Sensor handles high-temperature paper application

Edited by the Engineeringtalk editorial team Sep 25, 2007

A PIPS sensor, based on simple inductive coils using Positek's ASIC control technology, directly measures absolute position giving a DC analogue output signal.

Today's high-speed papermaking machines are capable of producing 1500m of paper, 9m wide per minute at very high quality and in varying finishes for different types of end uses.

The paper is produced from pulp that is fed onto a tape, and then passed through a hot drying section that runs continuously at over 90C to gradually dry the pulp until it is strong enough to be handled as a continuous sheet.

While the process is simple in nature, the machinery is extremely complex and tightly controlled to ensure the paper quality.

And the machinery is huge, taking up most of a building at 300m long and over 9m wide and about 15m high.

Because machines run continuously, 24 hours a day, stoppages and breakages are very costly.

During machine operations, 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 tape replacement and long machine stoppages and downtime.

The position of the tape is controlled using an optical edge recognition system, combined with a mechanical servo control of the roller attitude.

This edge control system uses a linear inductive position sensor to measure the roller attitude and relays the information to the control system.

The roller operates in the section of the machine where the pulp is dried.

It is very hot, up to 90 to 110C, and humidity is high within this enclosed section.

A manufacturer of paper machines needed a sensor that could withstand this tough environment, and the Positek P101 sensor was chosen based on its proven operation in high-temperatures for long periods.

As the customer needed a sensor constructed from stainless steel so to withstand the corrosive and damp environment, Positek modified the design of some of the parts so that the sensor would satisfy the requirements of the customer.

The sensor is very robust, with the body and push rod made of stainless steel for long service life and environmental resistance.

Positek's PIPS technology (Positek inductive position sensors) also helps to eliminate wear.

PIPS-based displacement transducers have the simplicity of a potentiometer with the life of a LVDT.

A PIPS sensor, based on simple inductive coils using Positek's ASIC control technology, directly measures absolute position giving a DC analogue output signal.

Because there is no contact between moving electrical components, reliability is high and wear is eliminated.

The sensor also offers a fully linear response over its entire mechanical range.

The linear inductive position sensor was 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.

Units were offered with a two-wire, 4-20mA output for easy installation into the control system.

With just two connections to make, the Positek sensor resulted in a quicker installation.

The biggest concern at the start of the project was the ability of the sensors' electronic components to survive the harsh environment, but these have performed very well over time.