Moisture Measurement

Overbelt Microwave Analyser for Moisture Measurement

07/18/2013 | Editor: Marcel Dröttboom

Typical fields of applications of Berthold Technologies' Micro-Polar moisture analyser are to be found in the mining industry and power plants, in the chemical, pulp and paper and building materials industries.
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Typical fields of applications of Berthold Technologies' Micro-Polar moisture analyser are to be found in the mining industry and power plants, in the chemical, pulp and paper and building materials industries. (Picture: Berthold Technologies)

The Micro-Polar by Berthold Technologies is the company's latest online moisture analyser, using state-of-the-art microwave transmission technology. The measurement is carried out non-contacting, either on a conveyor belt or chute.

Without contact to the measured material, the sensors are not subjected to wear and tear and even maintenance is not required at any time. Typical fields of applications are to be found in the mining industry and power plants, in the chemical, pulp and paper and building materials industries. The microwave method is limited for highly conductive materials. However, the company's application experts will evaluate the applicability of the Micro-Polar system for each individual case.

Measuring Principle

The representative microwave transmission technology, penetrating the whole material cross-section, allows for the high accuracy and reliability of the system. Microwaves penetrate the bulk material, causing a rotation of the free water molecules. As a result the velocity of the microwaves is slowed down (phase shift) and their intensity is weakened (attenuation). Both effects are measured and used as a direct indication of the moisture content.

These measuring effects are already achieved by using very small microwave transmission power – typically 0.1 mW. Consequently the measured material is neither warmed nor modified. Factors such as colour, viscosity, inhomogeneous composition or dust have no or only a negligible effect on the measurement performance.

According to Berthold Technologies, the benefits of the system are:

  • non-contacting and non-intrusive,
  • no wear and tear,
  • online process control,
  • measurement of both: phase shift and attenuation,
  • precise and maintenance-free operation,
  • measurement of the whole material profile, and
  • easy to install on existing conveyors or chutes.
  • The measurement is performed with a number of different frequencies per measurement cycle, leading to a very stable and reliable measurement, unaffected by reflexes or resonances. The high dynamic range of Micro-Polar allows the precise determination of moisture on even very high bulk loads. If the bulk height varies, a separate distance sensor can be connected, ensuring highly accurate measuring results.

    Varying particle sizes can affect the measurement performance. Using the radiometric area weight compensation the fluctuating bulk density is reliable compensated and optimum measuring accuracy is achieved. An integrated reference line makes the measurement independent from potential environmental influences.

    The calibration is done directly on the evaluation unit. The software contains a sample taking feature, where laboratory values can be easily entered and linked to the corresponding measurement values. The calibration curve is calculated automatically.

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