One of the things I do for a living is calibrate room sensors for operating rooms at a local hospital. I regularly spend hundreds of dollars on NIST traceable instruments. Portable humidity checkers are the worst. First, it’s called relative humidity because it varies with temperature. RH is actually a measure of how much water the air can hold. At 85 degrees, you can put a lot more water into vapor than you can at 65 degrees. So, if the temp sensor is off, you’ll never get a good humidity reading. Second, it takes a long time for sensors to settle down. 24 hours in not uncommon to wait for a humidity sensor to give an accurate reading. There is no good answer to this problem. You desire to keep your instruments at a 50% humidity is going to require a humidifier. That way the sensor is always active and it has a way to add humidity to make up for any shortfalls. Air Conditioning has a tendency to remove humidity from the air, so I recommend that you come up with a humidity solution before the summer season gets here. To do a single room, an ultrasonic humidifier is probably your best choice, drawbacks include filling the darned thing at least once a day, and it prefers distilled water, regular water will have a tendency to spread dust everywhere. Central humidification is another option, just don’t think that it’s a device that will run forever, hard water deposits will mean replacing the pad at least once a year, and if you have particularly hard water, you may need to do it every month.

Feel free to add this to the comments. I just can’t remember my password to log in and do it.

Brice Ligget