Moisture measurement

Moisture measurements are important in the process industries because moisture can foul products, poison reactions, damage equipment, or cause explosions. Moisture measurements include both absolute-moisture methods and relative-humidity methods. The absolute methods are those that provide a primaiy output that can be directly calibrated in terms of dew-point temperature, molar concentration, or weight concentration. Loss of weight on heating is the most familiar of these methods. The relative-humidity methods are those that provide a primaiy output that can be more direc tly calibrated in terms of percentage of saturation of moisture. 

Dew-Point Method For many applications, the dew point is the desired moisture measurement. VHien concentration is desired, the relation between water content and dew point is well-known and available. The dew-point method requires an inert surface whose temperature can be adjusted and measured, a sample gas stream flowing past the surface, a manipulated variable for adjusting the surface temperature to the dew point, and a means of detecting the onset of con-densation. 

Estimating Minimum Sample Quantity for Moisture Measurement Estimates of material quantity for testing moisture content depend on mechanisms of moisture distribution in the material. Moisture is physically retained on particle surfaces, chemically adsorbed on surfaces and within pores of particulate solids, and contained as an internal constituent of solids. Significant internal moisture is most often encountered in organic and agricultural source materials. 

Ref 58 discusses the application of electronic instrumentation to moisture measurement. Procedures amenable to use for energetic materials include ... 

Wexi.ER, A. In Humidity and Moisture. Measurements and Control in Science and Industry. Volume 1 Principles and Methods of Humidity Measurement in Gases, (Ed. R. E. Ruskin) (Reinhold. New York,... 

Meadowcroft, D. B. In Instrumentation Reference Book, (Ed. B. E. Noltingk), Chapter 6. Chemical analysis — moisture measurement (Butterworth, 1988). 

A.Z. David, I. Antal, Z. Acs, L. Gal and D. Greskovits, Investigation of water diffusion in piracetam by microwave moisture measurement and near-infrared spectroscopy, Hung. J. Ind. Chem., 28, 267-270 (2000). 

Figure 23 On-line moisture measurement during fluid bed drying vs. at-line measurement using Computrac . Source. From http //www.brimrose.com/pharmal. html anhor02.

The aluminum oxide sensor is also used for moisture measurements in liquids (hydrocarbons). Because ot us low power usage, it is suitable lor use in explosion prool installations. These sensors are frequently used in petrochemical applications where low dew points are to he monitored on line and where the reduced accuracies and other limitations are acceptable. The advantages of the sensor must be weighted against the fact that... 

Expressible moisture measures the water expressed from a material under a force. Its measurement requires centrifugation of samples on filter paper to remove the released moisture. The filter paper needs to be weighed before and after centrifugation. Weight loss of the sample can also be measured by weighing before and after centrifugation. 

C. P. Wong and D. E. Maurer in Semiconductor Moisture Measurement Technology, Special Publication 400-72, National Bureau of Standards, 1982, p. 275. 

Application to Moisture Measurement with Hydrated Aluminum Oxide Films... 

Senturia, S. D. Huberman, M. G. Van der Eloot, R. Proc. ARPA/fBS Workshop on Moisture Measurement in Integrated Circuit Packages, (1978) MIS Special Publication 400-69, p. 108. 

Rantanen, J. Rasanen, E. Tenhunen, J. etal, In-line moisture measurement during granulation with a four-wavelength near infrared sensor An evaluation of particle size and binder effects Eur. J. Pharm. Biopharm. 2000, 50, 271-276. 

As indicated previously, moisture was measured by oven-drying at 103°C for 24 h (8). Three samples from each of the five silages were taken for moisture measurement. Mean particle length (MPL) was measured by the standard separator method using five screens and a pan (11). Three samples of about 2 kg each were taken to measure MPL for each of the five silages. 

ASAE. (2002), Moisture Measurement—Forages. ASAE S358.2. Standards, 49th Edition. American Society of Agricultural Engineers, St. Joseph, MI. 

---