Slimboli
not inappropriate or out of place. i just don't understand why a tolerance of 10% is considered
accurate. you are correct the digital should be more accurate but having calibrated all my digital
and analog hygrometers, i can put them all in the same box and they will all read within 1% of
each other.
i guess i didn't explain the digital calibration technique properly.
the calibration for both digital and analog is exactly the same, damp salt in a sealed bag and the
humidity should read 75% on the device being calibrated.
with an analog, you turn the adjustment screw on the back, with a digital you have to get into the
inner working and find what i called a potentiometer, used in the loosest term.
a potentiometer refers to a sensing device that measures and can adjust electrical current, like
volume from a radio. (do they still call them radios?)
in a water heater it's not called a potentiometer but a thermocouple, and it measure and adjusts
for temperatures, set the temperature of the water you want, and the thermocouple maintains it..
i don't know what it is called in a digital hygrometer, but it works on a similar principle, except it
only measures the humidity but does not adjust it.
the reading on a digital hygrometer can be adjusted using the calibration screw on the "pot"
located inside the case using a jewlers screw. some digital hygrometers will come with calibration
instructions with a picture showing where the pot is located.
this is from http://www.cigargroup.com/faq/
6.2 Radio Shack #63-855 Calibration
Ok! Feeling "scientific after testing the calibration of your hygrometer? Well, the next step for the
ambitious among us is to actually callibrate our hygrometers. Many cybersmokers use the Radio
Shack 63-855 Hygrometer, (also known as the "Airguide" Hygrometer). The following procedure
was written specifically for that instrument. Please read these instructions very carefully before
proceeding - If you don't feel comfortable tinkering with sensitive circuitry, DON'T DO IT!
Now that you know how far your instrument is out, you might want to adjust it. CAUTION! Mess-up
here, and you could damage your hygrometer! There is no simple calibration knob to turn. To
adjust this instrument, you'll be re-adjusting the bias current of the sensor, then comparing it to
your calibration reference - the salt in the baggie.
Remove the battery door, the batteries, and finally the back of the unit. along the top edge of the
PC board inside, you'll see two round, flattish metal disks (micro-potentiometers). don't touch the
left one, you'll be working only with the one on the right. First, look at it closely. You'll see a tiny
indent for a tiny screwdriver blade across the middle. Sketch its exact position carefully - this
procedure might take several days, and you will forget the original orientation if you don't write it
down!
You'll be turning this right potentiometer (pot) a tiny amount to change the humidity reading (1/8
turn might change your reading by 3 or 4%). DO NOT turn it more that 1/4 turn! Use a very small
screwdriver (like a jeweler's screwdriver), and don't change it by much! If you were reading above
75% in the calibration test, turn this pot clockwise, again only a tiny amount... If your reading was
low, turn it slightly counter-clockwise...
You can leave the back off to save some effort, and put the batteries back in now. Be sure the
"min" and "max" functions are turned off, and place the hygrometer back in your baggie with the
salt. Again, let it stabilize for 6 hours, and DON'T LET IT TOUCH THE WET SALT! Check your
reading, and re-adjust if necessary. Be patient, you may have to try a few times to get it right. If
you feel you're getting nowhere, set the pot back to exactly where it was when you started.
When you're satisfied with your setting (set it to +- 1% of 75%) remove the batteries, re-assemble
the unit, and give it one final check. Once you're done, light up one of your best cigars - you'll
deserve it!
Radio Shack #63-1013 Calibration
The Radio Shack model 63-1013 hygrometer can be calibrated similarly. The potentiometer (pot.)
can be found on the upper left hand side of the circuit board once the back is removed. The pot. is
small -- about half the diameter of a pencil eraser. The pot. has a small slot in it to allow for
adjustments. Clockwise turns increase the humidy percent reading and counter clockwise turns
decrease the reading.
6.3 Older Radio Shack units
contributed by Steven Banks
I would like to add some new information. I have one of the older Radio Shack hygrometers #63-
844, but do you think that stopped me? You give me an opportunity to take something I know
nothing about apart, I'm there! Plus, my Dad was a quality assurance engineer and he wouldn't
have put up with that much of a error factor.
Well the salt portion of this whole procedure is sweet indeed - so simple, I felt like I was watching
"Mr. Wizard" again. After doing this I found that my hygrometer was a whopping +8% off. Now...
I'm not great with math, so I decided to correct the problem instead of just knowing how much it's
off by. The problem was, which "pot" screws to adjust, since the instructions were for a #63-855.
Well for those of you that have the same model as I do, there are two circuit boards in it, the top
one is for the temperature and the bottom is for the humidity. The "pot" screw CLOSEST to the
battery compartment is the one you need to adjust. And yes, as was mentioned in the first posting,
it does take some fiddling!!! There were times I'd adjust the screw, and see no change. But I
finally got that puppy within + -1%. Note that this hygrometer's reading will INCREASE as you turn
the control CLOCKWISE - exactly the opposite of the 63-855 model...
Let it be known that I tinkered where no person in their right mind should, and this is no guarantee
that it'll work for you (especially knowing Radio Shack stuff - yours could be laid out differently?)
But if you're bold, go where no man has gone before and make it right!
