CA1064109A - Method and apparatus for measuring the filling effectiveness of a cable during filling - Google Patents

Abstract

Abstract of the Disclosure The invention relates to the monitoring of the filling effectiveness during the filling operation of a waterproof or filled telecommunications cable on a manufacturing line, and includes measuring the capacitance change per unit length of an outer pair of insulated conductors in the cable, measuring the capacitance change per unit length of an inner pair of insulated conductors in the cable, determining any deviation is the measured capacitance changes and utilizing such deviations by feedback control to eliminate further deviation, as well as determining the point of deviation along the cable length.

Description

This invention relates to method and apparatus for measuring the filling effectiveness of the filling operation in the manufacture of waterproof cables, wherein the capacitance between an outer pair of conductors is measured and the capacitance between an inner pair of conductors is measured, and the capacitances are compared.
Description of the Prior Art Telecommunications cables, especially those that are to be buried in the ground, are desirably moisture proofed to prevent transmission difficulties resulting from the seepage of moisture into the cable. In general, such moisture proofing is accomplished during manufacture of the cable by filling the internal volume of the cable with a suitable filling compound, such as, for example, petrolatum or a mixture of petrolatum and polyethylene.
For the desired results to be achieved, the filling material should preferably occupy substantially all of the volume of the cable that is unoccupied by the conductors and other components therein, including the interstices between twisted pairs of conductors. Various methods and apparatus for filling cables are known, for example, from U.S. Patents Nos. 3,832,215, 3,854,444 and 3,850,139, which issued to Edward L. Franke, et al on 27 August, 17 December and 26 November 1974, respectively; 3,789,099 and 3,876,487, which issued to Carl Eugene Garrett, et al on 29 January 1974 and 8 April 1975, respectively; and 3,733,225, which issued to Larry D. Moody on 15 May 1973.

, , . . .
, . ,: ' ' ll i 1064109 J. A. Eludson et al. 4-2-2 l . .
The normal filling procedure involves the

2 il introduction of the filling compound after the core has been

3 ,I formed and before the final binder and sheath are placed on

4 ¦I the core. At this stage of manufacture, the core is ¦ relatively compact and it is difficult to introduce the 6 ! filling compound, yet the prevention of the ingress of 7 moisture in subsequent use requires t~at ~here be a high 8 percentage of fill in the total fillable volume, preferably 9 evenly distributed throughout the cable cross-section.
Numerous arrangements for ascertaining the 11 amount or percentage of fill material in a cable, which is 12 - an indication of filling operation effectiveness, have been 13 devised. One such arrangement comprises cutting off an end 14 ~ portion of a finished cable and subjecting one end ~hereof ~ water under a known pressure. If more than a 1~ predetermined amount of water flows out of the other end, 17 the cable is unacceptable. Another arrangement comprises 1~ weighing a short length of filled cable. Since the unfilled 19 I weight is known, and the weight of the proper amount of fill 20 1 material for such a length can be determined, the weight of 21 ~ the filled length of cable should at least equal the sum of 22 ¦ the two to be acceptable.
23 ll Still another method for determining the 24 1~ acceptability of the filled cable comprises measurin~ the 25 1I capacitance of a number of pairs of outer conductors in a 26 finished cable, then measuring the capacitance of a number ~7 1 of pairs of inner conductors, and comparing the two 28 measurements. The difference between the two measurements, 29 , divided by the outer measurement provide~ a measure of the 3 filling effectiveness which can then be compared to , I
, !

' 2 "

`` ` 1064109 empirically predetermined values to ascertain whether or not the cable is acceptable.
In the prior art methods of determining filling effectiveness, examples of which are given in the foregoing, the operations are performed on a finished cable, hence if the filling effectiveness is found to be inadequate, a whole cable run must be scrapped or attempts made to refill the cable. In those processes where the measurements or tests are made on a short length of cable, there is no way of determining whether the remainder of the cable is the same as the tested sample, hence a calculated risk is taken in depending on the test results.
In those arrangements where the entire cable length is tested, as in the capacitance measuring method, an indication of non-acceptability may result from only a very short faulty length of cable, which could be cut out if its location along the cable length were known.
This latter problem is common to virtually all of the prior art arrangements, namely, there is no way of ascertaining where, along the cable length, the amount of fill has fallen below an acceptable minimum. An additional -drawback of prior art testing methods is that they are performed on finished cables, and unacceptable cables must be scrapped or refilled, which entails both extra time and money.
Summary of the Invention In accordance with one aspect of the present invention there is provided a method of monitoring the amount of fill being placed in a cable as the cable is advanced through a filling chamber, which comprises the steps of continuously monitoring the changing capacitance of a ~ .

