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Wire & Cable ASIA – September/October 2007
102
March/April 2012
A new lay length measurement technology has been
developed that allows high speed acquisition of lay length
data. With this technology, lay lengths can be accurately
measured across different machines. This information can
be useful in a number of ways. For instance, each machine
on a production floor could then be adjusted to deliver a
single desired lay value.
The variation around the nominal lay is also an important
factor that contributes to the crosstalk of the completed
cable. We show that effects such as the double twist bow
rotation as well as the pretwist of the single wires are quite
visible in the analysis of pair length variation. In some
cases, even variation caused by the rotation of the payoff
and take up spool can be seen in the pair lay data.
2 Experimentation
This paper is the outcome of a joint effort of Beta
LaserMike and Tyco Electronics to better understand how
to measure lay lengths, and correlate those measured
values to finished cable performance. In order to develop
a better understanding of the measurement capabilities,
initial trials on individual pairs were conducted. After the
pair lay information was gathered, data was gathered at
a cabling line with simultaneous data on multiple pairs.
The measurement technology includes a rapid sample
rate that allows data to be captured at a rate of several
samples per lay length. This rapid sample rate allows the
further processing of the data, such as FFT analysis, trend
analysis, and statistical evaluation.
2.1 Pair lay studies
Initial trials were set up to measure pair lays that used a
rewind line. This arrangement provided a simpler setup
and allowed the measurement of pair lays across a
number of twinning machines. Analysis and experiments
were conducted to evaluate the measurement equipment
performance as well as the differences seen across lay set
points and process equipment.
2.1.1 Nominal lay of individual pairs
An example of the distribution of measured pair lay is
shown in
Figure 1
. The data is in histogram format, with
a probability density that reflects the distribution of the
lay length data over the length of the pair sample. The
x-axis scale has been calculated as a per cent deviation
from the target to normalise the variation and the mean
% Dev Pair 3
❍
❍
Figure 4
: Same lay length produced on two different machines
% Deviation from Target
Pair 3
% Deviation from Target
Pair 3
% Dev Pair 3
❍
❍
Figure 3
: Different process set points for the same lay
length
% Deviation from Target
Pair 1
% Deviation from Target
Pair 1
% Dev Pair 1
% Dev Pair 1
Frequency
Frequency
Frequency
Frequency
❍
❍
Figure 2
: Repeated measurements of replicated trials
Frequency
Frequency
% Deviation from Target
Pair 2
% Dev Pair 2
% Dev Pair 2
% Deviation from Target
Pair 2
% Dev Pair 3