Thursday, January 19, 2012

Measuring the Dew Point

Measuring the Dew Point

Environmental conditions can determine the effectiveness of many industrial applications, which is why monitoring the dew point is essential in many trades. For example, the dew point, defined as the temperature at which air moisture begins to condense, is a significant factor in HVAC, heating, venting and cooling technologies. It is also important in determining potential corrosion in metals, and in numerous chemical manufacturing processes. Because of its vital role in vast processes, precise dew point measurement tools have become a fundamental utility in everyday industrial functions.

Effective Dew Point Tools: Hygrometers

Generally, hygrometers, or cooled mirrors, have been the conventional tool used for precise dew point measurement. The device is considered to be a humidity transfer standard. The process entails cooling a mirror until water vapor begins to condense on the surface. The temperature of the mirror is measured. This projects the dew point of the air. This process is generally used in laboratory practices, and for monitoring the environments of storage venues. In addition to its use in material production (paints and glass manufacturing, for instance), the system is also effective in dry food processing.

While the mirror system is widely considered to be the most effective measurement process, its drawback is a tendency to become polluted. Because the apparatus is sensitive, it is necessary to clean the device to ensure continual results, but it may be costly to maintain. Inspection and maintenance can be performed with a mirror microscope, and typically the sensor can be opened manually via attached springs. Modern measuring hygrometers that have developed from the first manual chilled mirror hygrometer include more elaborate models, such as “self-checking” features that allow the device to detect and react to contaminants. Also, these devices are available in digital and allow for wireless readings. This process allows the device to be an equalizer of the condensation and evaporation on the surface of a mirror by using an electronic mechanism.

Lithium Chloride Sensors

Lithium chloride sensors are used because of their high reliability and relatively easy construction. They are advantageous over electrical humidity devices because they are not easily contaminated. Industrial uses of this device include measurements for dryers and refrigeration controls. In these applications, each sensor is composed of metal tubing walls saturated with lithium chloride solution and wound with wires that are connected to a power source. The device is not easily contaminated, and may be cleaned with ammonia and recharged with lithium chloride. Generally these sensors are used for industrial uses that require moderate accuracy.

Aluminum Oxide Hygrometers

Another common device for dew point measurement method is metal oxide apparatuses, also known as aluminum oxide technology. These devices are typically designed for low dew point measurements. They are generally small in size and can often be placed on walls or ducts in industrial settings. These sensors are effective in a wide array of industrial uses, as their multiple sensor features allows for a broad measurement range. Metal oxide hygometers are typically less accurate than the mirror device and are not considered efficient for long term use. The sensors are susceptible to environmental factors can be easily destroyed if they are exposed to damp conditions. Because of such sensitivity, regular assessment and recalibration of the tool, (often by the manufacturer) is necessary.

Polymer Sensors

Polymer sensors have been long used to measure the dew point and are also effective in calculating a wide humidity range. Typically applied in power industries and to measure petrochemical processes, these sensors are generally used to measure low dew point applications. The notable advantage of this application is its long term stability and efficiency in processes that require minimal maintenance.

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