1114 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1957 



In contrast, capacitance values for the controls have remained essentially 

 unchanged. 



There has been no substantial increase in the capacitance of the poly- 

 vinyl chloride-insulated conductors although there is some evidence of 

 an upward trend in the data for the coils in the biologically active en- 

 vironment. There was a rise in capacitance of about 15 fifxi between the 

 one and three month period, and a similar rise between the eighth and 

 tenth month. Future measurements should indicate whether any bio- 

 logical attack is occurring. 



8 ' 



I 



tr 



O- — -o GRS TEST 



A, ^ PVC TEST 



• • GRS CONTROL 



A ▲ PVC CONTROL 



GRS INSULATION-10 MILS 

 PVC INSULATI0N-I2 MILS 





u 

 z 

 < 



I- 

 o 



a 



z 

 o 

 u 



lA-^ 



t^ 



:z:;gS--:it::t— T--..><?"t— ■■ 



■yr 





'Vs»' 



'Vj. A 



\. l^-^-^r j^^"" I I I 



4 5 6 7 8 9 



TIME IN TEST IN MONTHS 



)0 



11 



12 



13 



Fig. 7 — Conductance changes resulting from exposure of GR-S (51-92) and 

 Poly(Vinyl Chloride) insulated conductors in sea water and sediment. 



As may be noted from the conductance data for both materials in 

 Fig. 7, the patterns of the curves for the test and control samples are 

 essentially the same. In all cases there has been a slight increase in con- 

 ductance over the 13 month test period. For GR-S it has increased from 

 about 1.5 to 2.0 ^Mmhos and for the polyvinyl chloride from about 0.75 

 to 1.5 MMmhos. 



In a test of this kind the rise in capacitance, such as that which occurs 

 with the GR-S, without any marked corresponding increase in con- 

 ductance suggests that the insulation is being modified by the attack, 

 rather than actually removed as assumed previously. It also suggests 

 that the action is most hkely due to bacteria rather than fungi which 

 might be expected to penetrate the insulation directly to the conductor 

 and so have a more pronounced effect on conductance. When the test is 

 terminated, it is hoped that these insulated conductors can be run 

 through a capacitance and conductance monitor to locate the specific 

 points of deterioration, and to determine the extent and type of attack. 



