562 THE BELL SYSTEM TECHNICAL JOUKNAL, MAY 1954 



tube and die assembled in extruder head and die adjusting 



in capacitance. The capacitance response is in turn calibrated in thou- 

 sandths of an inch of sheath thickness. The electronic system of the set 

 has been described in the Bell System Technical Journal previously.* It 

 is practical from test set measurements to control the concentricity of 

 Alpeth cable to within 35 per cent and Stalpeth to within 20 per cent. 

 Average thicknesses within ±0.005 inch are maintained. 



Formerly, the safe practice was to use an excess of approximately 10 

 per cent over specified average in order to keep the thin side of eccentric 

 sheath ^\'ithin the minimum spot limit. Control from test set measure- 

 ments eliminated the necessity of using an excess of polyethylene because 

 sheath of improved concentricity maintained close to the specified av- 

 erage thickness does not vary below the specified minimum spot thick- 

 ness. The quality of the sheath is improved because it is of consistently 

 high dimensional unifonnity not previously obtainable. Also, concentric 

 sheath has better flexing characteristics since eccentric sheath concen- 

 trates the stresses of flexing in the thin side. 



* Continuous Incremental Thickness Measurements of Non-Conductive Cable 

 Sheath, B. M. Wojciechowski, B.S.T.J., 33, pp. 353-368, Mar., 1954. 