-~ ~ - 3 -.
twisted pair of conductors in the cable, and comparing the monitored changes in capacitance to a predetermined standard value of capacitance change.
In accordance with another aspect of the present invention there is provided apparatus for measuring the filling effectiveness of the filling operation in the manufacture of waterproof cables having a plurality of conductors comprising: first means for continuously measuring the change in capacitance of an outer pair of conductors in the cable as it passes through a filling chamber, second means for continuously measuring the change in capacitance of an inner pair of conductors in the cable as it passes through said filling chamber, and means associated with said first and second means for generating signals indicative of the changes in capacitance of the conductors as the changes occur.
The foregoing problems are overcome by the method and apparatus of the present invention, wherein the method includes the steps of continuously monitoring the change in capacitance of an outer pair of conductors as the cable passes through the filling stage; continuously - 3a -~v~

~ 1064109 J. A. Hudson et al. 4-2-2 monitoring the change in capacitance of an inner pair of conductors as the cable passes through the filling stage;
3 comparing the monitored changes in capacitance with each 4 o~her to ascertain the filling effectiveness of the filling operation; and providing an indication of the location along 6 the cable length of points or regions where deviations in 7 1 filling effectiveness occur 8 ¦ ~y means of the foregoing steps, the 9 ¦ location of unacceptable regions of fill are pinpointed, 10 ¦ which regions result from a drop or decrease in filling 11 ¦ effectivensss of the filling operation. Filling 12 ¦ effectiveness, in this context, is simply the ratio of 13 1 volume actually filled to total fillable volume, or, in 14 ¦ terms of cross-section, the ratio of actual distribut~on of 15 1 fill in the cross-sectional area to total fillable -~
1~ ¦ cross-section.
17 Because of the continuous monitoring of the 1~ capacitance change as embodied in the foregoing steps, it is 19 possible, utilizing the pressnt invention, bo control the filling operation to remedy defects in the operation and 21 virtually assure maintenance of acceptable filling 22 effectiveness during the manufacturing run. Th~1s, the 24 method of the invention may include the additional steps of ~5 generating control signals in response to deviations in _ filling effectiveness to vary a parameter of the filling 26 operation to correct such deviations. These parameters j include the temperature and pressure of the filling 2a I compound, and the line speed of the moving cable as it ¦I passes through the filling stage.
Description of the Drawings Tha invention, and its mode of operation, iii Il -4-I, will be more fully understood by reference to the following detailed description and to the drawings, in which:

FIG. 1 illustrates a portion of the cable core, filling equipment, a footage counter, and monitoring equipment in schematic form;

.

FIG. 2 illustrates the monitoring equipment in diagrammatic form and the interconnections with the cable core;

FIG. 3 illustrates capacitance measuring circuitry;

- FIG. 4 illustrates encoder circuitry, a transmitter and receiver and decoding circuitry utilized in practicing the invention;

FIG. 5 illustrates waveforms which are present at various points in the measuring circuitry;

