Hygrometer accuracy

[MiniatureOrchids]

Hey all, tricky question for you. What hygrometers do you use to track humidity in your terrariums?

Reason I ask is that I bought a reasonably cheap hygrometer on Amazon, and we've been using it for 6-12 months. It often said that the humidity was > 90% despite moss etc feeling a bit dry. Last week, I ordered a new Hygrometer (with a wired probe) and it was reading about 20% lower than our original one, which indicates that all the time we thought the humidity was in the 90s, it was probably in the 70s.

So, after a bit of googling, I tried the salt test last night. I put a bottle cap of salt with some water, along with the hygrometers, into a sealed container for 12 hours. In theory, the humidity should stabilise at 75% and you can get an idea of the hygrometer's accuracy and then compensate when reading it.

But now, the hygrometers (which are in the tupperware tub with the salt) are saying 72% and 74% respectively. The latter reading is the one that was showing as 99% previously.

So it seems like they're both approximately correct around the 75% mark, but diverge dramatically once humidity increases.

So what does one have to do to get an accurate meter? Should I stick with an analogue meter instead? Any recommended and well-respected brands to try? It's no good trying to keep a humid environment for the orchids and moss if we think it's at 90%+ and actually it's at 70% - or vice versa!!!

[Ray]

First, assuming you have a bit of air movement in the chamber, the difference between 70% and 90% RH is probably of little consequence to your plants.

But if you just have to know, get a certified hygrometer.

[MiniatureOrchids]

I guess my main concern is with the general lack of accuracy, can I trust them to tell the difference between 40% and 80%, which would be more critical.

Do you have any links to certified units (otherwise I'll Google).

[Ray]

Google is your friend

[Salixx]

I think we may have bought the same cheapo off Amazon. I have one that is always saying the tank is in the 90's but my home hygrometer says 70's if I put it in the tank. I actually stopped looking at it since the plants are all fine.

In another enclosure, I use an analog Exo Terra hygrometer that's a lot more accurate. Not exactly low profile, but I can hide it in there. If you are looking for a cheap option, it works well.

[estación seca]

An engineer friend tells me they're not very accurate under most circumstances. I think the condition of your mount moss and orchid roots tells you more than the hygrometer dial.

[jdusablon]

Don't know how much this helps, but the DHT11 sensors are very cheap and very accurate, just not fast at updating. I suspect, however, that you're looking for a standalone unit.

[dethswatch]

This is super-accurate:
Amazon.com: BUKE MS6508 Digital Humidity Temperature Meter Ambient Temperature Relative Humidity Measurement Data Hold Data Logging: Kitchen & Dining

It uses a Sensirion sht-75 sensor- you can google for the "datasheet" and see exactly how accurate over a range of temps and H's.

It'll last a coupe days on fresh batteries if you want to leave it on and give you high and low temps/H's too- so that you can get a clear idea of your ranges.

[MiniatureOrchids]

In the end I got one of these: Digital Hygrometer Humidity with Remote Probe 20-90%: Amazon.co.uk: Pet Supplies
Tested it with the salt method, and compared it against two other hygrometers I have, and it looks like they're all consistent and reasonably accurate.