StdCalibrate/corrections for radiation reading

[colin....@gmail.com]

Hi all

I have a situation whereby (I think) I have some odd building reflections spiking my solar radiation sensor. This results in occasional readings way above the expected maxSolarRad value.

I'm going to try and sort out exactly what's happening but in the meantime I wondered if it would be possible to use StdCalibrate to correct those errant readings?

Putting it simplistically what I'm aiming for is a statement along the lines of;

radiation = maxSolarRad if radiation > maxSolarRad

I'm not sure if that syntax is correct above or will even work,  but this will hopefully remove any spikes greater than the expected maxSolarRad?

Am I barking up completely the wrong tree?

Many thanks

Colin

[Greg Troxel]

Yes. You have data and you should record it.

There are three situations, at least, where you will measure a radiation
that is higher than maxSolarRad.

- small amounts, because the formula is approximate

- reflections from mirror-ish surfaces resulting in direct plus extra

- lensing from cloud edges, where you see = in clear sky, lower in
cloud, and a messy pattern as the edge happens

In these cases, you really can get measurements that are valid and above
maxSolarRad.

The question is: what are you trying to do and what do you think it
means?

If you are trying to find some value that represents the highest value
you saw more than momementarily, compute the 98th percentile of
radiation, or 95th or 99th. Then the data means what it says.

As soon as you extract data with a conditional on theory, you have
something that is very hard to reason about and describe. My advice is
don't go there.

This is different from rejecting values of 120% humidity reveived from a
sensor as obviously bit errors. Seeing too-high radiation happens
without corruption.


I just record it, and graph it, and I don't worry that it's sometimes
higher than theory. Real data is like that.

[Colin Larsen]

Hi Greg

Many thanks for your reply, you raise some very valid points about data in the real world. Maybe I'll just leave it as it is :)

Cheers

Colin

[Dale]

Just chiming in:  I have had some luck over the years calibrating my
solar sensor and having it track pretty close to the curve generated to
predict what the maximum should be.


Then I noticed that while most of the time it is within a tiny bit of
the displayed readings and the predicted curve, sometimes it goes nuts
and exceeds the value by a 5% or so.

It never happens on a clear day.  It often happens when clouds are
passing over.  It never happens when truly cloudy.

I have received the same advice and conclude it is NOT any gremlin nor a
reflection (which I thought of as an initial possibility) but due to the
cloud edge effect.

Now I just take it as part of the function, and on perfectly sunny
cloudless days enjoy the sensor output tracking predicted values.

Dale

[Colin Larsen]

Thanks Dale - appreciate your thoughts and agree with you. It's always great to have your thought process tested occasionally :)

Colin 

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