Digital isn't always better

[Lillian]

I bought a Caliber III to monitor the RH in my shop. It had good reviews and the price was right. I needed a clock so I grabbed a cheap wall clock with thermometer and hygrometer. I figured it would take a day or so for it to settle in. Well, after a week of 13-15 points difference, I decided that I needed a better analog hygrometer. So I found one that reports to use a hair. Within few hours the two analogs where within 3 points of each other, leaving the digital way below. After reading that some hygrometer are only accurate within a certain range, I decided to bring the shop's RH down to about 50% according to the analogs, hoping that the three would get closer. Nope, the digital was still way lower. Life got busy and I left the shop sitting at the analog's 50%. I watched as the top and back I had joined curl and then flatten after flipping them. It stopped after two days.

Enters JJ's post on making a sling psychrometer. The two thermometers arrived from 4physics.com yesterday. The analogs are basically correct. The sling psychrometer split the difference between the two.

For $13 and two pieces of tape, I have piece of mind and can start gluing.

Thank you JJ for taking the time to post.

[Craig]

G'day Lillian,
I have a digital ( StewMac ) and don't trust it either. It's proven to be incorrect too many times .

Here is one I made from 6 strands of my daughter's hair ( 9 " long ) It works on the same principle as the most sensitive ( and expensive ) hygrometers available .
Human hair is the most reliable medium known to man for measuring humidity.

This little unit , although rough around the edges , has proven to be the best and most reliable of all

[Lillian]

I've admired your ingenuity for a long time. I thought about making one like yours, but didn't believe that I would be able to make one that was accurate.

[Paul B]

No inlay?

[Craig]

I've admired your ingenuity for a long time. I thought about making one like yours, but didn't believe that I would be able to make one that was accurate.

It's the hair that's accurate Lillian ,,,, not me !

Here's a link to the Franklin institute on how to make one.

http://sln.fi.edu/weather/todo/hygrometer.html

I tied the end of the hair strands to an eye hook at the top of the guage . This way ,I could make an adjustment to the hair length by winding up the strands until I have it calibrated


No inlay Paul Getting slack huh ?

[Lillian]

Craig, how did you calibrate it?

[Taffy Evans]

Hi Lillian
Iv'e got the Stumac digital and an old anolog version. The other week it was so dry it stopped displaying, just a row of dashes. I got a bucket of water and a fan blowing across it and found that when the MC of the room got to 15% [according to the digital device] it started recording again. On another occaison the humiditay was reported as 90% plus for our town but the reading was about 80%. So I'm going to hit up the grandkids for some hair.

[Lillian]

Fran's hair is definitely long enough, and she leaves them around the house, so I don't have to sneak up with scissors. It's the calibration that's got me, especially the low end of things.

Now that I have the sling psychometer, it isn't a big deal.

[ap404]

Brilliant Craig,

Well, I'm going to have to try this but i'm bald as and my lady friend has corkscrew hair ( notoriously sensitive to weather ). I wonder if the curls will interfere with the readings ??

I might have to go for 10c of ballast instead of 5 ...

Cheers

[Craig]

Craig, how did you calibrate it?

That's the tricky part I suppose, but here's how I went about it.
Soak the hair in water. This gives one extreme . Mark that spot. Now dry it completely with a hair dryer . This will give you the other extreme. Mark that spot also.

Measure the midway point between these two marks . Call this 50 %

From there , I fine tuned it over a period of time by comparing with radio weather reports and other hygrometers etc . I now have it to a stage where it's about right. I've become very fond of it !

Seeing as you have a sling psychrometer Lillian , I'd compare it to that for a start.

In my opinion I don't think it necessary to build to an exact number such as 43% ,,,,,,,or 44 % or whatever . I'm happy if it's between 40 to 50 %.
Instruments will go through all sorts drastic humidity changes during it's lifetime . If it's built within this midway range , I'm sure it will cope . All those early master builders never had a digital read-out.