Responding to last week's column, "Fantastic Voyage"
Stowe Woodward developed and patented fiber optic SMART Technology nip monitoring systems in the late 1990’s and installed more than 20 1st generation rolls in paper mill applications. These systems measured both nip pressure and internal cover temperature in real time.
Fiber optic systems require temperature readings at each sensor because the sensor output changes with any minor temperature variance. Therefore, a correction to the sensor output must be made based on sensor temperature and the system must be calibrated to show accurate results. From our experience over the first few years of using fiber optic sensors, we learned that the temperature readings add no real value to the customer. The roll cover is an insulator so the surface temperature affecting the customer’s operation is not represented by the sensor temperatures. In addition, any increase in internal cover temperature is caused by an increase in load, which is already measured and can provide a more timely warning to prevent cover failure. Today, the SMART covers provided by Stowe Woodward utilize very stable low hysteresis covers that do not generate a significant temperature increase with load. In most cases, the cover’s integrity will be in danger from nip pressure long before a temperature increase is measured.
After utilizing fiber optic systems for several years, Stowe Woodward discontinued this approach and redeveloped and patented SMART Technology using the latest electronics developments. Today, the latest commercially available technology to measure real time nip conditions is Stowe Woodward’s SMART 4.0 technology. The SMART 4.0 electronic sensors measure pressure directly and do not need a correction for temperature variations. Stowe Woodward has shipped more than 230 SMART rolls with the current electronic sensor design. SMART 4.0 systems are running in forming, pressing, size press, breaker stack, coater and calender applications. SMART 4.0 systems are operating in single and multiple nip rolls from the super low lumpbreaker pressures to the super high pressures of the supercalender. SMART 4.0 is running in all paper grades including high speed tissue machines and has provided many millions of dollars in documented savings to our customers.
The next generation of SMART Technology is currently in field trials. SMART 5.0 measures nip width as well as nip pressure and calculates the actual nip impulse curve for optimum paper machine efficiency and paper quality. Roll crown corrections are automatically calculated for the operator. In addition, like the previous SMART Technology versions, SMART 5.0 provides a sensor reading standard deviation output, which can be used by the operator to monitor machine direction variability caused by basis weight variations, machine vibration or other problems.
Director SMART Technology
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