3.1.2. Advantages,
Shortcomings
This method has been used for decades.
The system is extremely simple and reliable. It however presents
a disadvantage, namely that the measured values lack predictive
power. They cannot be used for computing the eccentricity but
only the averaged wall thickness in the plane of measurement.
3.1.3. Example
USYS 2000 Processor, Configured
for wall thickess measurement |
3.2. Inductive (Eddy Currents) Technology
3.2.1. Method
This measurement method is based on
an electromagnetic sensor rotating around the cable. The wall
thickness is continuously measured according to a helicoidal
trajectory.
Measuring method |
3.2.2. Measuring Location
The location of the sensor unit must
be such that the cable to be measured is cool enough. This
prevents damage of the cable due to contact with the guide
and the measuring head. As an approximate value, there should
be at least a 10 m cooling bath between the extruder and the
sensor unit.
3.2.3. Advantages
- The measured values are stable
The system provides very stable measured values independently
of the temperature.
- High speed
A speed of up to 2000 m/min can be reached.
- Control of minimal wall thickness
With a combination of Laser- and Inductive Technology automatic
min. wall thickness control is possible1).
(Independent of the eccentricity)
3.2.4. Shortcomings
The relatively long distance due to
the position of the sensor after the cooling bath makes the
control loop rather slow. Contact with the surface cannot
be avoided.
1)
Independent of the eccentricity
|
