Indoor Air Quality Training
Dry bulb and wet bulb thermometers both indirectly measure the amount of humidity in a given volume. The dry bulb thermometer measures the air temperature while the wet bulb thermometer always gives a lower reading because of the cooling effect that is produced from water evaporating over the covered thermometer. The thermometers could be placed in a Stevenson screen (which is an is an enclosure to shield meteorological instruments against precipitation and direct heat radiation from outside sources, while still allowing air to circulate freely around them), they could be whirled together in a sling psychrometer, or they could be ventilated by drawing air past them through the use of an electric fan. The readings and primarily the differences of the temperatures produced by these methods enable the humidity to be calculated.
Hygrometers are the easiest and the most accurate way of quickly measuring ambient air and relative humidity levels. Generally use the resistance of a sample of air to calculate humidity. Specifically, capacitive hygrometers contain two metal plates separated by air. The more water that’s located within this air volume, the more affected the plates ability to store a static electric charge will be. Through measuring the maximum amount of charge that can be stored, the amount of humidity can be determined. An electric current flows through a piece of ceramic which is exposed to the air. The higher the humidity of a given volume is, the more water vapor will be condensed inside the ceramic. By measuring the amount of current that flows through the ceramic, the amount of humidity will be revealed on the digital readout on the screen in seconds.
Moisture meters are used to measure the percentage of water in a wall and determine the amount of humidity that is present. Electrical power is easily conducted through a moist or wet environment. When wood fibers contain moisture it can also conduct an electrical signal or voltage. This allows the moisture meter to act as a signal generator. The signal generator will output a small voltage into the wood fibers. The small voltage is typically supplied by a battery . The moisture meter contains an internal circuitry much like an ohmmeter. The ohmmeter reads the amount of resistance that an electrical circuit may employ in conducting electricity. Resistance is the opposing force to efficiently conducting electricity. The moisture meter will send a small voltage into the piece of wood being tested. The voltage is conducted into the piece of wood through two very sharp pins. These pins are set a specific distance apart from each other and when the test button is pushed the meter can read the resistance between these two pins. The resistance of the wood fiber circuit is then transferred to an indicator, to reveal how much humidity is present and if it proves to be too high, it may be permanently damaged and the affected area (wall, floor, etc.) must be removed completely.