Moisture is a constantly varying component in the raw materials for many industrial applications and it is becoming more critical to measure and control accurately. Often laboratory tests are seen as being most accurate, but this article will show the limitations of these for real-time control and why online measurement is essential.
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Many industrial processes batch the raw materials by weight and must achieve the correct balance of the dry ingredients to obtain a repeatable product. Any moisture content will cause problems if the weight of the water is not compensated.
An example of this would be 1000 kg of wet material at 10% moisture which contains only 909 kg of the actual dry material with 91 kg of water.
If the real-time process shown in Figure 1 is tested by collecting samples at the three marked points, these would average at 14% moisture, as shown by the upper line.
If the same process is averaged using data from the continuous measurement, this shows the batch is at 12% moisture, a 2% difference from the moisture calculated by the laboratory.
When this is applied to a process, even if the moisture is checked several times during the day, there will still be an unknown level of water due to this sampling error leading to unwanted results in the final product.