favorite and ACCURATE humidity meter?

[SLTA]

For those of you who do work with existing structures, or who collect guitars or cigars, do you have a favorite hygrometer? I would like to have an accurate number on humidity and temperature when I'm in crawlspaces but am having trouble finding a reasonably-priced and accurate monitor.

cheers!

Please remember: we're not all guys!

 

[btrueblood]

SLTA,

Accurate, eh?

The trickiest thing about hygrometers is that they don't stay calibrated for long, and it's worse when they get dirty. Buy one that has a replaceable element (and from suppliers that will recalibrate them for you, or send you calibrated replacement probes), and expect to pay somewhere north of $300.

Or, buy a sling psychrometer if you can find room to swing one in a crawl space.

 

[EngineeringEric]

Ie had good luck with one from ThermCo products, i think it is the Supra! it has a little sleeve to protect the element... but i don't bring it into crawlspaces... i have used a wood moisture meter (prongs) in crawls but those are more robust and you can calibrate them yourself.

 

[dhengr]

SLTA:
And, in fact, what you are really interested in is the MC of the wood, not the ambient humidity in the crawl space. You can feel that, whatever the exact value, and you should advocate for some controlled venting to settle that moisture level down. However, venting a crawl space is a difficult thing to get right, because of the difference in inside and outside temps. and dew points, and because of the wicking-up of moisture from below. Sometimes drawing outside air into the crawl space actually increases the relative humidity, and defeats the purpose. A strong argument can be made for conditioning the crawl space and moisture proofing it so you can control the moisture. But, that costs money too.

 

[Ron]

SLTA .....rather than taking spot measurements of humidity I would use a USB data logger from Extech or ThermoWorks. I've used both with good results. You can set them to log every few minutes and you can get a spectrum of the humidity and temperature variations in the crawl space to make better decisions on the need for venting. As dhengr notes, checking the moisture content of wood items in the crawl space is important as well. We use both Delmhorst and Protimeter moisture meters with traceable calibrations.

 

[Compositepro]

I have had this psychrometer for almost 40 years:

https://www.amazon.com/Cole-Parmer-...qid=1500777540&sr=8-168&keywords=psychrometer

It was difficult to find it on the internet. It is basically a sling psychrometer except that it uses a small battery powered fan to move air past the wick on the wet bulb. While other hygrometers are more convenient, I do not trust the calibration being stable over a long time. Without a fan, any hygrometer can take a long time to reach a stable reading.

 

[Spartan5]

+/- 2% RH, Under $30, supports continuous logging with remote data recovery/monitoring via bluetooth. Runs for months on that battery. Super responsive.

https://www.sensirion.com/en/environmental-sensors/humidity-sensors/development-kit/

https://www.digikey.com/product-detail/en/sensirion-ag/SHT31-SMART-GADGET/1649-1024-ND/5872239

You may need/want to build your own enclosure/case.

The sensor that is built around is used in higher-end weather stations.

 

[SLTA]

Thanks, everyone.

Please remember: we're not all guys!

 

[btrueblood]

FWIW, our company builds a logging humidity sensor for use with our products, and I went through a variety of methods to calibrate (or at least prove) the sensors. It's a pita to get a good, accurate reading in still air, or to get a good, accurate reading of any airflow with which to calibrate the capacitive type sensors; any contamination in the sensor filter will likely skew the sensor reading if there is not sufficient dyanamic pressure to push the airflow through the filter. I struggled with saturated salt solutions which take forever to reach equilibrium, before realizing in a couple of cases that the filter body I'd used was likely contaminated by being handled by numerous people whose salty sweat had rubbed off onto said filter, and that salt was skewing the reading away from the expected value from my (different chemical) salt. IF you are careful, you may be able to avoid getting any kind of salt into your hygrometer housing (good luck with that if you live in an area that gets dusty occasionally). Again, the quickest, most accurate and reliable method is still to sense the condensation temperature (dewpoint). Or basically, what Cpro said.

 

[btrueblood]

Sorry, got interrupted before finishing -

The issue with contamination is that the sensor portion of the typical capacitive sensor used in handheld/logging devices is a tiny, itty bitty little silicon chip, typically with a tiny 0.01-in^2 gore-tex filter patch over it. If even a grain of regular sodium chloride salt lodges against that filter patch, it will act like a saturated salt solution, absorbing moisture from the air that is above its saturation RH, or giving off moisture when the air is below its saturation RH, and in both cases skewing the actual RH of the air that reaches the chip's sensor.

In laboratories where RH control to within a few percent is required, a chilled mirror hygrometer (essentially an automated psychrometer) is usually specified, as it delivers the required accuracy and traceability. If capacitive sensors are used, they will have their sensor element replaced or recalibrated on 6 month to 1 year intervals.