Use an OS THGR 810 temperature/humidity sensor as a global radiation sensor

How to modify a Oregon Scientific THGR 810 temperature/humidity sensor to a global radiation sensor.

You need:

  • THGR 810
  • Light probe
  • Resistor 2,5kOhm (in the pic there are two resistors 2,4kOhm + 100 Ohm)
  • Screwdriver
  • Electric soldering iron
  • Software e.g.: Weather Display

The temp-sensor is measuring from

Hi
I am in New Zealand and have been looking around for a “light probe” but cannot find one. Is this the same beast as a “Photo Diode” ??. If so there seems to quite a few different ones available. It seems from your description the light probe produces voltage in which case I guess the photo diode would suffice but the ones I have seen have just bare wires rather than a lead so are difficult to set up re weathering.
Any further info would be good as I am not an electronics type person, more a broken down builder bloke.

Cheers

Some pictures of the one I built in the thread here.

G’day Jose,

Thanks for your detailed explanation here. It’s most appreciated. I’m about to set up my WMR 200 system following your instructions, but depending on your answers to my questions below, please:

  • What actual parameters does this system measure – just solar radiation or UV as well?
  • Will it enable me to discard my current UV sensor (UVN800). It seems to be a heap of garbage anyway
  • Is it like a thermometer in a jar and will it measure (or indicate) cloud cover?
    [li]If it measures cloud cover, will it do so at night as well as day?
  • When set up, do I place it in a Stephenson’s Screen alongside my existing temperature/humidity sensor or somewhere else?

Cheers,

Rick

Very busy regarding to personal and business problems. I try to give some answers:

What actual parameters does this system measure -- just solar radiation or UV as well?

Only solar radiation

Will it enable me to discard my current UV sensor (UVN800). It seems to be a heap of garbage anyway

No, therefore it measures only solar radiation you need your UVN.

Is it like a thermometer in a jar and will it measure (or indicate) cloud cover?

No it won’t directly. Have a look at pic7

When set up, do I place it in a Stephenson's Screen alongside my existing temperature/humidity sensor or somewhere else?

I don’t understand what you mean. Sorry, not a native speaker.

Regards

Jose

When set up, do I place it in a Stephenson's Screen alongside my existing temperature/humidity sensor or somewhere else?

It measures solar radiation so the sensor part needs to be in full sun, not shaded.

Thanks for getting back to me Jose. Most appreciated. I think between you and Nikko all questions are answered anyway – the sensor needs to be in the sun and not inside a box, eh? Do you have any photos of what it looks like when set up and showing the location of the solar sensor?

Thanks again,

Rick

Well, I will try to make some photos the next days, but as I said, I’m very busy at the moment.

Regards

Jose

Hi All,

I have just done this conversion and all though it is still on test things are looking good, I have used a sensor which I purchased from RS Ltd at a cost of

Have done this already and yes it “works”, but there is a big questionmark about what you are really measuring by this.

The photodiodes used by different people have different characteristics and responsiveness to wavelength so the different users data can actually be hardly compared.
I pointed in another thread (actually hijacked my own thread a bit by the subjetc, but see here http://discourse.weather-watch.com/p/379374) that the biggest problem is that temperature sensor that you are removing is nonlinear and the unit is compensation for this. Replacing it by photodiode with nearly perfectly linear responsiveness gives you very biased readings. As a result, your unit is very sensitive at low light conditions , but at full day it is very little difference between 1000 and 800 W/m2. WD can only interpret the figures you feed from the unit so the temperature is converted solar values that are far from what they should be.

After little tweaking you can use it reasonably well to tell your current cloud cover level, but remember the solar values obtained by this are purely fictious.

I did this mod and decided not to use. Whatever I store should be more or less accurate, it is impossible to have a good data from such mod IMHO.

It is far better to go ahead with temp in jar solution, your readings will be more close to what they should be. Plus - you don’t need any photocell :wink:

my 2c :roll:

Pinky, are you still using photodiodes instead of the recommended cds photocells?

Yep, building up a unit using BPW34 that has a linear relation between W/m2 and current + opamp + … feed the values to WD somehow, probably 1-wire.

What you mean by photocell? Photoresistor??
I decided not to even try photoresistors, (despite I have some spare from the past) as it is non linear (would not be a big problem since the original thermistor is also nonlinear, but most likely “differently”) but mostly as it is very dependent on the ambient temperature except of the light conditions. This would be a problem I gues as different readings would come out under the same irradiation depending on the ambient temp (summer/winter)… having the sensor in some kind of container to protect from outside would also contribute to further heating I’m afraid :frowning:

All I can say is that users who have built this using cds photocells (photoresistive) have gotten an acceptable result. But I do agree that PIN + OpAmp + Optical diffuser is definitely the way to go for an accurate result.

Keep in mind that most of us do this as a hobby. We spend a couple hundred dollars on some equipment, stick the thing out in the yard, and enjoy tracking the data and making it available to the public. What we don’t do is have expectations of our data being accurate to the 10th decimal point.

I agree Niko, the photoresistor response will be similar curve to thermistor so it should be easier to tweak. I’ve done the mod using BPW21 photodiode and it experienced all the related problems - mostly the readings are impossible to match to reliable W/m2 readings, even the cloud conditions are diffiult to tweak… but it can be working once a man get it setup and at least can serve to have sunhours counted.

NorCal Dan, your thread has been a great inspiration when I have started this! I’m sorry if my above message sounded like there is only one solution, it isn’t. I’m not a native speaking :oops:. I’ve seen several mods around and actually liked the idea of having a vireless unit converted to a good solar sensor, but after all the work done, I’m not satisfied with the sensitivity so I’m still working on final design that will not be wireless (for thet the WD built in temp in jar is the best solution IMHO). I just wanted to share the info and experience I’ve gathered and why I decided not to even try photoresistors - in my area it is around 55 degrees difference between summer (+extra heat because of the unit being housed in a box) and winter and photoresistor is rather temperature dependent too. I think I could no way get a reliable irradinace values going this way.

Will post the result and final design details once I’m satisfied with the readings!

Hi,

which photo diode type,number is used by these avtor Jose1701? Is these type of modification of the sensor better then original Oregon UVN800 sensor?

The original sensor UVN is only for UV-Radiation. The one modified by me is for global radiation.

I’m using a lightprobe like this one: http://www.conrad.de/ce/de/product/156518/Lichtfuehler-50-2000-Lux-Hygrosens-Lichtfuehler-wetterbestaendig-Lichtfuehler-wetterbestaendig

Regards

Hi,

today my sensor is working. I have on question. When is 33