FIG. 6 illustrates a computer flow chart practiced in the invention; and FIG. 7 illustrates a graph of filling effectiveness for a particular type of cable.
Detailed Description of the Invention With reference to FIG. 1, there is shown a portion of a cable core 1, the major portion of which is shown on a pay-off reel 2, which is rotatable on a shaft 14. The core 1 is shown passing through a filling chamber, indicated generally by the numeral 3, and which is of the type described in Canadian Patent No. 1,035,914 which issued to Henry J. Freeman, et al on 8 August 1978. The core 1 advances from the filling chamber 3, over a footage counter 4, and is then taken up on a take-up reel, not shown, which is driven by suitable drive means 10. Between the filling chamber 3 and the footage counter 4 various other manufacturing operations . 1 1064109 J. A. ~udson et ~l. 4-2-2 l may take place, su~h as a final binder spirally applied to 2 the core, an aluminum sheath applied over the binder, and an 3 insulating jac~et extruded over the sheath, none of which 4 are shown, but all of which are well known operation~ in the manufacture of telecommunications cables.
6 ¦ In FIGS. 1 and 2, it may be seen that the 7 1 cable core 1 includes, in this embodiment, a plur~lity of 8 ¦ twisted pairs of insulated conductors 6. An outer twisted 9 pair of conductors 7 are connec~ed by a pair of leads 8 to ¦the input of a capacitance measuring circuit, encoder, and ll ¦transmitter, which is indicated generally as block 9, and 12 ¦which is disclosed in detail in FIGS. 3 and 4. The 13 ¦circuitry of block 9 is connected by output leads 11 to an 14 ¦input coupling coil 12, which is rotatable with the reel 2.
¦ The input coupling coil 12 is associated .
1~ ¦with an output coupling coil 13, which is stationary on the 17 ¦shaft 14. The coil 13 is co~nected by leads 16 to a receiver and decoder which is indicated generally as the l9 ¦block 17, and which is disclosed in detail in FIG. 4. .
20 ¦ In a similar manner, an inner twisted paix 21 ¦ of insulated conductors 18 (see FIG. 2) are connected over a ~:
22 ¦ pair of leads 19 to the input of a capacitance measuring 23 l circuit, encoder, and transmitter, which is indicated 24 ¦ generally as the block 21, and which is similar to the 25 l circuitry disclosed in the block 9 in FIGS. 3 and 4. The 2~ ¦ circuitry of block 21 is connected by output leads 22 to the 27 rotatable coupling coil 12, described previously. The 2~ Isignals from the leads 22 are coupled through the coil 12 to 29 ¦the stationary coupling coil 13, and through leads 23 to a 3 1I receiver which is indica~ed generally as the block 21~, and il ,1 !~ 1064109 J. A. Iludsorl et al. ~-2-2 l ~ which is similar to that disclosed in detail in the block 17 2 1 in FIG 4.
¦ It ~ay be further seen that the outputs of 4 I the receivers 17 and 24 are fed to a computer or proces30r ¦ 26, which could be a general purpose digital computer, for a 6 ¦ purpose to be described in detail subsequently.
7 ¦ The capacitance monitoring circuitry 8 ¦ contained in the blocks 9 and 17 and depicted in FIGS. 3 and ¦ 4 represent3 an arrangement for achieving a high degree of lO 1 accuracy in the monitoring process. It is to be understood, ll 1 however, that other circuit arrangements for monitoring - 12 capacitance changes might also be used, depending upon the 13 degree of accuracy and speed of response desired. While the 14 following description is directed to the circuits of blocks 9 and 17 for monitoring the capaci~ance change between the 1~ conductors 7, substantially identical circuitry is 17 represented by blocks 21 and 24 for monitoring the l~ capacitance chan~e between the conauctors 18. Because coils 19 12 and 13 are common to both monitoring branches, the circuitry of blocks 21 and 24 operates at different 21 frequencies from that of blocks 9 and 17.
22 As the filling operation progresses, the 23 mutual capacitance of the pair of conductors 7 will increase 24 because the air between conductors 7, which has a dielectric constant of 1.0, is replaced by the filling compound, which has a dielectric constant materially different from that of 27 air, such as, for example, 2.2. In addition, as the filled 2~ length of the cable core increases, the capacitance also ~9 increases as a function of length. The monitoring equipment 3o ll is operated on the principle that under routine operating 31 l¦ conditions, the outer pair of conductors 7 will-be I

