Measure dew point and relative humidity with this easy-to-use sling psychrometer. It includes two thermometers, wet bulb wick, handle and instructions.
When you are using a sling psychrometer to measure relative humidity in an area where there is a large difference between air temperature and humidity levels, it can be more difficult to achieve consistent results. It is important to use a very consistent procedure.
First, make sure the wick is tied tightly around the bulb of one thermometer, using a rubberband at both the top and bottom of the bulb to secure the wick. Make sure the bulb is covered as completely as possible, at the same time leaving the widest possible amount of wick exposed to the air.
Because of the high temperature and low humidity levels, it's easy for the wick to dry prematurely. You'll need to make sure that the wick does not dry out by the time you've taken the reading; you could try using pre-cooled water to keep the wick from drying out as quickly. Be sure to read the wet bulb temperature first, as it will change quickly. Swing the thermometers for at least one minute, but not much longer, before taking the reading.
Altitude can have an effect on the reading of the psychrometer, since the provided chart is based on sea level. If you live at a high altitude (2500 ft or more), we recommend that you search the internet for a high- altitude chart or correction factor.
There is also a possibility that your thermometers are not measuring accurately. Do they read within two degrees of each other when left at room temperature? If one is reading higher that the other, you can add the difference to the other so that the results will be adjusted correctly.
Typically, you should take at least three readings and compare them. If there is much variety in the results, your procedure probably needs to be more consistent.
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