roLVKTHYLKNK CABLK SIIKATII IIIICKNESS 577 



The location of the four major thickness limits have been indicated 

 below the test graphs. 



CONCLUSIONS 



This test equipment lias proved to be a practical means for the control 

 of the concentricity and the average thickness of the polyethylene sheath 

 on Alpeth and Stalpeth cables. It is accurate, reliable and of rigid con- 

 struction suitable for continuous shop use. It measures the sheath wall 

 thickness directly in thousandths of an inch both visually and as a re- 

 corded graph and does so non-destructively as the sheath is applied. 



Concentricity is maintained within 35 per cent on Alpeth and within 

 20 per cent on Stalpeth cable. Average thickness is controlled to within 

 ±0.005 inch of specified average thickness by the practice of visually 

 averaghig graphs of about twenty-five feet of cable length. 



Polyethj'lene is conserved in two ways which reduce manufacturing 

 costs. First, improved control pemaits operating at specified average 

 thickness \\'ithout varying below minimum spot limit. Previously, an 

 excess over specified average thickness was necessary to prevent the 

 wider range of variation from going below the specified minimum spot 

 thickness. Second, the sheath is of consistently unifoiTn dimensional 

 ciuality not previously obtainable which made it practical to reduce the 

 average wall thickness 11 per cent below previously specified thickness. 



ACKNOWLEDGMENT 



The writer wishes to express his appreciation of the co-operation of 

 B. M. Wojciechowski of the Western Electric Company, who designed 

 the capacitance test set and of Bell Telephone Laboratories cable en- 

 gineers, in establishing the sheath requirements and for their encourage- 

 ment in this project. 