i' I

~ 1064109 J, ~. Hudson et al. 4-2-Z
l approxima~ely 100% surrounde~ with the filling compound because they are at the outside of the cable core 1 as it 3 passes through the filling chamber 3.
4 In the circuit of FIG. 3, a voltage reference source 31 generates an output, preferably direct 6 current, such as a positive 5 volts, which is applied to an 7 inverting amplifier 34 via lead 32, and to one contact 42 of 8 a single pole-double throw switch 39. The output of 9 amplifier 3~ is applied by lead 37 to the other contact 38 of switch 39. Switch 39 may take any of a number of ll suit~ble forms, such as, for example, a solid state device.
12 The voltages applied to contacts 42 and 38 are depicted in 13 FIG. 5 as 33 and 36, respectively.
14 Contactor 43 of switch 39 applies either the posi~ive ~33) or negative ~36) reference voltage ~o a buffer l~ amplifier 46 via lead 44. As will be apparent hereinafter, 17 a waveform such as 45 in FIG. 5 can be made to appear on 18 lead 44 and the output lead 47 of amplifier 46 by a periodic l9 actuation of switch 39. The output of amplifier 46 is applied to the negat~ve input of a difference amplifier 21 (constan~ current generator) 48~ the output of which is 22 applied through a charging resistor 49 to the conductors 7, 23 the capacitance between which is then charged ~and 24 discharged). Amplifier 48 adds a small amount of gain to 25 the reference voltage input so that the capacitance can be -26 charged to voltages either higher or lower than the positive ~7 and negative reference voltages, respectively.
28 The charging (and discharging) of the 29 capacitances is monitored by a buffer amplifier 51, which 3~o serves to isolate the capacitance charging circuitry from ~l I the loading effects of other parts of the circuit. The 1~ -a-Il .
' ' . 1 1064109 J. A. Hudson et al. 4-2-2 l output of amplifier 51, represented by curve 55 in FIG. 5, 2 is applied via lead 66 to the plus or positive input o~

3 amplifier 48 so that, as the amplifier 48 monitors the 4 difference between its two voltage inpu~s it provides

5 through resistor 49 a constant current charging or .
discharging of the capacitance of the conductors 7. .
7 The output of amplifier 51 is also directed ¦through lead 52 to a voltage divider, made up of resistors 53 9 ¦and 54, ~he output of which, represented by curve S9 in FIG.
5, is applied to one input of each of a pair of comparators ll 57 and 58. Comparators 57 and 58 also have applied to their 12 inputs the positive and negative refexence voltages 13 respectively, over leads 41 and 37, as shown. In addition, 14 ¦ the output of amplifier 51, as represented by curve S5 of 15 l FIG..5, is applied to one input of each of a pair o 1~ comparators 63 and 64, whose other inputs have applied 17 thereto the positive and negative reference voltages over l~ leads 41 and 37, respectively.

2 The outputs of comparators 57 and 58 are 2 applied to a flip-flop circuit 61, whose output is used to 22 control switch 39. S~here the input waveform 59 (FIG. S) to 23 comparator 57 equals or is greater than the positiYe 2'' reference voltage on lead 41, the comparator 57 produces an joutput to set the flip-flop 61 and in turn activate switch 139 so that contactor 43 engages contact 38, and the negative 26 Ireference voltage is applied to amplifier 46. Conversely, !1 if the input waveform 59 (FIG. 5) equals or is more negative 2& Ithan the input on lead 37 to comparator 5~, comparator 58 ~9 ~generates a signal to reverse the flip-flop 61 and hence switch 39, thereby applying the positive reference voltage to amplifier 46. Through the action just described, the !1 9 ~ ¦ 1064109 J. A. Hudson et al. 4-2-2 l ¦ waveform 45 of FIG. 5 is generated and applied to difference ¦ amplifier 48.
3 1 It can be seen that the circuitry thus far 4 ¦ described monitors the charging of the capacitance of 5 ¦ conductors 7 until the charge reaches a specified reference

6 ¦ level, then causes the capacitanca to discharge ana recharge

7 ¦ in the opposite direction to a specified refexence level.

8 1 In order to obtain a proper evaluation of the chang~ in

9 ¦ capacitance, it is desirable to monitor the time span of lO ¦ the charging and discharging cycles. This is accomplished 11 1 in the arrangement of FIGS. 3 and 4 by comparators 63 and 64 12 ¦ and associated circuitry.
13 l As de~cribed previously, the output of 14 ¦ buffer amplifier 51 follows the charging and discharging of 15 l the capacitance of the conductor pair 7, the resulting 1~ 1 waveform being represented by curve 55 of FIG. 5, and 17 l applies its output to the comparators 63 and 64. The 18 ¦ outputs of comparator~ 63 and 64 are applied to the two 19 inputs of a NOR gate 67, as shown. Absent any signal to either of its inputs, NOR gate 67 supplies a true or on 21 signal in a known manner, but when a signal appears at 22 eLther input, the gate shuts, or otherwise indicates an off 23 condition. When the signal applied to comparator 63 from 24 amplifier 51 is less than that on lead 41, comparator 63 produces no output. In like manner, when the signal from 26 a~plifier 51 to comparator 64 is greater than that on lead ~7 1 37, comparator 64 produces no output. Under these 28 !!conditions, NOR gate 67 gives an on indication. However, 2~ il when the input to comparator 63 from amplifier 51 equals or 3 , exceeds the signal on lead 41, compara~or 63 produces an - ,, output which switches NOR ga~e 67 off. By the same token, !, . I

-10-. : . , , : . , . .

