Meaning
Mathematical corrections applied during coulometric titration isolate the actual water content of a sample from moisture entering the system from the environment. Through background drift subtraction, the analyzer measures the rate of ambient moisture ingress before the test starts and deducts this value from the total measured water. This correction is essential for low-level moisture analysis where ambient humidity could otherwise dwarf the sample signal.
Correction Algorithm
The analyzer continuously monitors the moisture level in the titration cell during idle periods, establishing a baseline drift rate in micrograms of water per minute. When a polymer sample is introduced, the instrument calculates the total moisture detected and subtracts the product of the drift rate and the test duration. This process prevents the ambient humidity that sneaks past the cell seals from skewing the final result.
Accurate subtraction is particularly critical when analyzing hygroscopic materials like polyamide where small moisture variations affect processing behavior.
Moulding Relevance
Injection moulders rely on precise moisture measurements to set up drying schedules and prevent polymer hydrolysis during processing. An incorrect subtraction that underestimates moisture might cause resin to be processed while still too wet, resulting in part brittleness and bubbles. Correct subtraction prevents these errors by ensuring that the dry resin meets the strict processing limits required for structural integrity.
System Integrity
High baseline drift values often indicate worn septa and poor cell assembly. Even with subtraction algorithms, excessively high drift introduces statistical noise into the final moisture calculation. Regularly replacing seals maintains low starting drift values, which improves the reproducibility of moisture tests across multiple shifts.
