What is a Virtual Measurement?
Virtual Measurements, also known as soft sensors, are data models generated from machine learning technologies that use various process variable data points to produce inferred calculations of paper property measurements. Adding an online measurement component to traditional paper testing methods provides a data-based estimate of a pulp or paper property that cannot necessarily be measured in real-time or by a physical sensor.
Online measurements should be used in addition to QCS and laboratory measurements for improved quality control. While both traditional online and lab measurement methods provide valuable insight, you do not get online visibility of sheet strength during the papermaking process without incorporating virtual measurements.
How does a Virtual Measurement determine strength?
Better quality control depends on process optimization. Online virtual measurements are created from the combination of available online and/or offline process and product measurements to give visibility into process performance and improvement areas.
First, a strength model is created using historical machine data to establish an initial expectation of the accuracy of the calculated strength. Multiple data modeling steps are followed, including synchronizing data based on time as well as cleaning, filtering, validating and more.
Once the accuracy of an initial model is confirmed, it is implemented for a site-specific online calculated strength measurement based on a mill's paper machine configuration. The virtual measurement calculation is further improved by gaining a better understanding of machine operation, systematic model refinement, and the implementation of measurement suspension events during periods of un-modeled machine operation. Ongoing performance monitoring is done to maintain and optimize the strength calculation.
Variables that impact strength
• Conditioned weight
• Machine speed
• Freeness
• Sheet width
• Rush drag
• Furnish mix
• Refining
• Chemical additions
• Other machine-specific variables
How is the measurement is used for quality control?
With ABB's Strength Virtual Measurement, strength values are provided as frequently as the machine operation requires, up to 1 value every 5 seconds. This is a huge improvement compared to relying on lab measurements, which are only available after reel turnup.
Operators can monitor the trend line to make changes to process or machine variables to keep strength above required specifications.
The horizontal lines indicate the lower reject limits and upper maximum target. The green trend line shows the online strength value.
How is the measurement is used for quality control?
With ABB's Strength Virtual Measurement, strength values are provided as frequently as the machine operation requires, up to 1 value every 5 seconds. This is a huge improvement compared to relying on lab measurements, which are only available after reel turnup.
Operators can monitor the trend line to make changes to process or machine variables to keep strength above required specifications.
Increase strength at no cost
Let’s look at an example where the customer increased strength at no cost by changing the rush drag to optimize the fiber orientation in the paper. A precise sheet fiber orientation square point was achieved, keeping the strength well above target while also enabling the weight target to be reduced.
Operators can monitor both the strength property and individual inputs with each change they make.
Troubleshoot machine issues
The interface also tracks sheet breaks (see the red vertical shaded region in the diagram). Operators will be able to see if the strength is behaving differently before and after a sheet break to troubleshoot potential related issues on the machine.
The red vertical shaded region indicates a sheet break.
Identify trends and improvement opportunities
Engineers and/or management also can view related performance KPIs to understand the stability or change in performance over time of paper strength, such as reject reduction or actual use of the measurement itself.
For example, the orange dots shown here indicate the number of minutes the virtual measurement showed strength below target for a specific shift. Meanwhile, the red dots show the amount of actual rejects during same period. This verifies that during this shift, no action was taken to address strength issues since the number or rejects increased.
With the value of using virtual measurements clearly trackable, operators have the confidence to make adjustments based on measurements.
The orange dots indicate the number of minutes the virtual measurement showed strength below target for a specific shift. The red dots show the amount of actual rejects during same period.
The more frequent and accurate measurements available with Strength Virtual Measurement enables insight into online strength to make more paper at spec at less cost. Contact us today to learn more about the future of quality control.
Source: ABB
