Easy In-line Moisture Measurement Without Elaborate Calibration

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DÜPERTHAL Sicherheitstechnik GmbH & Co. KG

Cleaning the observation window before taking a sample increases the accuracy of the calibration and leads to significantly more precise absolute values with 100 percent reliability. In many applications, the determination of moisture content has to be very accurate, better than 0.15 percent, even with moisture contents which can lie below one percent.

Additional Information

Applications

Continuous Quality

The aim of indirect moisture measurement in process guidance or process control is the continuous collecting of moisture readings so that process times can be optimised and a constant (good) product quality achieved. In addition, the precise determination of the product moisture content and the consequent adjustments have a substantial influence on subsequent operational processes and their trouble-free running. The advantages are elucidated here using two examples:

Moisture determination, e.g. fluidised bed and wet granulation:

time saving enables the production of one or more additional batches in the same time

precise moisture residue at drying end point, secure running for subsequent processes

avoidance of follow-up work

rise in quality and, under certain circumstances, avoidance of microbial effects in the product

Moisture determination in continuous processes, e.g. ConsiGma:

problem-free and continuous process running

parameters for installation control every second

constant quality of process and product

The moisture sensor analyses the product moisture content at a frequency of 1 Hz with an accuracy of approximately ±0.12 percent at a residual moisture of one percent. These values, however, can only be achieved if the reference analytics work within a correspondingly small error. At lower levels of product moisture content, the KFT reference method is to be preferred to the LOD reference method, as it can achieve more accurate results. Precise reference values are a precondition, for these allow precise determination of the parameters for the sensor and, consequently, of the online moisture content readings. The accuracy of the calibration is critically dependent on the precisely timed taking of the sample and the simultaneous measurement. For firms which work under GMP conditions, this procedure should be easy to carry out and should not represent a obstacle.

Supplementary Online Measurment – How It's Done

Conclusion: Online measurement of the drying end-point in discontinous processes can be carried out as a supplementary procedure advising when to take the final moisture sample to send for laboratory analysis. While still fulfilling the existing guidelines or the process description the operator is sure to have reached the desired quality and can start discharging without having to wait for the lab analysis which will still be needed to release the batch.

With the moisture sensor, the end of the drying process can be detected exactly and the process concluded according to a pre-arranged plan, perhaps when confidence level in the technology is high enough, the production method can be re-registered with an immediate release of the product bases on the online measurement. Continuous processes benefit from a large number of measurement points. The cleaning of the probe at any desired point during drying enables an immediately available protocol, monitored process guidance and control of product moistness. ●

* The authors are on the staff of GEA Pharma Systems.

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Process Analysis

Easy In-line Moisture Measurement Without Elaborate Calibration

Supplementary Online Measurment – How It's Done