Humidity - Is 100% theoretically possible?

[Repairman77]

Just wondering if 100% Humidity is theoretically possible.
I have been trying to calibrate the humidity sensor via C1 and in rain it normally reads 99%.
However on a misty day like today it's reading 100%. If 100% is not possible is it best to back it off to 99%?
I know it's splitting hairs but it's just been puzzling me.
Mike.

[beteljuice]

You are very lucky if your sensor reports that high (or maybe not !) - NONE of the electronic hygrometers are beter than +/- 4% above 94ish, and the drop-off is not linear and cannot easily be compensated for. If you discover your lower range is high (by that I mean at about 25 => 30 % reading) drop it a point or two.

You may have noticed that Cumulus has a tick box for "Make 98% => 100%", as well as the offset and multiplier, because of this dodgy top-end which most never reach.

In a similar fashion, depending on the manufacturer of the hrgro chip, below 15% is meaningless and some systems simply don't report it !

So I'm afraid all those people who use the php coded Fire Warning / Chandlers Index advisory are never going to see the real danger advisories as they kick-in below what their sensors can give out

[Repairman77]

Thanks for your input Beteljiuce,

I have the Humidity set to +10 as the sensor never gets that high.

I guess these sensors are like all the others; hardly the most accurate thing on Earth.

I've left it set at 100% but just wondered if humidity ever actually gets that high?

Mike.

[beteljuice]

Yes - in real life humidity will / can get that high.

+10 offset does seem rather high !

For my La Crosse unit I use a mixture of "Make 98 = 100" and a small multiplier (1.03) - still to be tweaked. As a trade off between 'normal' and high RH.

[steve]

It's permanently 100% here

I exaggerate somewhat; but it's quite often 100%.

[TNETWeather]

100%?

That would be hard for a lizard like me to deal with.

We many times go in the teens for humidity, I've seen it as low as 4%

Right now (after rain yesterday) it is 55% @ 62°F In a day or so it will drop down to 20% or so unless we get more rain.

Rain is somewhat of a relative term here as well... Rain yesterday was a whopping 0.01in ... many places would not even consider that measurable rain.

[Repairman77]

Thanks for all your comments.

It does need to be offset +10 to get to 99% or 100% and that was set in a rain downpour.

I haven't got a multiplier or the 90%-100% setting on my Cumulus1 program; not where that lies?

I know humidity is a very hard thing to measure accurately. A friend of mine, who like me is a calibration freak, LOL, bought a pro sensor a couple of years ago, which you use in conjunction with a digital multimeter, but that was only +-2% and it cost £85.00.
So the chances of these WX station sensors being anywhere near that accuracy is unlikely.

Mike.

[akasonny]

Rain? You got rain? How might we get some of that?

Humidity here is regularly less than 10% in the summer ... I think the Fine Offset doesn't accurately measure below 10% so I have to rely on the Nat'l Weather Service for that info. I think we're actually drier than Phx/Tempe, Kevin. You guys have more irrigation up thataway (and more golf courses ).

100%?

That would be hard for a lizard like me to deal with.

We many times go in the teens for humidity, I've seen it as low as 4%

Right now (after rain yesterday) it is 55% @ 62°F In a day or so it will drop down to 20% or so unless we get more rain.

Rain is somewhat of a relative term here as well... Rain yesterday was a whopping 0.01in ... many places would not even consider that measurable rain.

[beteljuice]

... I haven't got a multiplier or the 90%-100% setting on my Cumulus1 program; not where that lies? ...

"Use 100% for 98% Humidity" tick box is located:
Configuration => Station Settings => settings sub-panel

Humidity multiplier is in the same place as the offset:
Configuration => Calibration => Multipliers sub-panel

Re. sensitivity - they haven't got any - Just because it was raining doen't mean it thought it was wet These things take a surprisingly long time to catch up with change, and even longer to reach the final steady bit (if ever in real life).

[akasonny]

Yes that's me. I admit it. It all started when I was a wee boy....

[Re. sensitivity - they haven't got any - Just because it was raining doen't mean it thought it was wet These things take a surprisingly long time to catch up with change, and even longer to reach the final steady bit (if ever in real life).

[harrym1byt]

One way to resolve it, would be to use a software look up table - assuming the RH sensor doesn't vary with temperature.