In the determination of water content in food and other products containing 8% - 100% water, the latest solution for moisture analysis is manufactured by Radwag and uses microwave radiation. Absorption of the microwave radiation by polar compounds of the product (mainly water) increases the product temperature.
As a consequence of radiation absorption, molecular friction is caused by the occurrence of the reorientation of dipoles of polar compounds (Al-Harahsheh M, Al-Muhtaseb and Magee 2009).
A fast increase in temperature within the whole product volume is brought about by this. The power and frequency of the emitted microwaves, as well as the product structure and its chemical content, dictate the drying process efficiency (Soysal 2004; Kamińska and Ciesielczyk 2011).
Features of the PMV Microwave Moisture Analyzer
As a modern and productive piece of weighing equipment, PMV microwave moisture analyzer offers:
- Short drying time (maximum of 2 – 5 minutes)
- products, drying programs, completed drying procedures databases
- statistical analysis for water content determination in selected product
- Interactive menu with definable buttons, info fields, permission levels, etc.
- Interactive proximity sensors
- Drying process visualization displayed as a drying curve
- Export / import of products and drying programs databases, remaining data
- Communication via RS 232, USB, Ethernet, Wi-Fi
Figure 1. PMV 50 microwave moisture analyzer. Image Credit: Radwag Balances & Scales
Figure 2 presents a diagram of PMV 50 microwave moisture analyzer manufactured by Radwag Wagi Elektroniczne, Poland, showing the main subassemblies.
Figure 2. Diagram of PMV 50 microwave moisture analyzer. Image Credit: Radwag Balances & Scales
Means of Operation of the Microwave Moisture Analyzer
Electromagnetic system (1), comprising carefully selected monoblock components, is used to carry out measurements of the analyzed product mass. This allows the weighing system to remain stable even when operating in unstable ambient conditions. There is a weighing pan (4) inside the drying chamber (2), which is loaded with a product (6) before being placed between two glass fiber filters (5).
Microwaves are emitted by a magnetron (3) that result from the dipole effect of water molecules in a product (6). This increases the product temperature. An infrared sensor is used to monitor the temperature (7). This is installed in the top part of the drying chamber (2). An individual feature of each product is maximum product temperature. This is one of the drying parameters. The current product’s temperature is registered with the temperature sensor (7) and any information obtained is used by a system controlling the power of the magnetron (3). The analyzed product temperature drops (desorption of water from the product results with lower molecular friction), the emitted microwaves' power changes and its intensity matches dynamics of the process.
Up until the condition of product mass stability over time is met, the product water content is analyzed. The MA 50.X2.A moisture analyzer uses the same approach, which in this case, means complete desorption of water from the product structure.
PMV 50 moisture analyzers are used to determine water content (%M) in the analyzed products, i.e.: natural yogurt, milk, vanilla quark, creamy quark with olives, and margarine. This information is then used in the following equations:
%M – water content (relative humidity)
% D – dry mass content (absolute humidity)
m1 – wet product mass, prior analysis start
m2 – dry product mass, upon analysis completion
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