DEW POINT METER:

When compressed air is dried in an air dryer, it is generally used for critical applications. It is therefore essential that the Dryness (moisture content) of the air be checked on regular basis. Most dryers guarantee a Dew Point 40°C or below. This means that only if the air is cooled to that temperature, moisture will condense out of the air.
The Dew point apparatus is a simple device which cools the compressed air and also provides visual indication of the Dew Point temperature. Dry air enters the glass body of the apparatus through a valve of the bottom. It swirls around the brightly polished chrome plated tube and exits the atmosphere at the tip. Either and dry ice is filled in the tube and the mixture is stirred with the help of a stirrer. The temperature of the tube is then measured by a low range temperature thermometer. The temperature of the tube is then progressively lowered by periodic addition of dry ice by the mixture. When the tube temperature reaches the Dew Point temperature, moisture will condense on the brightly polished surface, making it cloudy. The temperature recorded at that time is the Dew Point temperature. As a precautionary measure, the test should be repeated for verification.