1 0 6 4l 09 ~. A. Hud~un et al. 4-2-Z

1 Iwhen the signal from amplifier 51 to comparator 64 equals or 2 lis less than that on lead 37, comparator 64 produces an 3 ¦ output which turns gate 67 off. Thus when waveform 55 of -4 1 FIG. S is applied to comparators 63 and 64, the resulting ¦output of NOR gate 67 is represented by waveform 68 of FIG.
6 ¦ 5~ with the length or duration of the charging cycle being 7 ¦ given by the on period T. It can be appreciated that as the 8 ¦ cable is filled, the p~riod T will increase, due to the 9 ¦ increased capacitance and hence the increased charging and lO ¦ discharging times, which.:decreases the slopes of waveforms ll ¦ SS and 59.
12 ¦ In FIG. 4 it can be seen that the output of 13 1 NOR gate 67 is applied to one input of an AND gate 69, whose 14 oth~x input has clock signals applied thereto from a crystal oscillator clock 70. .The output of gate 69 is applied to a l~ binary counter 71. It can be seen that during each period T
17 f waveform 68 of FIG.~5, i.e., when NO~ gate 67 is giving a l~ tru2 or on indication, a series of digital pulses at the 19 c70ck frequency are applied to counter 71, which counts the pulses and outputs to a shift register 72 binary numbers 21 indicative.of the length of the period T.. A timing and 22 control circuit 73 which receives s~gnals o~er lead 65 from 23 i flip-flop 61 resets counter 7i at each change of condition 24 ¦ f flip-flop 61, and at the same tLme empties shift register .
25 l 72 in a serial data stream to a variable modulus divider 74.
20 ¦l. Thus the counting cycle of counter 71 is made to coincide ~7 1I with the charging and discharging cycles of the capacitance 2~ ¦I being monitored. Further, the actual count itself indicates .
2~ 1l the length of the charging or discharging cycle, and changes 30 ! (increases) as the ~illing operation progresseQ.

~ I ' ,, ~i ~ i 1064109 ~. ~. ilud~on et al. 4-2-2 j l ~ Variable modulus divider 74 receives an 2 ¦input from clock 70 as well as from shift register 72, and 3 I produces a pair of output frequencies, such as 6.25 RHZ and 5.68 KHZ, ane of which represents binary 1~s of the signal ¦from the shift register and the other of which represents 6 1 binary O's of the same signal. The output of divider 74 is 7 ¦ passed through a low pass filter 76 to the rotatable, 8 ¦ coupling coil 12 as signals indicative of the charging ¦capacitance of conductors 7.
¦ At this stage of the operation of the

