Analog Hygro Charging / Calibration

[palm55]

Maybe I've just been lucky, but I have a couple of analog hygros that actaully out-perform my digital. Unfortunately, the analogs supplied with most humis do not include instructions.

So, for the benefit of those who can't bear to trash the instrument, here's a cut-and-paste of some generic instructions:

Instructions For Your Hygrometer

This hygrometer was designed to measure relative air moisture indoors. It measures the amount of water vapor present in room air as compared to the maximum amount of water vapor that could be present (100%). This hygrometer must be keep in a mildly humid environment to work properly.

Your hygrometer was preset at the factory and will not normally need adjustment. It must be allowed to stabilize for 1-2 days in the environment in which it will be used before attempting any adjustment.

All that is normally required is an initial "moisture charge". To do this, place a damp cloth on the back of the instrument for 20 minutes. This cloth should only be damp because any water droplets that would come in contact with the spring inside the hygrometer would ruin the instrument. Once the cloth is removed the hygrometer should read about 95% (between 90% and 100% is acceptable).

If you find that an adjustment must be made, then do so very carefully. If you look through the back of the instrument you will notice a coil spring that is held in place by a gold color support bracket. This support bracket lies against the dial and has a small tab that comes away from the dial at a right angle (). This small tab has red plastic pin going through it and holding the coil in place. Do not touch this red plastic pin or the coil at any time. To adjust the reading on the dial of your hygrometer, use a small screwdriver to push on the side of the metal tab. This will turn the entire support bracket. The support bracket should be turned in whichever direction will give you the reading that you desire. Please remember that a hygrometer reacts very slowly to changes in the environment. Allow 24-48 hours once the instrument has been located before determining if the instrument is operating properly.