Final quality control of the goods for actual moisture content
Quality complaints present an undesirable and unpredictable risk of additional effort and costs for both the customer and the producer, therefore it is fundamentally essential to inspect product thoroughly.
It is fundamentally essential to inspect the produced goods for their assured properties such as haptics, dimensional stability, exact net weight, and more before shipping them to the customer. This is to prevent justified complaints regarding the quality of the goods. Quality complaints present an undesirable and unpredictable risk of additional effort and costs for both the customer and the producer. Moreover, they can harm a good customer relationship, which must be avoided at all costs.
As the following reports explain, the moisture content of differentiated products can significantly impact product quality.
1. Moisture measurement after bagging of hygroscopic substances.
In this application, the requirement was to precisely measure the moisture content of a hygroscopic granulate after the bagging process, through the closed plastic, textile fibers, or paper sack—essentially, sack by sack. If the moisture content of the hygroscopic granulate is too high, its ability to absorb different liquids to the maximum decreases. Moreover, this can also serve as an indication to optimize the granulate’s drying process to ensure that the guaranteed net dry weight is filled into the designated containers.
A dielectric microwave sensor is used to perform the moisture measurement. This moisture probe can penetrate the plastic bag to a depth of approximately 50 mm (depending on the material properties) and measure the moisture content within the granulate. The sensor is mounted above the conveyor belt where the sacks are packaged, as shown in Image 1. A pneumatic cylinder presses the probe onto the surface with constant pressure when a certain position is reached, allowing it to measure the moisture content of the granulate through the bag.
Afterward, the probe returns to its waiting position or bell, where it can be pneumatically blown off if needed. For different materials in terms of shape and grain size, any number of calibrations can be stored. The individual measurements can be sent to a processor or PLC unit via an analog or Wi-Fi signal.
The entire moisture profile can be logged via a CSV file that can be imported into Excel. This tool enables simple and efficient quality and error management.
2. Moisture measurement of wooden beams in the sawmill.
When wooden beams are used as structural elements or in visible areas, dimensional stability and shape are crucial. Unnecessary rework on-site or the inability to use twisted or warped beams should be avoided due to the loss of value. Therefore, it is essential to know the natural or storage-induced moisture content of the wood.
Moisture detection can be performed manually using capacitive insertion sensors at specific points, but this process is time-consuming, does not allow for continuous online monitoring, and damages the wood at the insertion points. The requirement was to guide the raw beams on a conveyor roller track after planing, ensuring constant and even contact with the moisture sensor.
In this approach, two pneumatic cylinders press the sliding carriage, which is equipped with an integrated microwave moisture sensor, onto the surface of the beam. This setup allows the beam to be transported smoothly under the measuring device while maintaining contact with the sensor. Additional inductive proximity switches optimize the measuring device by controlling the ideal timing for actuating the pneumatic cylinders.
This method ensures proper contact of the sensor with each wooden beam, piece by piece, in seconds, as shown in Image 2. The obtained measurement data is recorded by a Siemens PLC and documented, as shown in Image 3. It is also determined whether beams with excessively high moisture content need to be sorted out for an additional drying process.
This type of quality control ensures in a large timber company/sawmill, that the products are delivered to the customer within the specified moisture range, saving unnecessary returns and, therefore, costs and inconvenience on-site.
3. Moisture measurement of food or feed before or after the drying process.
In this installation of the moisture measurement probe (see Image 4), the focus was less on optimizing the control and regulation of energy for intensive drying processes—although this is fundamentally possible with the output signals from the moisture probe—and more on continuous online quality control with digital logging of measurement values.
The measured data is transmitted wirelessly to a suitable quality control (QC) system. The custom-developed software assigns the moisture values to the currently measured product. Additionally, the software specifies the intervals and duration for which a measurement is to be carried out and logged.
If the moisture content falls below the permissible level, there is a risk that, for example, pasta will easily break into smaller pieces, which constitutes a visual defect among other issues. If the product moisture is too high, this inevitably leads to mold formation in a sealed package, posing a health risk to consumers.
This approach can be applied not only to food production but also in the feed industry. Continuous moisture quality control can eliminate some of the operator’s need for sporadic manual checks. It also allows for a more relaxed approach to external controls within the framework of a QC inspection.
Close collaboration
It is important to mention that on-site personnel are crucial for the successful implementation of such projects. The close collaboration between system suppliers, the dedicated on-site personnel, and, consequently, the customer as the plant operator, is the key to successfully implementing a functioning online moisture quality control system.
