LABORATORY MOISTURE ANALYSIS EQUIPMENT - LIQUIDS AND SOLIDS
PRACTICAL METHODS OF LABORATORY MOISTURE ANALYSIS
1) LOSS ON DRYING- Classic laboratory direct method moisture test for solids and semi-solids, where materials are heated so that moisture present in the material evaporates. The ending weight is subtracted from the beginning weight, and expressed as percentage. Although this method is widely used as the standard in many industrial applications, care has to be taken to prevent chemical changes like carbonization, to the sample.
Further complications arise from the inability to completely dehydrate samples, as well as the unintentional loss of volatiles. However, many of the shortcomings may be accounted for, with a basic understanding of sample drying characteristics.
3) CAPACITANCEResults accurate to as close as .1% +/-in seconds.Free flowing granular sample types, corn, coffee, crumbled cookies, dried fruit. Drying curves may need to be established for each commodity, and programmed by end user or factory. These instruments make up the majority of moisture sensing equipment in the agricultural sector, because of their excellent compatibility with samples like seeds, grains, and feeds. They are fast , accurate, portable and durable, although because they are an indirect method, it is recommended to have a back up reference direct method available as an occasional calibration check.
This Sinar Moisture Spear is used for spot checks of agricultural commodoties. The probe is inserted in to a sack, and gives a reading in about 6 seconds.
SENSORS FOR DIFFERENT SAMPLE TYPES AND ENVIRONMENTS
NIR (Near Infrared) Sensors are popular because the sensor doesn't touch the sample or cause sample degradation. They are used in 0-60% moisture determination applications, in materials where the moisture on the surface is representative of, or at least can be correlated to the moisture throughout the rest of the sample. Multiple sensors can also be used to gather moisture data, at different locations. Environmental temperatures have little effect with applications.
Microwave Sensors read moisture through the entire sample, and is appropriate for most baled moisture-content applications, including cotton, tobacco, and recycled paper.
NIR Inline Continuous Moisture System
RF HIGH TEMP CAPACITANCE TYPE MOISTURE SENSOR
In particular, different heat sources work differently, some having less of an effect on materials prone to volatiles loss and carbonization, than others. The SHIMADZU MOC 120H (THERMOGRAVIMETRICS) Moisture Analyzer utilizes a mid infra-red heat source that helps prevent carbonization and reduces the effects of sample color on heat absorption. PMC SERIES now offers an IR Emitter Bulb, that accomplishes the same thing. Glass fiber pads may also be utilized. Altering the temperature and time parameters of a test will also facilitate accurate testing. At 48 c, degradation reactions are considered to be absent for the majority of known food products. The above files show some different sample types, and the effects of temperature & time changes on their drying characteristics.
For most quality control applications, actual oven tests are not very practical. Results from forced air ovens can differ from vacuum oven test results, and microwave ovens can alter the chemical structure of some products, limiting it' s use. Direct Method Loss on Drying Tests, can be quickly and effectively conducted with the use of moisture balances, commonly referred to as thermogravimetrics, or Infra-Red. These instruments reduce the drying time dramatically, and because they weigh and dry the sample simultaneously, reduce many of the environmental factors that can result in inaccurate results. Care must be taken however, to utilize optimal sample preparation techniques, and optimal time and temperature settings. Many come with software or programs in order to help achieve this.
FLOW SENSOR FOR SINAR DRYPRO INLINE MOISTURE ANALYZER
Typical applications include low level moisture applications for liquids and dispersed solids. The moisture vaporizer add-on can be used to deal with those products that are insoluble and not powdered such as polymeric items e.g. biomedical parts.
Chemicals & Solvents
2) KARL FISCHER- ELECTRO CHEMICAL DIRECT METHOD USED FOR DETERMINING MOISTURE LEVELS IN LIQUIDS, AND DISPERSED SOLIDS
Some of the more commonly used methods to determine the presence of water in raw materials, and finished goods, include: Loss on Drying (Ovens,Thermogravimetrics / Infrared, Microwave) Karl Fischer, Capacitance, (Includes RF Loss of Signal) , X-ray, and NIR.
It should be noted that industries often adopt methods not only based on their ability to provide accurate results, but also on many other factors that may be particular to their specific application, including; ease of implementation, speed, cost, and portability.
This same technology works well for inline sensor contact applications, where the surface moisture may not be representative of the moisture throughout the sample.
The benefit to an inline system, is that it removes some of the labor, and subsequent human error. Also the moisture percentage readings can generally be converted in to a 4-20 ma electronic signal, that can then be directed in to the equipment controls, to help automate the process. For example, the moisture content of a sample moving along a conveyer belt system, through a dryer, can be converted in to a signal that can alter the speed of the conveyer belt, thereby changing the rate, or perhaps even the temperature, at which the product is dried.