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Feature Article in PE&M February 1999

Following is the text of the feature as it appeared in "Paper Equipment & Materials International" magazine.

January 10, 1999

MultiPerm gives total porosity control (January, 1999, Vol.8 No. 1)

 The MultiPerm™ on‑line porosity measurement system from Value Systems in the UK provides a correlation of ±3% with the quality control laboratory. It is a new system designed and manufactured in the UK by Value Systems since 1993. There are now over 30 systems installed worldwide and as the measurement cycle has been improved and speeded up the system has become recognized as a market leader. Its present position has been achieved through the advanced sensor technology providing on‑line measurement accuracy not previously attainable.

The MultiPerm system scans the measurement cycle to achieve a sampling frequency every 2.5 cm of the paper web in the machine direction. This equates to 400 Hertz at 600 m/min and 800 Hertz at 1200 m/min. These rapid measurements result in high measurement accuracy and statistical analysis of the complete parent reel as it builds on the paper machine pope reel. In this way, the operator has a constant update of the web as it develops rather than as a post production sample taken at the end of a reel once it has been wound and removed from the wind‑up.

 This is important when a product is sold, based on reel 'Coefficient of Variance' (CoV) statistics, as is generally the case with cigarette tissue grades. It is easier to make 'A' grade paper if a continuous and accurate statistical analysis is available as the product is being manufactured. The system also allows the recall of reports on every reel produced on that particular PM.

 Confirmation of the effectiveness of the equipment was given to PE&M in January this year, by a paper manufacturer in North America who produces a variety of grades particularly sensitive to porosity parameters. 'We have tied the MultiPerm equipment into a full feed­back automated control loop on the paper machine. It has now been running on our machine in this way for about four months and we are particularly pleased with how the PM has become so much more stable. This is before we take into consideration the energy savings offered by running the system, or any out of specification production that may result in a rejected parent reel.

 'We did, originally, make our own system which was a pain to get working and was only operative for 60‑70% of the time. When John Marshall introduced us to MultiPerm what he offered was a much better deal than either we or his competitors could manage and we were very skeptical. Now that the system has been operating successfully for a number of months, it has delivered everything claimed for it and has been operative between 98‑99% of the time. We have only had one slight blip when a small electronic component failed. Having identified the problem over the phone, Value Systems dispatched a replacement immediately and we were able to install it in just a few minutes. I cannot actually think of anything negative to say about it. The mill's technical manager told PEM: 'One of the interesting features is that our operators are always suspicious of a new 'bit of kit' that claims great benefits. Ours now use the MultiPerm as a matter of course and would not be without it.'

Analogue porosity systems have been sold over the past 20‑30 years. Some were not able to withstand the rigours and stringent requirements imposed by the paper industry and have been discarded. Others failed to maintain operator confidence due to calibration and reliability issues leaving mill managers wary of claims that 'All problems have now been resolved in our latest model. A major supplier of scanning systems (QCS) to the paper industry sold off its on‑line porosity system in the early 1990s. Generally, these systems infer porosity measurements based on a series of assumptions and mathematical models.

 MultiPerm has often been selected to replace these systems, for example at Arjo Wiggins Carbonless, in Dartford UK, mostly in mills where production is of high value added grades. General manager and founder of Value Systems, John Marshall said 'Production lines where there is a need for fast measurement feedback is a pre‑requisite to achieving optimum quality control of the final product. These grades include paper, tissue, glass fibre and non­wovens, as well as felts, fabric and technical grade machines. Intelligence provided by the MultiPerm system means it can detect sheet contact with the sensor in case of sheet flap or vibration or if there is a crease or hole. Like the technician in the quality control laboratory, it throws bad readings away. 'At a grammage change one tears out a sample and sends it to the laboratory and if the sample is partially creased the technician will make his measurements on a good area, ignoring the creasing. The MultiPerm system automatically logs these flaws as well. It is very easy to verify sensor accuracy with the QC laboratory because the high on‑line sampling frequency allows the comparison of exactly the same sample.'

 Value Systems offers a performance guarantee of ±3% with the QC laboratory.

 Most mills close the loop immediately after commissioning the system ‑ controlling factors such as refiners, stock flows and fillers. Demand for the system has continued into early 1999 as the high return on investment in it grows. Payback is typically measured in weeks rather than months or years. Every installation has resulted in an increase in average porosity and a decrease in porosity spread.

Immediate benefits of a freer sheet include improved runnability, reduced draw between sections and fewer sheet breaks. Porosity related losses at grade change are generally eliminated.

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Last modified: December 09, 2006