Dehumidifier hygrometer reads 10% higher RH than handheld meter

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The relative humidity readings are:

49% dehu
39% handheld

That's when they are placed side-by-side in the same area. Could both be roughly accurate with a small margin of error or could one (or both) just be wildly off?
 
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kyphysics said:
The relative humidity readings are:

49% dehu
39% handheld

That's when they are placed side-by-side in the same area. Could both be roughly accurate with a small margin of error or could one (or both) just be wildly off?
Yes. All of those are possibilities. How would you expect us to know?
 
DaveE said:
Yes. All of those are possibilities. How would you expect us to know?
Psychic abilities. :smile: Maybe I should have specified that I'm just curious too how people would handle this?

Buy a third hygrometer? lol Just average them? ...etc.?
 
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Relative humidity measurements at the level of a common, cheap device is more about magic than accuracy.

You should consider those readings equally as 'comfortable'. That'll just fit the accuracy of such devices.

If you prefer to push this to the extreme then as a calibration, you can check the level of comfort according to the readings.

BTW thermometers are the same (to some extent). So just keep in mind that if you wish to know the temperature, then you should never buy a second thermometer, since that'll only bring confusion :wink:
 
Ideally, a RH measuring device should 'equilibrate' quickly - In my experience that isn't always the case. Running the measuring devices side-by-side for an extended length of time might produce a smaller error.
 
Age matters too; humidity meter accuracy drifts/decays over time. I'm not clear on the operating principle, but whatever it is, it is a lot less stable/repeatable than, say, a temperature measurement.
 
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russ_watters said:
I'm not clear on the operating principle,
Stretching hair (human or animal, occasionally spider silk), or assorted artificial fibers in torsion mechanisms, or other mechanical linkages, ...
 
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Bystander said:
Stretching hair (human or animal, occasionally spider silk), or assorted artificial fibers in torsion mechanisms, or other mechanical linkages, ...
Even in a digital meter?
 
Bystander said:
Stretching hair (human or animal, occasionally spider silk), or assorted artificial fibers in torsion mechanisms, or other mechanical linkages, ...
Maybe for the cheap ones. Good sensors use engineered materials and look for changes in physical parameters like dielectric constant or resistivity. Trust me, you won't find farm animals in the production processes of modern sensor manufacturers.

https://www.fierceelectronics.com/components/choosing-a-humidity-sensor-a-review-three-technologies

https://www.sciencedirect.com/topics/materials-science/humidity-sensor
 
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Rive said:
Relative humidity measurements at the level of a common, cheap device is more about magic than accuracy.

BTW thermometers are the same (to some extent). So just keep in mind that if you wish to know the temperature, then you should never buy a second thermometer, since that'll only bring confusion :wink:
re: accuracy relative to price
How would one know the price threshold for accuracy? ...w/o buying the biggest/baddest hygrometer out there (w/ the assumption it's the most accurate)? It's a device I find useful, but wouldn't spend $100 on, for example...$50...mehhhh...okay, I'd spend that.

re: thermometer accuracy
Any data on the margin of error we're talking about for your average thermometer?
 
Btw, I am mainly interested in RH levels for mold growth thresholds (making sure my environment is below those levels). Usually not a big deal to me otherwise.
 
I have two electronic-based hygrometers in the same room about 7 feet apart, they are both an 'added feature' to battery operated clocks. One reads 38%, the other 58%.

A hygrometer in the dehumidifier reads 40%, which experience shows reads low relative to a wet-bulb/dry-bulb hygrometer. (currently out of service because of a mold-contaminated wick :cry:)

Based on the above numbers, I would consider random electronic hygrometers to have accuracy of ±10% of full scale.

Cheers,
Tom
 
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Also since they measure relative humidity, if you are holding your handheld in hot hands it may affect the reading.
 
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kyphysics said:
How would one know the price threshold for accuracy? .
I don't know: never bothered with devices above $30...

kyphysics said:
Any data on the margin of error we're talking about for your average thermometer?
By my experience, for these common/cheap things 2-3 degree (within the usual 0-50 degree Celsius) is pretty common.

kyphysics said:
Btw, I am mainly interested in RH levels for mold growth thresholds
That's a nasty topic, and contrary to the intuitive approach temperature is more important than raw RH value.

We have a wood stove (masonry heater, actually), and at winter RH can go as low as 25-30% (despite any effort to raise it a bit to the not-so-itchy range). And we still has some mold in the corners - mostly, because the comfortable temperature is way too high (around 23 degree Celsius) in this under-insulated house.

Check the RH vs. dew point graphs! Those are the most useful data for mold prevention.
 
kyphysics said:
re: accuracy relative to price
How would one know the price threshold for accuracy? ...w/o buying the biggest/baddest hygrometer out there (w/ the assumption it's the most accurate)? It's a device I find useful, but wouldn't spend $100 on, for example...$50...mehhhh...okay, I'd spend that.
The only way to really know an instrument's accuracy (when new) is to buy something with a published accuracy. For example, here's one with +/-5% accuracy for $27 USD:
http://www.extech.com/products/RHM15

You can find +/-2%, but they are typically much more expensive.
kyphysics said:
re: thermometer accuracy
Any data on the margin of error we're talking about for your average thermometer?
Temperature is much easier to measure. Typically you can find +/- 1-2F (or 1C) accuracy even in pretty inexpensive meters.
 
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