Moisture test in pure areas

The choice of the correct measuring instruments is for reaching optimal results of measurement of greatest importance. This is valid also for calibrations, in regular� Distances accomplished and on restorable standards to be based should. A multiplicity of products, including pharmaceutical products and semiconductor, are manufactured in pure areas. Usually dampness, temperature, and pressure are supervised particle content, there these parameters substantial influence on the quality and those� Productivity to have know. Relative FeuchteDie rel. Dampness (rF) designates the portion of the water vapour of the gas mixture of an environment. It indicates the relationship of the momentary steam content in an area to the maximally possible steam content at the same temperature. Procedures such as expansion and contraction, a confirming and a softening of materials to produce change of the viscosity of a liquid, growth of microbes, rise of of the static electricity as well as corrosion and corrosion to a large part by the dampness affect-dew point-affecting dew point that dew point (Td) is the temperature, on which a gas mixture will be cooled down must, in order condensation. The dew point is size, with very small quantities of water in a gas mixture, as can be e.g. indicated air. During the micromachining of semiconductors very dry conditions prevail, since water molecules are regarded as impurities. Under such� For conditions is appropriate rel. Dampness practically constantly with almost 0% rF, on the dew point scale however also smallest changes of the water content in the measured gas are easily provable. Different uses, different requirement manufacturers of pharmaceutical products usually have a large number of pure areas. The control and recording of temperature and dampness are subject to the strict rules of the GMP (Good Manufacturing Practice). The most important characteristic, which is demanded by damp sensors, is a high accuracy. It is extremely important from there, precise calibrations would drive through to be able, in order to place surely that the sensors exhibit no measured value drift on a long-term basis. In the food processing industry the dampness must lie in the production areas at a certain value or hold below a value. Like that are values of bspw. 40% or lower generally usually. Thus growth is limited by germs and bacteria, which can lead to food poisonings. During the semiconductor and the electronics production the distance between the product generations becomes ever shorter. From this it results that the monitoring of the dampness and/or the dew point in the production process become ever more important. In the mini Environments of the manufacturing plants ever more frequently highly exact measuring systems with deviations from 1% are demanded rF. The dampness monitoring is extremely important also with plants for the production of liquid crystal screens and colors. In these cases the durability and accuracy of the dampness sensors plays a large role. Straight ones in such production plants arise often unwanted air pollutants, by which the sensor elements are affected. Sensor technologies for dampness and TaupunktIn of practice are used two kinds by dampness sensors, which measure the water content of air: a type of sensor measures rel. Dampness, the other one the dew point. In an atmosphere with a humidity content of at least 10% rF a direct moisture test is used predominantly, while with low humidity content a dew point measurement is preferred. In special cases this is used in addition, when high moistening. Among the moistening and dew point sensors rank: 1. Psychrometer2. Mechanical Hygrometer3. Lithiumchlorid-Hygrometer4. Widerstandshygrometer5. Capacitive Hygrometer6. Taupunktspiegel-HygrometerDie sensors 1 - 6 is able to measure normal environment-damp. In addition the sensors 5 and 6 are used with the measurement of low dew point temperatures. The principle of the individual technologies becomes below briefly beschrieben.1. The psychrometer is a simple form of a hygrometer, which consists of two thermometers. Thereby the current air temperature drying-thermometer-measures while the damp thermometer is covered with a wet sock. It is cooled by the evaporation by water. Both the evaporation quantity and the evaporative cold developing thereby depend on the humidity. From the difference of the two temperatures assistance is determined by tables and/or computations the water vapour pressure in the ambient air and from this rel. Dampness computes. The procedure becomes frequently in laboratories and in climatic test chambers� eingesetzt.2. With a mechanical hygrometer the dampness assistance of a material is measured and noted, which pulls together and/or expands with changing dampness, like e.g. human hair. This measurement principle is used for many years. The accuracy of the procedure is not particularly hoch.3. The lithium chloride hygrometer works after a measurement principle, which is based on the hygroscopic characteristic to tighten (ability of a substance of water molecules) of lithium chloride. The sensor consists of one with an absorbent fabric coated coil with a bifilaren coil (two isolated wires with moving in opposite directions flowing rivers). The coil is coated with lithium chloride. An alternating current is led by the coil and the lithium chloride solution, which provides for a heating up. During the heating up of the coil, dependent on the water vapour pressure of the ambient air, water from the lithium chloride solution evaporates. The drier the coil becomes, the more highly rises the resistance in the solution, and the current flow by the coil sinks. Thus it comes again to a cooling of the coil. This warming up and cooling reach finally an equilibrium, transferred to the water neither nor� one takes up. The temperature at this point is directly proportional to the dew point of the Umgebungsluft.4. With a resistance hygrometer the circumstance is used that the electrical resistance humidity of a taking up material changes. Special sensors are used for the measurement of the electrical resistance between the electrodes. This kind resistiver sensor is suitable for measurements in series production and becomes particularly within the range of household appliances and consumer goods�� begun. However the measurements of these devices are with very low or very high dampness environments not particularly genau.5. A capacitive hygrometer measures the dampness, as the capacity change of a thin section polymer is used. This type of sensor a sufficient accuracy and is reached in most cases used frequently in the industry. The patented Vaisala HUMICAP� dampness sensors uses this technology. 6. A dew-point mirror hygrometer uses the water condensation with dew point temperature, if air is cooled down, the water vapour contains. A mirror is cooled down, until the dew point of the gas concerned is reached. With the reaching of the condensation condition� changes the light reflected by the reflected surface. Achieves the mirror surface a stable condition, with that� Evaporation and condensation arise at the same time, are the mirror temperature equal to the dew point temperature of the surrounding gas. This type of sensor is used frequently in research institutes.� The sensors most frequently used in pure areas are that� Resistance hygrometer, the capacitive hygrometer (dew point announcement) and the dew-point mirror hygrometer. With the selection of a suitable measuring instrument it is important not to only orient itself at prices and product specifications but should also� Measuring accuracy, expertise of the manufacturer to different areas of application as well as the available service with to be considered. Particularly these factors contribute then also to the successful employment of the devices. Regular and backactionable calibrations are wichtigEs should be always guaranteed that the values indicated by the measuring instruments are reliable and exact. But is one� regular calibration of substantial importance. Typical calibration intervals are specified in table 1. Table 2 shows the example of a traceability chain of stationary moistening and temperature gauges. World-wide all measurements are based on that� International system of units (international system OF unit - SI). With this system it is guaranteed that as everywhere as possible the same sizes are used and measurements with different measuring instruments at different places are comparable. Each offerer of calibration services should be able to prove a valid traceability chain. At least one laboratory reference must have been calibrated in an external laboratory, then for internal calibration used we DIN some cases can a company-owned calibration department be meaningful, if it is e.g. difficult, the measuring instruments to move (calibration locally) or if a large number of measuring instruments is necessary. If a company-owned calibration service is furnished, it is to be created meaningfully an appropriate institution for it. This can consist of a person or a whole department with appropriate line and calibration personnel. A laboratory calibration is to be always preferred to a suburban calibration. In a laboratory the effects of the environment and thus the number of the affecting factors can be crucially minimized. Calibrations in the enterprise are to be examined a fast and simple possibility of measuring instruments, without they must be removed from the process or range. For this kind of the calibration is work-normally necessary as reference. Work-normally a portable or otherwise like suitable measuring instrument can being, which is used for the calibration of the stationary equipment. Work-normal are calibrated in superordinate laboratories. Vaisala has appreciative calibration services for its printing, temperature, dew point and hygrometers. These achievements are offered over the regional service centers. They are available both for devices already installed and together with the supply of new devices. A free calibration manual of Vaisala can be requested under www.vaisala. com/calibrationbook. The book contains useful information approximately to all questions around the topic calibration literature: Arun S. Mujumdar; Handbook OF Industrial Drying (2006) Vaisala Calibration Book (2007)�

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