... from www.positek.com
Modern high speed paper making machines are fantastic, producing
1500m of paper 9m wide per minute. It's a lot of paper moving
very fast. And the quality of the paper produced is superb with
different finishes required for different types of end use.
The paper is produced from pulp which is fed onto a 'tape'
and is then passed through a hot section, running continuously
at over 90°C, which gradually dries the pulp out until it
is strong enough to be handled as a continuous sheet.
The whole process is simple in nature but the machinery is
extremely complex and tightly controlled to ensure the quality
of the paper.The whole machine is huge taking up most of a building
300m long and is over 9m wide and about 15m high.
The machines run continuously 24 hrs a day and stoppages and
breakages are very costly.
Within the machine it is important to control the position
of the tape carrying the drying pulp across the rollers which
are spinning fast. If the tape slides across the rollers it
can be damaged resulting in complete replacement and long stoppages.
The position of the tape is controlled using an optical edge
recognition system combined with a mechanical servo control
of the roller attitude.
At the heart of this edge control system is the Positek P101
Linear Inductive Position Sensor mounted at the end of the roller.The
sensor measures the roller attitude and relays the information
to the control system. The roller is operating in the section
of the machine where the pulp is dried. It is very hot, 90 to
110°C, and the humidity is high in this enclosed section.
The manufacturer of the paper machines needed a sensor which
could withstand this tough environment. Positek were able to
offer a 2 wire 4-20mA output option on the P101 sensors which
would operate over long periods at the high temperatures.
The customer also needed a sensor which was made entirely form
stainless steel so that it would withstand the corrosive and
damp environment. Positek were able to modify the design of
some of the parts so that the sensor would satisfy the requirements
of the customer.
During the early part of the project to develop the sensor
for the application some difficulties were encountered with
some of the mechanical parts, such as bearings, not coping with
the environment over a long period. Positek is committed to
working closely with customers and solving their problems and
these early difficulties were resolved by co-operation between
Positek and the customer. Interestingly the biggest concern
at the start of the project was the ability of the electronic
components to survive the harsh environment but these have performed
very well.
The sensor is supplied by Positek calibrated to within +/-
0.25% of the overall range both for the slope and the offset
of the output. The end face of the body is used as the reference
when it is calibrated. The internally-integrated Positek sensors
permit simplification of the installation of the control system
because the output is a loop powered two-wire 4-20mA format.
The Positek sensor has just 2 connections to make, resulting
in quicker installation.
A further advantage of the LIPS® sensor derives from its
fully linear response over the entire mechanical range. The
sensor provides a linear response to within +/- 0.5% of the
travel.
The P101 sensor incorporates technology developed by Positek
and used in its other displacement sensor products. This PIPS®
technology, is based on inductive coils and uses a unique custom
integrated circuit to produce an accurate analogue output signal.
