Cumulus Support

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.

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

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.

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.

It's permanently 100% here

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

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.

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.

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 ).

TNETWeather wrote: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.

... 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).

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

beteljuice wrote:[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).

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