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

[Jose1701]

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 –30°C up to +70°C. This area does mean from 0% up to 100% global radiation. To avoid some calculations you are able to set this by an offset in Weather Display. The resistor works as an adjustment resistor. In case of the THGR 810 we're speaking of an analog device. Therefore the modification is kind of simple and varies from type to type only regarding to the resistors you have to use. You can get the solution by using an ohmmeter. In case of digital measurement it is different. These won't be modifiable by using this method. I do not have any details about which units are analogue and which are digital. If you have information about that please leave me a message. I will then update this manual. But now to something completely different *lol* the modification of the unit. First you have to open it by removing four little screws at the reverse. You will see at the right place of the picture the temperature bead. Pic 1 (red X). This has to be replaced with the resistor by the light probe in a row. Alternatively you can cut off the RJ12-jack and solder it as you can see in pic 2 or you can make a professional jack to connect the light probe. This also depends which light probe you are using.

pic1

Now you have to solder the wire from the light probe to the board were once the temperature bead was. The other wire you connect with the resistor which you have to solder with the other connection on the board.

pic2

So long to the modification of the sensor. This has to be configured in the software. You first need to open Control panel --> Solar/Lunar Coordinates and put in your coordinates. This is important to let Weather Display calculate sun rising and sunset.

pic3

Secondly go to Control panel --> Solar Sensor. Now you need to configure the following settings:

1. In Solar Sensor in Jar Setup you have to tick that you use a temp and that this one is overwriting the measurements of a possibly existing UV sensor.

pic4

2. In Max Solar Time of Day/Time Zone/Lat/Long, Fudge offset put in the right coordinates and tick as you see in the screenshot. The tick mark at the bottom "Time of day shadow offset" regards to a possibly amount of shadow during the day so you can raise the radiation manually.

pic5

3. In Graph Plot/Misc Settings you have to tick how the curve may appear on your screen.

pic6

4. The following area (Threshold/...) conduces to calculate at what "time" the conditions have to show whether its sunny or not. Here you need to experiment a bit to get the right settings regarding to your location. Perhaps you have to modify this later or during the year.

pic7

After these modifications (settings) the sensor has to work and show you something like that, e.g.:

pic8

pic9

Good luck!

 

This manual came into being by seeing this website: http://www.pc-wetterstation.de/wetter/solarsensor.html

I wish to thank Alexander Horlamus who operate this site: http://www.horlamus.info/

Also thanks to Chuck Goble for helping me out with the English translation. http://www.chucksweather.com/

Author: Florian Bruhn www.wetternet.org

contact:  

[Windy Greg]

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

[NorCal Dan]

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

[rickym]

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

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?
• 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

[Jose1701]

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

[niko]

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.

[rickym]

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

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

[Jose1701]

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

[Geoff P]

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 £5.40 apart from that I have used the same circuitry as above.

Will keep you informed of final results, looks better than having a temp/humid sensor in a jar.

Geoff

[PinkyCZ]

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://www.weather-watch.com/smf/index.php/topic,48145.msg393940.html#msg393940) 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 


my 2c 

[niko]

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

[PinkyCZ]

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 

[niko]

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.

[NorCal Dan]

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.

[PinkyCZ]

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  . 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!