Topic: Calibration in Cumulus

[Farmtalk]

Hello! As some may have read on here, I've had a problem with my relative humidity being a little too high. Even at 11am, it is registering at 100%, which it certainly should not be after 9 or 9:30am on a sunny day.

I tried messing with the calibration, and set the multiplier to try out at 0.8, only to find out that of course, when the humidity is at 100% when it should be, it calibrates to only 80%.

Would anyone have any suggestions on how to fix this? I know it's an issue because yesterday I had a dew point of 84.... Just a wee-bit too high 

[ocala]

Joseph might it be time to get a new sensor?
Or, maybe check the one you have to see if an ant colony set up shop or maybe it needs some cleaning.
Just a suggestion.

[ValentineWeather]

You can change the slope but if its running 100% when it shouldn't be that's another issue.
Some examples:

I've adjusted my slope like this -5 on humidity, multiplier 1.054. The way I came up with 1.054 is after (-)5 = 95 x 1.054 =100%. So you still reach 100% but knock off 2-3% as humidity drops.
Another example humidity 60%-5=55 x 1.054=57%, so you have adjusted humidity down 3%.

This won't take care of a major sensor error however. In that case replace sensor. 

The multiplier can be changed even more which effects low end drastically. -20 humidity, multiplier 1.25. So 80 x 1.25=100% still. In this slope your lower humidity range will see the most effect. Example 40%-20=20 x 1.25=25%

[ValentineWeather]

One more thing if you change this in Cumulus make sure you check mark "calculate dew point" under station settings.

[Farmtalk]

Thanks for the tips everybody! In due time, I may look into getting another sensor, but I'll try this out first and post my results 

[Farmtalk]

Thanks for the big tip Val, I went ahead and put the add/subtract at -15 and the multiplier at 1.176 since my difference has been a little on the larger side. I'll let everybody know how that goes tomorrow! 

[ValentineWeather]

Yeah, see how it does. You can always change the multiplier if needed. I worry when you said it was  on 100% so long it may of failed.

[Farmtalk]

Yeah, that's where it'll be interesting to see how it does. It's been showing 100% until around 10:30 or 11:00 (Check my graphs, but today's is screwy due to a power outage). We'll see what happens for tomorrow, but it's worth a shot. I'll buy a new sensor if needed.

[Farmtalk]

Well, unfortunately it looks like the sensor's the issue, as despite the calibration change, I didn't drop below 100% humidity until 11am despite plenty of sun. I changed the batteries last November, and we did have one day here where it got down to -20F and windchills between -30F and -40F, so perhaps they got sapped. I'll try that and if not, it's looking like a new sensor    I can't complain though, it's been a good station. 

[CW2274]

Not saying this is particularly your case, but if more people that post their data on-line would regularly replace their sensors as preventative maintenance, (never gonna happen) we'd obviously have better overall stats to compare. Enthusiast pipe dream.

[Farmtalk]

I've just gotten into the hobby of really beginning to store data at my place. There are no stations within 30 miles of me, so I thought it was time to give it a shot.

But I aim to make sure that my data is correct 

[CW2274]

I've just gotten into the hobby of really beginning to store data at my place. There are no stations within 30 miles of me, so I thought it was time to give it a shot.

But I aim to make sure that my data is correct