Emily's Weather Blog

Sensor test results table

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As promised at the end of last month, an evaluation of the sensor values under differing light conditions.

Time 0hms Cloud cover (8ths) Description Observer
12/06/11 04:45AM 3300 1 pre sunrise Clouds on eastern horizon, lit by sunlight – sun behind hills chrisw
05:00AM 2000 1 Sunrise – sun just behind trees chrisw
05:07AM 1750 1 Sunrise – cirrus band and blue sky overhead chrisw
05:10AM 2000 1 Same conditions but in shadow area to get down scatter reading chrisw
05:15AM 1050 1 blue sky cirrus clouds overhead sun about 3 degrees above horizon emily
05:30AM 800 1 same conditions but sun about 1-2 degrees higher emily
05:45AM 700 2 cirrus clouds and blue sky sun at 5 degrees bank of cloud coming in from south not yet affecting readings emily
06:00AM 450 3 cirrus cloud still above sun at about 7 degrees bank of cloud from south moving further north emily
06:15AM 375 5 cirrus cloud and blue sky still above sun at about 10 degrees bank of cloud from south almost over head though emily
06:25AM 435 7 sun slightly covered by thin bank of cirrus cloud and cloud from south over head now beginning to affect readings emily
06:40AM 700 8 only last snipits of blue sky sun covered by clouds from south (now covering most of the sky), sun at 13 degrees emily
06:55AM 635 8 sun covered by thick cloud at about 17 degrees emily
07:15AM 800 8 sun now not visible behind cloud emily
07:50AM 700 8 sun now not visible behind cloud raining at the moment (light to medium rain) emily
08:30AM 700 8 still raining and still no visible sun emily
09:00AM 650 8 clouds slightly lighter white still raining and wind picking up emily
09:30AM 700 8 full sky of thick cloud no visible sun, medium rain and wind picking up emily
10:00AM 550 8 full sky of thick cloud still no visible sun wind dying down rain picking up emily
10:30AM 430 8 cloud directly above head whitening slightly, rain still getting heavier. emily
11:00AM 500 8 cloud not any whiter, rain dying down emily
11:30AM 480 8 cloud not any whiter, rain the same emily
12:00PM 550 8 Same conditions as before emily
12:30PM 530 8 Same cloud yet raining heavily emily
01:45PM 545 8 clouds slightly lighter white still raining emily
02:30PM 590 8 Same cloud yet raining getting lighter emily
03:00PM 530 8 raining heavily clouds still full covering sky emily
04:00PM 680 8 Overcast chrisw
06:00PM 650 8 still overcast emily
07:00PM 750 8 still overcast emily
07:30PM 670 8 still overcast but clouds lightening in colour emily
08:00PM 900 8 odd snipits of blue sky overhead but low cloud/ fog coming in from south emily
08:40PM 1600 8 blue sky gone low cloud from south still moving in emily
08:55PM 3330 8 dark low lying clouds, drizzle emily
09:05PM 3700 8 Still dark low lying clouds, drizzle emily
09:15PM 3800 8 same as above emily
09:20PM 6500 8 same as above emily
09:29PM 7400 8 Supposed sun set however unknown because sun covered by thick cloud, still drizzle emily
09:35PM 10000 8 beginning to darken slightly. emily
09:50PM 25500 8 slightly darker but still drizzling emily
10:00PM 72000 8 getting darker almost black sky yet still able to see drizzle stopped emily
10:08PM 160000 8 dusk chrisw
10:20PM 600000 8 dusk chrisw
10:35PM 2350000 8 dark emily
13/06/11 10:20AM 240 5 broken cloud – in sunshine chrisw
11:00AM 290 6 sun behind thin white cloud chrisw
12:40PM 250 4 broken white cloud – sun unobstructed chrisw
07:05PM 298 3 cirrus partially obscuring sun chrisw
09:55PM 12400 2 10 mins after sunset chrisw
14/06/11 01:00AM 24000000 2 moonlight ¾ moon chrisw

So, in conclusion the simple photo-resistor (LDR) sensors chosen give a range of values ranging from a few hundred Ohms in bright sunlight, to over 20M Ohms under moonlight.

This is obviously too wide a range of values to cover with a single scale (there are only 1023 steps on the ADC input on the micro-controller board I will be using) – so tests and some graphing will follow to chose what ranges to cover

I have located a conversion table for EV (exposure value) to Lux for our photographic light meter, so will retest some of the above typical values in conjunction with the Lux reading to give some more measurable values to the table

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