%RH Hygrometer Discrepencies

[ncognito]

I've had a Lacrosse Technology wall/table digital hygrometer for a while now.  Lately, I've been concerned that it might not be accurate.  What prompted my concern was that over at the UMGF I read a long involved thread on the topic of hygrometer calibration and that many instruments either just aren't accurate, or need to be calibrated by using the "salt test" to determine accuracy so that they could be properly calibrated.  So, I bought a second hygrometer the other day at Walmart; it's made by Springfield Precisetemp.  Both units have new batteries, and neither one appears to be capable of calibration adjustments.  Both are digital, the  thermometer function varies by 1 degree, and the %RH varies by up to 10.  Right now, one reads 40 (Lacrosse Technology) and the other reads 30.  The Springfield unit looks cheap; the other definately appears to be of better quality.  Both are made in China the land of tainted pet food, lead painted childrens toys and poison baby formula; these qualities don't inspire a whole lot of confidence.  What's your experience been, especially you scientist types?

     DAVE

[Randy_R]

do the salt test on both of them. Only then will you know which is more accurate (at least at the controlled humidity of the test) even if they can't be calibrated.

[Mr_LV19E]

Take the unit back to Walmart and get the Acurite model for $7, I bought 2 of them and they both read exactly the same. Better yet they respond to changes very quickly.

Check this thread out, look for the entry by magictwanger half way down the page.

[BluesMan1]

Salt test- fill a bottle cap almost to the top & wet it until it's moist (not saturated). Take a Tupperware container that will keep the cap flat (smaller,better) & carefully place your hygrometer in. Do this where you are not going to move it after everything is in. Put the top on & wait a minimum of 8-12 hrs. (overnight works well). A "perfect " reading would be 75%. From there you use some math to figure out the difference in %. Use some algebra to see what it would read @ 50%. Then adjust mentally or write on a piece of tape on the hygrometer what the difference is (+3,-3,etc.) I have 1 that is dead on, the other 3 I've marked what to add or subtract form the #. Search on the web for more info. Some say don't do this test on digital hygrometers, but I've had no problems. Good Luck !
Jeff   

[ncognito]

Thanks everyone; especially to Jeff (BLUESMAN1) for the directions for the salt test.  Doing the math once the test is done is the simplest and cheapest solution which works fine for me.  It'll be nice to know what the exact %RH is in my music room is.

          DAVE

[magictwanger]

I had the Springfield unit,and returned it for the Accurite unit.I also bought two of them,and am very pleased.

[ark]

I picked up an Accurite today but it read 10% higher than 3 other hygrometers I have, which all were within 3% of each other. My only point is that it is wise to check any of these inexpensive units.
Al

[lyric_girl]

I had a Planet Waves hygrometer and I currently have a hygrometer my father-in-law used for his cigars. Both of these digital units were way off the mark.

I currently have one of these which is a whole lot more accurate.

http://12fret.com/retail/accessories_pg.html

[Randy_R]

Because of this thread I bought one of the Accurite at Walmart.

I have the Accurite, my Radioshack master and the two remote stations all sitting on the table in my livingroom.

The Accurite reads 36%, the RS remotes both read 34% and the RS master reads 33%.

btw, I don't keep my guitars in this room during the winter.

bottom line, shoot for 45% in the room with guitars and these discrepencies won't matter.

I suppose I should try to obtain a calibrated humidity gauge that I can compare with, or calibrate one myself using the salt test.

[bud0505]

I bought a  Springfield unit from Walmart and ran the salt test on it. The unit tested minus 12% and it is non adjustable. I have read reports on forums where people had good results with them......

[BluesMan1]

I have 2 Planet Waves & did the salt test on both. One was right on, the other 6% under (@50%). Using the deviation @ 75% for the good one, I calculated what it would be @ 50%. I know 42-48% is recommended, but better to be a little over hydrated than under. I just add 6% to the other one to get a reading. I just went out & bought 2 HumiCase hygrometers, which are both right on the money. They were $25, compared to $35 for the P.W.'s. Check them out. The others might be cheaper, but down the road, you get what you pay for.
Jeff

[bluesman67]

Not to rain on the salt test parade, but finding out that a hygrometer is accurate by calibrating it to the humidity of salt does little to ensure the accuracy of that hygrometer in the 45-55% range that you want your guitars to be in (IMO).  What would get you more accurate is owning 2 or 3 different hygrometers and taking an average reading and also give you peace of mind.  I have an Oasis that I bought from www.elderly.com that seems to be very accurate. 

[BluesMan1]

Yes, but knowing what your hygrometer should read using the salt test helps you calculate what it should be @ 45-55% range. How do you know which one is reading right if you don't have a starting point for accuracy ? If it reads 73% after the salt test, it will read about 50% when it should (give or take 1%). Close enough to work with & figure out how the others should read. The deviation of the others is then added or subtracted from the one that's right on. I put a piece of tape on the one's that are off & write "+5,-7,etc." then know what to add or subtract from that one. How do you know any of your hygrometers are correct just by taking the average ? To simplify things, bring them to a music store with an acoustic room that is climate controlled & see what they read. Then you can do the same thing with the #'s. You just have to be within the range you mentioned. Remember, these %'s are accurate @ 72 degrees.
Jeff   

[bluesman67]

  I don't know, I guess I would tend to trust an average more than a salt test that isn't really the humidity level that I'm shooting for.  Actually, I assume mine is accurate because my guitars look and feel right.

[rick ch]

The weakness in the salt test calibration is that the error of the hygrometers (especially the inexpensive ones we use) is not linear, meaning the error at 75% humidity and at 40% is often different.  That said, the difference in error at different humidities shouldn't be huge, so the salt test isn't totally useless.

[BluesMan1]

I agree. But by doing the salt test, you get the percentage of error & the differential #, which then can be calculated to any R/H% you want. These things (hygrom.'s) are just a close reading to the actual % @ 72 degrees. They will read differently @ different temps.. The error increases as you adjust for lower %'s, so you anything close is good enough. Like I said before, just bring them into a climate controlled room @ Sam Ash, Guitar Center, etc. & check them with their reading. Then you'll see just how far off some of these things are ! Some say the salt test will screw up your digital hygrom., but I have not had that happen yet. Probably the salt vapors getting into the electronics.
bluesman, I didn't have a hygrom. until about 2 years ago. Never had a problem, just used my Dampits (filled twice a week). Now with the gadgets, I'm more anal about the humidity. If your gits seem right, just do what you're doing. I always sight down the neck anyway to see if the top of the bridge is even with the end of the fretboard. If the bridge is low, it needs water. If it's high, just back off a little on the water. Better a little too much than not enough !
Jeff