11 1 monitoring system illustrated in FIG. 1, there have been

12 ¦ created audio frequency signals which indicate the changing

13 ¦ capacitance of conductors 7 as the filling operation

14 ¦ progresse~. In a like manner, similar signals will have been generated by the circuitry of transmitter 21 to l~ indicate the changing capacitance of conductors 18. It is 17 possible to operate with these signals to achieve the 18 desired comparisons and hsnce a measure of the filling 19 effectiveness in a number of ways. The remaining circuitry of FIG. 4 illustrates one arrangement for achieving the 21 desired results. -The audio frequency signals in coi~ 12 are 23 picked up by coil 13 and applied via leads 16 to a band pass 24 filter 77. Filter 77 functions to pass those frequencies I indicative of the capacitance and capacitance change~ of 26 j conductors 7. A similar filter in receiver 24 passes only ~7 ¦I those frequencies indicative of the capacitance and ¦I capacitance changes of conductors 18.
29 !I The filtered signal is applied to a 3 ,, converter 78 t~hich generates a voltage output having a 3 magnitude determined by which fre~uency t6.25 KI~Z or 5.68 ,1' ll -12-~1 .
' ~ 1064109 J. A. Nudson et al. 4-2-2 ¦
1 IKHZ) is applied to its input. The output of the converter 2 lis applied to a voltage comparator 79 which generates a 3 ¦binary number indicative of which voltage was received at 4 1 its input, and its binary output is applied to a shift register 81. The comparator 79 and the shift register 81 6 ¦ continuously receive the asynchronous serial data 7 ¦ transmission from the transmitter.
8 ¦ The output of comparator 79 is al50 applied -9 1 to a synchronization logic circuit 83 which recognizes when lO ¦ a complete signal word is present in shift register 81 and ll ¦ signals a data latch circuit 82, connected to the output of 12 ¦ register 81, to store the word. The latch circuit then 13 ¦ generates a read command signal which is applied tprough 14 lead 85 to computer 26, and the computer reads and stores the signal input from the latch circuit applied over leads 16 86. The binary signals received by computer 26 over leads 17 86 are indicative of the capacitance change between 18 conductors 7 as the filling operation progresses. Footage l9 counter 4 (FIG. 1) also applies signals over leads 88 to computer 26. At the same time, signals representing the 21 capacitance change between conductors 18 are applied bo the 22 computer 26 over leads ~7. The signal from counter 4 is 23 preferably a pulse per distance indication, such as, for 24 example, one pulse per foot of cable 1 passing over it.

The operation of the computation steps performed by computer 26 can best be understood with 27 i reference to FIG. 6, a computer flow chart. As was pointed 23 ¦¦ out in the foregoing, the signals applied to coil 12, along 9 l~ with the footage signals, contain the necessary data for 3 1I computing the filling effectiveness of the filling 31 operation. The circuitry of receiver 17 (FIG. 4) is !~ -13-Ii .

~ . 1064109 ~ ludson et al. 4-2-2 ¦
1 designed to prepare this information for use by computer 26, 2 ¦ but it is to be understood ~hat the following operations 3 ¦could be performed by means other than a computer, if 4 ¦desired.
5 ¦ In the flow chart of FIG. 6, box 91 represents the data inputs to computer 26. ~he computer 26 7 ¦ then determines the increase of capacitance per unit lengths 8 ¦ f cable 1 processed, or the slope, for the outside twisted 9 ¦ pair of conductors 7 and for the inside twisted pair of ¦conductors 18, by dividing the change of capacitance by the 11 ¦ change of processed footage of filled cable~ as shown in box 2 ¦ 92 of FIG. 6.
3 1 The computer 26 then compares the der~ved 4 1 slope of the capacitance of the outside pair of twisted conductors 7 to a predetermined slope value and calculates ~ the percent difference in capacitance between the two, if 187 any. The predetermine~ slope value is figured on the basis of a filled cable having an average mutual capacitance of 83 l9 nanofarads per mile of length. This is shown as box 93 of 21 FIG. 6.
22 The computer 26 also performs the same -23 compu~ations wi~h respect to the inside pair of twisted 24 conductors 18, to determine the percent difference in capacitance, but comparing with the outside pair capacitance slope value, as shown as box 94 of FIG. 6.
26 The computer 26 then is used to determine or 27 calculate ths filling effectiveness for the outside pair of 28 twisted conductors 7, as shown as box ~6 of FIG. 6.
29 The filling effectiveness is determined from 3o l the mutual capacitance difference, and is a function of two 31 significant variables. The first variable to be considered 1~

1, -14-i~

`

~1 1064109 J. A. Nudson et al. ~-2-2 i 1 ~ is the geometric spacing of the ~wo insulated conductors 7 2 ¦ with respect to each other and with respect ~o the other 3 ¦ insulated conductors 6 in the cabla 1. The second variable 4 ¦ is the dielectric constant of the insulating material ¦ surrounding the conductors and entering the interstices 6 ¦ ~herebetween.
7 ¦ However, from a practical standpoint, it may 8 ¦ be assumed ~hat the variable of the geometric spacing ~ill 9 ¦ remain relatively constant throughout the cable filling ¦ process, and so may be assumed constant in the computations.
11 ¦ This, then, leaves the dielectric constant of the insulating 12 ¦ material surrounding the conductors ~o be taken into 13 ¦ consideration, but must be computed in terms of mutual .
14 ¦ capacitance.
¦ The filling effectiveness, as mentioned 16 earlier, is defined as an indication of the fillable 17 cross-sectional area which has been filled with 18 waterproofing compound as compared to the total 19 cross-sectional area that could be filled to result in 100 fill.
21 Further, the portion of fillable area filled.
22 with.the compound relative to the total fill~ble area is a 23 function of the dielectric constant of the total fillable 24 area.
Thus, the filling effectiveness may b~
26 I determined by using the following equation:

