Cloud Sensor Project

[Mike]

Does anyone know how I can cheaply rig up the following :-

2 x Temperature Sensors to be interfaced to a PC to enable monitoring and monitoring of temperatures from the two sensors? I am looking at a solution for less than £100 (and preferably around £50) if possible. The two sensors would not need to be particularly accurate but should both read the same temperature in the same location (+/- 0.1°)

[Mac]

not too sure if you will find that accuracy in the price range,

Do you need real time constant monitoring or just data logging?

these might help

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5363283

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4901064


this ones a bit expensive, but its 0.1C

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2890473

mac.

[Mac]

Just found this one as well,

http://www.rapidonline.com/Tools-Fasteners-Production-Equipment/Test-Equipment/Data-Logging/USB-Real-time-data-logger-temperature-humidity-and-dew-point/82317/kw/

[Ian]

you  can't post questions like that and not say what it's for. It's forum posting rule number 27a subsection 2 clause 4...

[RobertM]

Mike, have a look at http://www.active-robots.com/products/phidgets/sensors-phidgets.shtml for diy, not sure what the resolution is though.

[Mike]

Mac it has to have real time monitoring (well as long as I can have updates from it every minute) and Ian it is for an idea I have for a cloud sensor. No idea ifd it would work, it would just be an experiment.

Robert thanks for that link. That appears to be the cheapest I have seen so far. They have lots of other nice stuff on that website too.

[doug]

     Mike... I realise that this is no use to you for your query, but did you get the e-mail I sent you about the cloud meter on the Fitzroy Barometer??  Check the link..if it worked.. about the barometer and you will see what I meant.  Hope you manage to construct the gizmo.

[Mike]

Thanks for the info. guys.

I have found an even cheaper option - http://www.arduino.cc/
- About £25 attached to two of something like this - http://www.national.com/mpf/LM/LM35.html - about £5 each.

Doug - Yes I did thanks. Very interesting.

[RobertM]

Sounds like a really good idea Mike.  I take it you're measuring the difference in radiant heat energy (temperature) between sky and ground ?  I expect you could use a peltier but I would imagine the generated current would be impossibly small to measure !

Had a hunt and thought this might help, it uses the National Semiconductors LM75 ... http://www.raphnet.net/electronique/usbtenki/index_en.php

[Mike]

Thanks for that Robert. The sensor is based on two thermometers, once measuring ambient and another doing the same, but placed inside a blacked out object (e.g. jar or tin painted black) to act as a 'black body' (i.e. one that would get colder at night due to radiation into space).

So, in theory, you can measure the difference between the two and if ambient and black body are approx. the same temp then it is cloudy. If the black body reading is colder by about a degree then it should be a clear night and anything in between partly cloudy.

It's all based on this thread I came across on Weather Watch...  http://www.weather-watch.com/smf/index.php/topic,34244.0.html

[MarkS]

Great idea!  I reckon they should both be in jam jars but one black and the other white.

It reminds of a conversation I once had with a friend:

Me:  In theory, central heating radiators should all be painted black, not white, because it makes them more efficient.

Friend:  Really?  How does the radiator know it has been painted black?

Me: [Too stunned to reply]

[RobertM]

Makes a lot of sense but if you put your sensors in jam jars then they will have a relatively high thermal mass.  It really depends on how responsive you want it to be to changes in cloud cover or not as the case may be.

[Mike]

On that forum there seemed to be two successful devices, one was a very small baby food jar so that a) there is no air flow over the sensor and b) there is a small amount of air inside the jar to heat up or cool down. The jar would need to be hermetically sealed. Another device was simply a piece of polystyrene with a hole cut in it to haf the depth of the block, the inside of the hole painted black and the sensor put inside, with a piece of clingfilm wrapped around it all to make it waterproof.

I like the sound of the second device personally. I am thinking maybe two pieces of PVC pipe, both with a polystyrene plug in the bottom and a piece of glass/perspex at the top. Sealed at either end. Sensors inside both but with one painted black inside the tube and both pointing at the sky.

[Mac]

Just found this, £99.

http://www.picotech.com/thermistor.html
resolution 0.003C
readout every second.

Interesting reading about the theory.

[Mike]

Yeah but that's £135.00 compared to about £30 for the Arduino plus bits !!

Plus with the Arduino and the Phidget you get full access to the raw data so can write your own programs to read data and do other stuff. I like the fact there are multiple digital/analog inputs so I could also couple it up with a light meter and maybe a wind speed indicator or something like that, to establish ideal observing/imaging conditions and then set off some kind of alarm.

Plus, the Arduino is dead cheap and also has a little CPU on board meaning you can upload programs to it and make it do things independant of the PC. There is even a bluetooth and radio version so you could make a completely wireless device if you wanted to.