Discrepancies in High Yield Pulp Mass Balance Calculations across Multi Ply Board Mills
High yield pulp mass balances fail when mills exclude white water solubles and moisture variation, exposing buyers to chain of custody audit liabilities.
Consistency Transmitter Drift
Sensor Output Deviation
Automated stock preparation requires continuous measurements of the solid-to-liquid ratio in pulp suspensions. The progressive deviation of a sensor’s readings from the true value over time is known as consistency transmitter drift. This occurs due to mechanical wear or chemical build-up within the process stream.
Process Impact Assessment
Variations in the fibre slurry density directly affect the basis weight, thickness and strength properties of the finished paper sheet. When consistency transmitter drift remains undetected, the control system adjusts dilution valves based on erroneous feedback, causing the actual fibre flow to fluctuate. This error can result in light or heavy paper runs that fail to meet quality standards.
In a typical packaging line, a deviation of even one-tenth of a percent in consistency can alter the board stiffness and disrupt the subsequent box converting run.
Maintenance Verification Loop
Regular gravimetric sampling of the pulp stock provides the necessary reference data to identify and correct any sensor inaccuracy. Technicians draw manual samples, dry them in a laboratory oven and calculate the absolute dry content to compare with the live sensor signals. This manual procedure reveals the onset of consistency transmitter drift before it can destabilize the stock preparation loop.
When drift is detected, the transmitter’s internal offset curves are adjusted to realign the electronic output with the physical measurements. Mechanical cleaning of the sensor face during planned shutdowns also minimizes the build-up of pitch or fibers that causes these deviations.