Topic: Humidity Difference?

[blizzardof78]

I just recently purchased an analog temperature / humidity combo. I placed it outside in a radiation shield facing the north this afternoon. I noticed a difference between the humidity on my Davis Vantage Vue and the Nova Lynx reading. (The N.L. was factory calibrated before being sent to me).

As you'll see on the attached image there was a sizeable difference between the V.V. humidity and the N.L. humidity a short time ago. Understand the V.V. is ~25 feet above ground level while the N.L. is 5 feet above ground level. I'm also located less than 1/2 mile north of the Tuscarawas River.

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Question is, could there be that much of a difference in 20 feet of elevation? The temperature seems pretty close, about 1.0 - 1.5 degrees difference. So not that substantial.

Opinions?

[CW2274]

I would continue to monitor as dews can yo-yo pretty easily. Use this calculator and see how they do together in a little more time. http://www.dpcalc.org/

[Jáchym]

It is very unlikely the difference would be due to the humidity really being that different.

The analog devices need to be calibrated relatively often, they can be thrown off in terms of accuracy relatively easily. I would in this case definitely trust the Davis more so try setting the value of the analog meter so that it corresponds to your Davis and see if it then mirrors the Davis values. The analog ones lose accuracy over time.

[CW2274]

It is very unlikely the difference would be due to the humidity really being that different.

The analog devices need to be calibrated relatively often, they can be thrown off in terms of accuracy relatively easily. I would in this case definitely trust the Davis more so try setting the value of the analog meter so that it corresponds to your Davis and see if it then mirrors the Davis values. The analog ones lose accuracy over time.

I would hope his "just outta the box" NL would be fairly accurate. Digital sensors drift over time also, as we have no idea how old this SHT11 is. I'd still watch the two over at least a couple of days for a better comparison.

[blizzardof78]

I got it second handed, but it was sent to the factory to be calibrated as well as a new face plate on the temperature to range from -40 to +120. That being said, even when I had it here in my office, the humidity varied by about 10% (too low) when it was literally side by side with my indoor reading on my V.V. I was thinking maybe a micro-climate situation. Often on chilly or cold nights, my Computemp2 temperature drops like a rock as cold air drains but the temperature on the V.V. is as much as 3, 4, 5 or more degrees warmer at 25' above ground level until the cold air "fills" the area. I'm thinking the possible same thing with this. (?)

I'll try a couple of other locations as this was up against the garage on the north side and will call the company tomorrow and see what they suggest. Maybe it's a defective humidity sensor, who knows.

I'm not as concerned with the humidity as I would be the temperature. It's pretty accurate. It's + / - 2 degrees F.

[waiukuweather]

relative humidity is relative
and so you are best to calculate the dew point (from the RH and temperature) and then compare that with the Davis console derived dew point

you will probably then find the difference in dew point is not all that great?

[blizzardof78]

  I kid you not, it's 10:13 p.m. now and the V.V. humidity is at 94% while the N.L. is climbing and at 87%. Tomorrow I'll relocate the solar radiation shield to a more open location and see what that does. I'll be interested in the morning to see what the spread is then.