28 ¦ Pilling = ~ tEF ~ Ep~) (1 ~ 2 EpJ) 100 29 Ef ectivenes~ ~ ~E~ + 2EpJ) (1 - Ep3 ~ 1064109 J. A. Huùson et al. 4-2-2 1 ~ Where: E F= Dielectric Constant of Fillable Area l of Cable 3 ¦ E p~- Dielectric Constant of Pure Filling 4 ¦ Compound.
¦Then by measuring the change of this dielectric constant the ¦amount of filling compound which has been added may be 7 ¦determined.
8 ¦ However, this change cannot be measured 9 ¦ directly, but an equation must be used which relates this ¦change to total change in mutual capacitance, which can be 11 ¦measured. Such an equation is:
2 ¦ ~E F = ~E tREF REI I EFMin . ~
14 ¦ (EI ~ REI) Where EFMaX = Maximum va~ue of E for 100%
1~ filled 17 ~Min = Air ~ 1.00 l$ E = Overall dielectric constant 19 EI = Dielectric constant of insulation on conductors 21 R = Mutual capacitance with no fili . ._ .
22 Mutual capacitance with 100X fill.
23 If the value, or equation, fQr EF is 24 substituted in the equation set forth previously, it will be possible to solve for the filling effectiveness.
26 However, the first set forth equation may be 28 further simplified, using a specific type of cable.
29 As an example, in te~ting one type of cable 0 in manufacture, such as polypropylene insulated conductors 3 and the cable having a mutual capacitance of 83 nanofarads 1~' _ . 1064109 J. A. Hudson et al. 4-2-2 per mile, the equation will be:
2 Filling = 100-50 ~ 1 1 %
3 ¦ EffectivenPss Ll9 4 ~ .224~
4 Where: ~E = Difference in capacitance between the 6 outside pair and a predetermined value or difference in inside and outside 7 capacitances (Boxes 93 and 94, PIG. 6) 8 With the cable of the present example, the 9 percent ~E is limited to the range 0-16.
All of the above computations are indicated 11 as being performed in boxes 96 and 103, FIG. 6.
12 FIG. 7 is a ~urve illustrating the above 13 equation for filling effectiveness as a function o~ the 14 percent difference in mutual capacitance, or the type of cable mentioned above.
1~ As mentioned previously, under normal 17 operating conditions it is assumed that ~he outer twisted 18 pair of conductors 7 receive a 100S fill. If this is in 19 fact occurring when the slope is calculated in box 93, FIG.
1 6, the filling e~ectiveness will be calculated with the 21 1 resultant calculation being equal to a maximum 100% in box 22 ~ 96. However, if this does not occur the filling 3 effectiveness will be calculated, box 96, FIG. 6. If the 24 result is less than the p~edetermined value the computer 26 26 will supply signals over a pair of leads 98, FIG. 1, to ~7 control a valve 99 in thP filling cham~ar 3 to increase the l pressure of the filling compound ~o attempt to reach the 29 1 predetermined fill condition on the outer twisted pair of l conductors 7. Such is shown as box tO1 in FIG. 6. The 3o ~ valve 99 may be a digital flow valve such as Model 6-607D of 31 Digital Dynamics, Inc. of Sunnyvale, California.

!~ -.7 ¦! .

