INCREMENTAL SHP:ATH rillCKMOHS MEASUREMENTS 



307 



,^^ 



:/ 



AVERAGE CAPACITANCE VALUES (9FT SECTIONS) 

 OF THE RECORDER GRAPH 



AVERAGE THICKNESS VALUES (OF 18 POINTS) 

 FROM THE MICROMETER MEASUREMENTS 



90 OJ 



Z 



1-80 ^ 



Fig. 9 — Comparison of average values from graphs of P'ig. 8. 



while the micrometer readings are point measurements taken at discrete 

 distances at the bottom of the corrugation valleys in the polyethylene 

 jacket. Despite this fact, the statistical character of both graphical 

 results is closely similar (See Fig. 9). Assuming an average translation 

 factor of 0.005 mmF per 0.001 inch, and discarding tracing errors, the 

 agreement for incremental measurements between both methods can be 

 estimated to be of the order of 0.003 inch. This accuracy is ample for any 

 practical purpose of incremental thickness control of cable sheathing. 



4 CONCLUSIONS 



The method presented here for non-conductive sheath thickness meas- 

 urements yields sufficient stability and translation reliability to be con- 

 sidered an improvement in the art. In particular, the incremental 

 capacitance measurement accuracy of the order of 0.003 miF (equivalent 

 to less than 0.001 of an inch of in("remental sheath thickness) is suffi- 

 cienth' high to disregard, in practical applications, the error of the test 

 set itself. When measuring flat samples in stationary conditions ac- 

 curacies of the order of 0.002" for absolute thickness are obtainable. 



Reliable differential measurements of cable sheathing on the produc- 

 tion line can be realized on a statistical basis. Accuracies of the order of 

 0.003 of an inch for incremental sheath thickness (eccentricity) measure- 

 ments were consistently attained in actual manufacturing conditions. 



Extensive experience with the described measuring system indicates 

 that it can also be applied for absolute sheath thickness measurements 

 ^nelding desirable accuracies. This application, however, involves various 

 manufacturing and process control problems extraneous to the measuring 

 system per se. These aspects, therefore, are not discussed in the prestMit 

 paper. * 



* Development of techniques for al)solute sheath thickness measurements, 

 using the described system, is being conducted by W. T. Eppler of Western Elec- 

 tric Co., Inc., Kearny, N.J. 



