km from mine, and I compare my temperatures with his to get an idea of how far out mine has been, hopefully after I have made this change I will be closer to his highs.

[water01]

That sounds interesting. Do you have a basic design I could follow? I am fairly handy with tools, so just an outline drawing would do.

[sfws]

I'll take a photo or two in the morning, and I might get a drawing done by then too.

Basically, I bought 3 x 4695D in Screwfix catalogue https://www.screwfix.com/p/map-vent-fix ... 52mm/4695d, they are 9" x 6" so match the tall narrow Fine Offset transmitter reasonably well. The louvres are vertical, but I slant them away from the sun direction. The back and top are solid uPVC https://www.wickes.co.uk/Wickes-PVCu-So ... m/p/187421 and I have used square section uPVC https://www.wickes.co.uk/Wickes-PVCu-Wh ... m/p/162639 to do the joints, as I can use wood screws to attach the vents to those pieces. The Wickes URLs are the closest match to the pieces I had that were left overs from work done by a contractor.

The bit I have not yet worked out is how to fasten this open bottom cuboid to the arm that holds the transmitter. At the house I owned previously, I had my weather station attached to a fence, and I fastened my previous cage to that fence, but it was broken in the removals, and anyway the mounting will have to be different this time. I will probably find some way of screwing onto the arm, and fit some sort of spacer.

EDIT: Corrected grammar error not picked up by spelling checker (as I used wrong word)!

[sfws]

David,
Not done any drawing, I have been busy with many other jobs!
Here are some photos, taken just now, before I climbed the ladder, and after I safely installed my creation. You will see I did not need to use the spacer I had added in earlier photos in final install. I simply screwed up through Fine Offset arm into my creation.

[water01]

Great thank you, I might give that a go.

Bit late now but take care on the ladder!!

[sfws]

I have a spreadsheet that records my maximum and minimum temperatures each day in April. Alongside I have the same measurements from someone else using Cumulus as close as I can find. The spreadsheet shows the difference in each pair of readings. It is all very perplexing (

my spreadsheet comparison for whole of April so far is perplexing

) there does not seem to any consistency in the discrepancies. But most significantly, the discrepancies seem to have got bigger since I added my shading cage.

The way microclimates vary greatly in this county, I was not expecting a good match. Also the evening sun is still distorting my maximum temperatures to much later in the day, yet that was exactly the opposite outcome to what I wanted, and why I bothered with climbing up ladder to make modification?
I will continue to update my spreadsheet for a few more days before I share it.

I did have a look at Mark's site on his today/yesterday page, but that is full of strange figures like different max and min temperatures but both showing as midnight, even the data from met office is strange - highest rainfall is -1.0mm in Leek!

If the sensor is near a wall that gets heated in the sun, then it is going to suffer from re-radiated heat. Putting a board between the sensor and wall to block the IR from the wall from hitting it will help, but depending on how close it is, it may still suffer from the surround air being heated by the wall.

Perhaps Mark is right, I am still too close to the wall, maybe I will climb ladder again, and attempt to find a way to reposition it again.

I've changed my roof setup so that it is all on a single 2" pole. Transmitter clamped to the bottom, anemo & solar to top. The cables run down the inside of the pole. I now have two sliding clamps on the P-K brackets. Which means I now just have to get up as far as the brackets, release those and the pole slides down. When I'm done, slide it back up again, clamp it off and it retains its vertical alignment.

In this other topic it is mentioned that Mark has his station attached to a gable, but presumably his temperature sensor is above roof level to avoid these wall effects?

Where I lived before I was in visual sight of a TV transmitter, and I had the connecting wires inside the pole to stop them acting as an aerial, here my wires are on outside of the pole (it is one sold for TV aerials) and it is clamped to the gable with a standard TV aerial clamp, but my transmitter is just above clamp currently, not above roof level.

[freddie]

The way microclimates vary greatly in this county, I was not expecting a good match.

Knowing the geography of your local area, I would suggest that you should see a better-than-average match.

Also the evening sun is still distorting my maximum temperatures to much later in the day, yet that was exactly the opposite outcome to what I wanted

Sounds like your temperature sensor is (too) near a west- or southwest-facing wall.

I did have a look at Mark's site on his today/yesterday page, but that is full of strange figures like different max and min temperatures but both showing as midnight, even the data from met office is strange - highest rainfall is -1.0mm in Leek!

I took a look at what Leek has recorded. It was reporting a "trace" of rainfall - which can be summarised as rain that has fallen (or been detected) at the site but measuring less than 0.1 mm. The data feed Mark is using must use a special marker for a trace of rain, and Mark's page has translated that to -1. Perhaps -1 is used to indicate a trace of rain, as you can't have -1 mm of rain, so looks like a good marker to use.

[mcrossley]

In this other topic it is mentioned that Mark has his station attached to a gable, but presumably his temperature sensor is above roof level to avoid these wall effects?

I have two transmitters, one up on the gable for wind & solar. The second is in the back garden away from the house for temp/hum and rain.

[sfws]

The second is in the back garden away from the house for temp/hum and rain

Noted.

[sfws]

I have a spreadsheet that records my maximum and minimum temperatures each day in April. Alongside I have the same measurements from someone else using Cumulus as close as I can find. The spreadsheet shows the difference in each pair of readings

After I wrote that post, with helpful advice from the person whose readings I am comparing with, I moved my sensor within its cage away from the wall. 6 days later I am definitely seeing the benefit. (I have stopped the spreadsheet at this time because I now have an electrician back to finish off the rewiring he started before Christmas, consequently my router and PC will remain off during each day and I won't be recording nor posting!)

I attach a rushed photo of the new arrangement and the spreadsheet. I believe the alterations (putting cage round sensor and moving its position) can be judged a success. I know there is still signs that the sunshine is affecting my maximums as the discrepancy is higher on sunnier days, but life is not perfect. I just am pleased that my various trips up a 3-part ladder to reach 6 metres above ground level have resulted in such success. Each time I spend much more time carrying the ladder, extending it and particularly in making sure the ladder is safe, than I spend up it!

You might be surprised by the discrepancy between his and my minimums, but I expected to see a discrepancy of about one degree as in the winter months he was seeing frost on more nights than I was (I also compared our temperatures during January and February, as at that time I was adjusting my Cumulative Chill Hours figure and checking the daily figure). Also, his back garden site surrounded by the rest of his village might be more of a frost hollow than my more open near the village edge location. Also his sensor is at the right distance of 1.5 m agl from the ground for official measurements while mine now is about 6 m agl and there is a small variation in temperature with exposure and height.