HUMIDITY SENSORS

Relative humidity is defined as the amount of moisture in the air compared to the total amount of moisture that the air could hold when it's 100% saturated. It's important to understand that as air is heated its ability to hold moisture increases. The amount of moisture in air is important in industrial applications like printing and environmental control of computer rooms or clean rooms where solid-state integrated circuits are manufactured. Other industrial applications where humidity is controlled include painting applications and plastic injection molding and extruding. The moisture content of the raw material in plastic injection molding and extruding must be controlled because the moisture turns to steam at the high temperatures during the injection process and causes unwanted defects in the surface of the parts. In printing applications the humidity in the press room must be strictly controlled to maintain approximately 40% humidity. If the humidity is too high, static electricity builds up as the paper moves across the platens and press rollers and the static charges will use the moisture in the air to move from the paper to the metal of the presses. These static charges are dangerous and can cause fires or explosions when they jump, or they can injure personnel who are near.

Since relative humidity is dependent on temperature, most relative humidity sensors have temperature measurement devices built in or added to them. After these sensors have determined the relative humidity, their signals are generally used in feedback systems for dehumidifiers or humidifiers. If the relative humidity is too high, a dehumidifier is used to remove additional moisture from the air. This is accomplished by passing the air over a cold surface such as an air-conditioning coil. If the temperature is below the dewpoint, the moisture in the air will condense and form moisture droplets that can easily be collected as gravity pulls them to the lowest part of the coil where they go down the drain.

GAS DETECTORS