WCA March 2012

High speed laser gauges for lay length measurement and FFT analysis for assessment of process stability By Stephen Pearson, Tyco Electronics, Greensboro and Kenneth E Cornelison, Beta LaserMike, Dayton, OH USA

Abstract In this paper, we describe the work done to evaluate crosstalk performance in Category 5 and higher data communication cables. Specifically, a new technology was introduced that allows the accurate measurement of the lay of pairs. In addition this technology provides information about the variability of the lay along the length of the pair. We show in this paper how the pair lay length as well as the variation of the lay affect the crosstalk performance. Unlike designs that intentionally induce changes in lay length,

% Deviation from Target Pair 1

Frequency

% Dev Pair 1

❍ ❍ Figure 1 : Example of lay length distribution

the effects discovered and described occur as part of the mechanical operation of the pairing and cabling equipment. We have shown that by changing set points on the machines other than the lay setting itself, changes in the crosstalk performance of finished category cable performance occurs. These changes in performance are also accompanied by changes in the lay length values, even with the same lay length set points on the machine. 1 Introduction It is well known in the industry that crosstalk is a key characteristic for high performance category cables. In many instances, manufacturers guarantee crosstalk performance better than industry standards. This high level of performance requires the implementation of a solid product design and stable manufacturing processes. It is also well known that even with a solid design, excessive process variation will reduce crosstalk performance.

Changes in performance may occur quickly in the case of a specific machine or process upset. Changes in performance may also occur slowly over the course of days or weeks that are often caused by gradual changes in the operation of the manufacturing equipment. It is not uncommon to implement scheduled maintenance of equipment to reduce the instances of performance degradation, but the effectiveness of that maintenance to control the lay length attributes has not been understood adequately. Another key factor affecting crosstalk performance is the consistency of lay lengths across a number of different machines. It is known, or at least previously suspected, that the lay length can be different from machine to machine. Managing the use of different machines on a factory floor without good feedback on the actual pair lays is often a problem. This can also be a significant barrier to production scheduling, since often only certain ‘qualified’ equipment can be used on specific products.

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