Hygrometer Calibration - High and Low RH

[RichG]

I suppose this ties slightly into the OCD elements of cigar maintenance discussed on that other recent thread. 

I recently calibrated a handful of Oasis Caliber IV hygrometers using a Boveda 32 calibration bag. The results were generally outside of my expectations. Essentially I had to lower the baseline on all of my hygrometers 3-5 points, when I felt they were performing rather accurately to begin with.

Feeling generally suspicous of this outcome I ordered a Boveda 75 calibration bag. I just left one of the adjusted hygrometers in overnight, and I am seeing that according to the new test I need to raise its reading by 6 points.

My thought is that I should probably calibratre to the 75RH as its much closer to an actual storage value. I was wondering if anyone had any insight to share on hygrometer variance over these kind of RH ranges, or had any thoughts on the matter involving 32 vs 75 calibration.

...and yes I know...I probably should have left well enough alone!

[williamthewolf]

I've calibrated 7 or 8 Caliber IV's in Boveda RH75 calibration bags as well as with 69 and 65 RH packs in triple bagged ziplocks. Not one of mine needed manual adjustment. Boveda confirmed with me via email several months ago you can use any air tight bag with any RH pack of your choosing. How long did you leave the hygrometers in the bag w the 32 pack?  What temperature was the room?

Edit: I see you tried the 75 bag already.  I don't know what to tell you. Maybe your hygrometer is a dud. Can you send it back for a new one? 

[gormag38]

Typically when doing a calibration on any instrument, choosing multiple calibration points will ensure that your calibration curve meets more accurately along the whole range of your instrument's readings. If you were able to calibrate at 30%, 60% and 90% your curve would be more accurate than if you just calibrated it one of those points.

HOWEVER with most hygrometers that I'm aware of, I believe a one point calibration is all that you're able to do. So in your case I would think setting your calibration curve using a point that is most closely to your suspected conditions would mean it would be most accurate at that point and less accurate as it traveled to any other extreme on that curve. 

Hope this helps! 

[Ites]

I've only really used the good old salt test methods for calibrations and generally they take time to stabilise. Especially for passive sensors without fans and even more so when the sensor is closed in. Generally I would use sodium chloride for 75% readings and potassium carbonate for 43% readings in the "common room temp" environment. I find boveda to be quick to "respond", but I would suggest trying again with a longer time than just over night. I would start out with the 75% (either bag or salt, doesn't matter) and calibrate your sensors. Then if you want the extra step, try it with a different one and if the second reading isn't correct to your new calibration you should consider getting new ones. Bare in mind the +-1% error in the sensor, on both readings. Also, I believe boveda has a +-1% tolerance too. So in principle you could read 73-77 and still be within range. 

 

Personally I would aim for 75% and 65/62% because that's around the range you'd normally use the sensor in.

[RichG]

12 hours ago, williamthewolf said:

How long did you leave the hygrometers in the bag w the 32 pack?  What temperature was the room?

They were in the bag for quite a while, in some cases days from what I recall. The room is constantly around 66 deg.

12 hours ago, williamthewolf said:

Maybe your hygrometer is a dud. Can you send it back for a new one? 

It’s five or six hygrometers with similar results.

11 hours ago, gormag38 said:

So in your case I would think setting your calibration curve using a point that is most closely to your suspected conditions would mean it would be most accurate at that point

11 hours ago, Ites said:

Personally I would aim for 75% and 65/62% because that's around the range you'd normally use the sensor in.

Thanks for the thoughts. I am going to go back to calibrating all of the hygrometers using the 75, as this aligns much more harmoniously with the factory calibrations of the units as well as my expectations of what the RH should be in my containers based on storage conditions. 

[GoodStix]

Boveda recommends the 75% kit for calibrating cigar hygrometers (closer to storage conditions).  They also recommend not using the RH storage packs for calibration.  They say those have greater variance than the calibration kits, which they claim are more accurate.  (I don't know for certain.  I just use the kits as they recommend.)

The main B&M retailer in our city has been using the Boveda 75% kits for many years for all of their hygrometers.  They recommend using the kits at room temp 70F and leaving your hygrometer in the kit bag for 3 days to get a more accurate reading.

[BossHogg]

I just calibrated all my oasis caliber IV's, my Govees, and ink bird using the salt test. I did this test multiple times over several days.

All of the hydrometers were 4-5 percent below what they should have been reading. So that means my humidor that was reading 65 was really at 70 😲

Changed all my hydrometers to reflect the actual 75rh from the salt and then retested them. My cigars are smoking wonderful now 👍