The Moisture Analyzer; Oven over a Computerized Scale
The industrial scale is accurate enough to satisfy most production control applications where the end item moisture content tolerance is +/- 1.0% or higher, provided the oven is suitable for the determination, and the required measurement software is either present in the scale or can be used externally. Even at this level the ability to upload the weight and temperature information, on a real time basis, to an external process control system can be very important in producing a consistent product.
The precision or laboratory scale is usually not just more accurate but also adds a number of features that make more complicated evaluations a simpler process. Things like programmable heating profiles and statistical analysis during the process can be very useful in some applications. Generally speaking these more expensive analyzers have better and more sophisticated ovens over them. Their temperature sensors may be better and better placed to more truly reflect the sample temperature. The heating may be more evenly distributed so the entire sample tends to be at a more uniform temperature. Some ovens are designed to hold larger samples which can help if uniformity of samples is a problem.
Not all ovens heat in the same way. Most modern moisture analyzers, designed for general purpose uses, are based upon Halogen lamps as heating elements. These devices heat very rapidly and provide a great deal of radiant energy. This can pose a problem in that the sample may heat much more rapidly internally than is reflected by its surface temperature. Some samples may develop a crust that prevents internal heating and thus distorts results. Dowel rod type heaters are slow to heat and provide almost entirely IR type of heat. The user must understand the material characteristics of the sample being tested and arrange for a suitable heating profile.
The oven will invariably require cleaning. The frequency of cleaning is largely determined by the characteristics of the samples and the heating profiles used. Oven designs vary quite widely and it pays to investigate the oven construction and how easy it is to clean and maintain. Changing halogen lamps can be exciting if the mounting is awkward. In all cases be extremely careful not to perform these actions without unplugging the Analyzer. Good analyzers usually have a glass window that prevents spattering from reaching the lamps. But as the glass gets dirty it prevents the lamp radiation from reaching the sample. Cleaning a flat glass pane is easier than cleaning the Halogen lamps and their associated reflectors.
The scale will also require cleaning if the spattering gets on the weigh pan. Almost all modern scales have stainless steel weigh pans, usually designed specially for the moisture analyzer function.
The oven and the software really set the individual offerings apart. Time spent thinking about the characteristics of the samples you are likely to test will go a long way in guiding you to a proper selection of a moisture analyzer.