Overview
Today’s producers of quality grades must meet stringent customer demands for uniform paper, both in the machine-direction (MD) and cross-direction (CD). That’s why accurate measurement and control of basis weight are crucial in meeting end-customer quality specifications.
But operators are left in the dark when a Quality Control System (QCS) goes offline for a sheet break or start-up event. And that means operators can’t ensure paper meets specifications until the scanner is back on the sheet without additional inputs.
What are Virtual Measurements?
Virtual Measurements, also known as soft sensors, are data models generated by machine learning technologies that use key process variable data points to produce inferred calculations of paper properties. By adding an online Virtual Measurement component to traditional monitoring and testing methods, papermakers can get valid data-based estimates of pulp and paper properties – which for various reasons may not always be directly measurable in real-time or with a physical sensor.
DID YOU KNOW?
It is still considered downtime when the machine is running but the sheet is not threaded to the reel. If the paper stays on target, the sheet is easier to rethread, reducing downtime.
Continuous self-correlation for best accuracy
The status of the Virtual Measurement is shown in the block immediately above the trendlines. During normal operation, this box will remain gray and read ‘Normal’. This indicates that the virtual measurement is receiving valid inputs to calculate the inferred weight, and also that a valid scanner measurement of weight is available.
During this normal operation, while the scanner is on-sheet and measuring, the virtual measurement continuously correlates itself to the scanner measurements – to improve accuracy during the critical times when the scanner is unavailable.
If there is a lack of data for the online calculation, or the input signals are invalid, an error message such as “out of range” appears.
When the machine starts up, so do the input signals, and the virtual measurement can pull data to calculate the inferred weight. The status changes to “estimating”, turning a bright blue to draw attention.
This would be an indication that the QCS scanner is offline. It’s also when the Weight Virtual Measurement is most valuable, becoming the stand-in for the now missing physical measurement of weight.
Operators can stabilize weight before scanner is back in action
By leveraging Weight Virtual Measurements before the scanner is back online, the PM operators can take step-change actions, such as manipulating the stock flow, to reach the target weight. This sharply cuts the time needed to get back on spec, reducing the impact and cost of a sheet break.
Weight Virtual Measurement can help you get faster start-ups, lower rejects and improved profitability.
