Hygrometer Calibration - instrument care

[Dave Martin]

https://www.neptunecigar.com/tips/ho...our-hygrometer


This provides guidance with these steps:
1. 2 teaspoons salt in a small container, dampened -- not dissolved -- with water
2. Seal this in an airtight see through container wait 6 hours at least
3. Instrument should read 75% RH inside the container. A difference is the amount +- that needs adjustment.

Comments? Suggestions?

It's been pretty darn dry in these here parts.

Dave Martin
Santa Fe, NM

[HoGo]

You got it right but I prefer using magnesium chloride instead of table salt and expect 33% humidity. For instruments the lower range of humidity is more critical than the upper. For cigars 70-75% seems to be the norm. There are other salts for testing other levels. If you use damp spnge only, you should read 100% or very near.

[DHopkins]

Or, for easier cleanup, try this:

https://bovedainc.com/store/tobacco/calibration/

They're in the business.

[HoGo]

Or, for easier cleanup, try this:

https://bovedainc.com/store/tobacco/calibration/

They're in the business.

You can get quite a lot of salt and plastic bags for $7...
You can buy 2 pounds of MgCl for that price...

[DHopkins]

You can get quite a lot of salt and plastic bags for $7...
You can buy 2 pounds of MgCl for that price...

You make a good point, however, "They're in the business" and have been for several years. Their products are certified for lab use. That said, I seriously doubt that precise measurements are necessary for any hygrometer used for musical instruments and the "home brew" would work just fine.

I was mostly just showing a pre-fab alternative.

[Mandobart]

I was an electronics tech in the USN. Maintaining the instruments to monitor and control a submarine nuclear propulsion plant was my job for almost 9 years. I now work as a senior reactor operator at a nuclear power plant. I work closely with our instrumentation and control techs.

The procedure described in the thread is NOT a calibration. Its a single point cal check. A calibration sets the instrument zero, span, linearity (if applicable) and confirms tolerance throughout the indicating range using 5 cardinal points. This provides confidence that the instrument is providing accurate readings throughout its range. Calibration needs to be repeated at some frequency since all electronic instruments drift over time. Calibration returns the instrument to standard performance and accuracy by actually adjusting the response from sensing element to output indication/control function.

The "salt check" for a hygrometer is a single point cal check. All it tells you is how accurate the instrument reading is at one point (75% RH). There is no reason to expect the same accuracy throughout the instrument's range. There is no way in most consumer electronics to adjust the instrument output if the reading differs from the standard. If you keep your relative humidity around 75% then this cal check may be helpful. If you prefer an RH of 40 - 50% you still don't know how accurate your hygrometer is in that range. It would be incorrect to assume that if your hygrometer read 78% in the salt check you should then subtract 3% from all readings throughout its range - you don't know enough about the instrument's circuitry, designed response, linearity, quality of your salt solution, etc. to make that assumption.

Here is a simpler way to do a single point cal check - I recently checked my Extech hygrometer by putting it outside. Per my phone local weather app and weather underground the RH was 64%. The Extech read 62%. Being as reported weather data usually comes from a local airport which is ~4 miles from me and reported no more frequently than hourly, I consider this reasonably accurate. This can be repeated over a range of actual outdoor RH values to get a better idea of how your hygrometer performs.

[pops1]

Mine is mechanical and not electrical, like Bart says it is not a calibration, but a check. I also clean the dust inside as air needs to go by the coil to sense the humidity and if there is dirt or dust there it will hold onto the moisture and give you a false reading.

[Mandobart]

It's been pretty darn dry in these here parts.

Dave Martin
Santa Fe, NM

My family is from Raton. My grandpa was a coal miner up there from around 1910 through the 40's. He had an 1880's German trade violin that he played for dances. Later he gave it to a niece. Many years later it went to my dad, in Los Alamos. About 5 years back it came to me. This violin had never known humidity or humidification. Not a crack, separated seam, loose parts, nothing. I also grew up in Los Alamos completely ignorant of stringed instrument humidification. I still have my violin and guitars from that time. Again, zero issues from low humidity. I played in orchestra and a few bands and never met anyone who experienced any of the horror stories we read about online (cracks, splits, etc.). Now I live in a different type of desert (shrub-steppe) with higher humidity than northern NM, but I use room humidifiers to keep my music room between 40 - 50% RH. Like strings, picks, pickups, tone-gards and tone-rites we've said more than there is to say about humidity and humidification, but we keep coming back to discuss it.

[DHopkins]

Like strings, picks, pickups, tone-gards and tone-rites we've said more than there is to say about humidity and humidification, but we keep coming back to discuss it.

First, your method of using the weather bureau is easy, cheap and certainly accurate enough.

Second, yeah, we discuss it a lot...probably a lot more than it deserves. Hydrating musical instruments is not an exact science. If you compare your hygrometer with the weather bureau, that should be enough calibration. I believe we're assigning more importance to precise measurements than is necessary. This isn't Mandobart's submarine. It's horseshoes (or dancing). Close counts.

[HoGo]

I have seen enough cracks on instruments caused by low humidity. This is quite random thing, some instruments seem indestructible while some will react wildly. Depends on how fast the changes occur and during this time of year also method of heating is huge factor.
If instrument lives it's whole life in low humidity and didn't crack at the beginning (perhaps because it was made under similar conditions) then it likely will survive it unless the humidity changes from low to high and suddenly back. My workshop is humidity controlled and I wouldn't go back. Just imagine if someone's instrument cracks while with me... could be disastrous and hard to explain to owner that there was sudden humidity drop caused by weather...
I've got old-school hair hygrometer where range as well as scale can be adjusted. I check at 33, 75, and 100% and when I get these three right then the whole range is good enough for me.
Folks have tried the salt check and ordinary salt is perfectly suitable, no need for pharmacy grade pure stuff. But for instruments simple check at 33% is preferrable as the low humidity (below 40%) is more danderous than higher levels.