• April 21, 2024

Moisture content monitoring in FBD refers to the techniques for measuring the quantity of moisture for the material in the Fluid Bed Dryer. The value of the moisture content is used in determining various process parameters such as drying temperature and time. The accurate and effective drying process depends on the quantity of moisture in the material being dried, which depends on the humidity monitoring instruments and techniques.

Moisture content monitoring in FBD

Fluid Bed Dryer is used to dry the material up to the required level to make it compatible with various Pharmaceutical oral solid forms. An essential parameter in the success of a fluid bed dryer is the drying time of the material, which enables it to serve the drug’s therapeutic effect. Moisture monitoring allows us to determine an ideal product characteristic suitable for manufacturing pharmaceutical products.

Some instruments and accessories aid in the success of the dying process, while others are meant for designing the product parameters. Moisture content monitoring is used to optimize process parameters.

Online vs. Offline moisture content monitoring in fbd

There are two types of moisture monitoring for a Fluid Bed Dryer – offline and online.

Online Monitoring

Online moisture monitoring utilizes continuous moisture monitoring during drying. There is no need to stop the process for taking a sample and performing the analysis.


The output of this method is used as feedback to the central controller of the fluid bed dryer, which uses it to adjust operating parameters in real-time, without human intervention. The process parameters are adjusted during machine operation without stopping the operation.

Offline monitoring

Offline monitoring refers to the traditional method of taking a sample from the machine to the lab for measuring moisture content. For sample collection, the process is stopped, and a sample is taken, usually through a sampling port. The process remains stopped during sampling and until results are finalized.

The drying operation depends on the moisture measurement results for adjusting and optimizing. The equipment remains stopped until results are finalized, and parameters are incorporated into the equipment.

Offline moisture measurement is usually time-consuming and is prone to various errors such as human, environmental and handling errors.

This method consumes more time in finalizing and implementing results in the fluid bed dryer. The offline mode also consumes more time, adjusting and optimizing the process parameters because it is a trial-and-error method.

Importance of moisture content monitoring in FBD


  • The main aim of measuring moisture content is to have optimum material drying. It is used to prevent over or under-drying of material, enabling it to provide desired product characteristics for the therapeutic requirement.


  • Measuring moisture content also helps optimize production process parameters such as drying time and temperature. It helps in setting up a parameter that best provides the product specification.


Methods of measuring moisture content monitoring in FBD


Let’s discuss common ways to determine moisture content in fluid bed drying.


Product temperature


The temperature of the product can be monitored to determine the moisture content. A temperature sensor is installed in the product container, which measures the product temperature.

Before drying, the product temperature is low because it contains moisture. During drying, hot air passes through the product, removes the moisture from it, and decreases the moisture content.

As the quantity of moisture decreases, the product temperature increases. Product temperature for the required moisture content is pre-developed through appropriate studies in the product research and development stage.

Near-infrared spectroscopy – NIR

Near-infrared spectroscopy determines the moisture content by analyzing the reflection of electromagnetic radiation from the product particles.

The radiation lies in the range of 700 to 250 nm. Different quantities of moisture in the sample will result in different light scattering values. Similarly, the value of NIR is determined for reduced and ideal moisture levels.

The NIR spectroscopy is a real-time monitoring technique that can perform moisture measurements without sample preparation. This technique is also part of Process Analytical Technology – PAT in the continuous manufacturing processes.

Moisture Analyzer

A moisture analyzer is an analytical method used in laboratories to measure moisture content. For measurement, the sample is taken from the FBD through a sampling port and is sent to the lab, where it is placed in an instrument called a moisture analyzer

It works on the principle of Loss of Drying. According to this principle, the sample is the first weight to determine its total weight of the sample. Then the sample is dried until no further loss in moisture r is observed. The difference between the weight of the dried sample and the un-dried sample is considered a loss in moisture, and the instrument determines the relevant humidity of the sample.

The entire process i.e. weighing, drying and result compilation, is automated without the involvement of humans.


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