~ 1064109 J. A. Uudson et al. 2-4-2 2 Further, the computer 2G also may siynal over a pair of leads 102, FIG. 1, to increase the-3 temperature to the filling chamber 3 to cause the filling 4 compound to be less viscous. Still further it is possible :
for the computer to generate signals for controlling drive o' means 10 through leads 110 to alter the line speed of the 7 advancing cable 1. -8 Obviously, the computer 2~ may generate 9 signals to control either one, or combination, or all of the above mentioned variables, as itiis continuouslv monitoring l1 the relative filling effectiveness.
12 The computer 26 also calculates the filling 13 effectiveness on the inside twisted pair of conductors 18, 14 using the equations set forth above, as sho~ in box 103, FIG. 6. The calculated value may not be the same as 16 calculated for the outside twisted pair of conductors 7 (box 17 96, FIG. 6), as the slopes may be different (see boxes 93 :.
18 and 94, FIG. 6).
l9 In the event that the calculated value is determined to be less than a predetermined requirem~nt as 21 determined in box 104, ~IG. 6, the computer 26 will generate 22 signals to control the variables, box 106, ~IG. 6. These 23 siqnals will be similar to those generated in box 101, FIG.
24 6, to similarly control the pressure or temperature of the filling compound or the line speed of the cable 1.
¦ During the operation of the equipment the 27 computer 26 will send si~nals over a pair of leads 107 to 28 cause the results of the continuous monitoring of the 29 fill~ng effectiveness to be recorded on a recording device 3o 10~. The recording may he a series of actual value readings 3l ~ on a print-out wit}1 corresponding footage values of filled Il -1 8-- 1064109 J. A. I~udson et al. 2-4-2 1 cable core 1, or may be a plotting of data and footage, such 2 as that calculated in the boxes 96 and 103, PIG. 6.
3 In the alternative, it is possible to obtain 4 the filling effectiveness of the cable, but not as pre~isely as described above, by measuring the caoacitance change of a 6 ~ single twisted pair of conductors, preferably near the 7 center of the cable, such as the twisted pair 18. The 8 signals indicative of such capacitance would be handled in a 9 , manner similar to that described above and placed in the 10 ,l computer 26. The computer 26 would also have a standard 11 ~ capacitance change stored thersin for the particular typ~ of !
12 ,i cable being filled, and would process the measured change as ¦
13 i~ by using boxes 93, 96, 97, 101, and 108, FIG. 6. I
14 It is to be understood that the above- j

15 ~ described arrangements are simply illustrative of the

16 ,j principles of the invention. Other arrangements may be

17 , devised by those skilled in the art which will embodv the

18 ~ principles of the invention and fall within the spirit and

19 1 scope thereof. ¦ -1. , I
'' I
.

.i .

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of monitoring the amount of fill being placed in a cable as the cable is advanced through a filling chamber, which comprises the steps of continuously monitoring the changing capacitance of a twisted pair of conductors in the cable, and comparing the monitored changes in capacitance to a predetermined standard value of capacitance change.

2. A method of measuring the filling effectiveness of the filling operation in the manufacture of waterproof cables having a plurality of conductors therein, which comprises the steps of:
continuously monitoring the change in capacitance of an outer pair of conductors as the cable passes through a filling chamber, continuously monitoring the change in capacitance of an inner pair of conductors as the cable passes through the filling chamber, and comparing the monitored changes in capacitance of the outside pair and the inside pair with each other to ascertain the filling effectiveness of the filling operation.

3. The method according to claim 1, and further including the step of providing an indication of the location along the cable length of regions where deviations in filling effectiveness occur.

4. The method according to claim 1, and further including the step of comparing the monitored capacitance change of the outer pair of conductors to a predetermined reference value.

5. Apparatus for measuring the filling effectiveness of the filling operation in the manufacture of waterproof cables having a plurality of conductors comprising:
first means for continuously measuring the change in capacitance of an outer pair of conductors in the cable as it passes through a filling chamber, second means for continuously measuring the change in capacitance of an inner pair of conductors in the cable as it passes through said filling chamber, and means associated with said first and second means for generating signals indicative of the changes in capacitance of the conductors as the changes occur.

6. Apparatus according to claim 5 and further comprising:
means for determining the filling effectiveness including means for comparing the change in capacitance of the outer pair of conductors to the change in capacitance of the inner pair of conductors.

7. Apparatus for measuring the filling effectiveness of the filling operation in the manufacture of waterproof cables having a plurality of conductors comprising:
means including a voltage source for continuously charging and discharging the capacitance of a pair of the conductors between upper and lower voltage limits;
comparator means responsive to the charge on the capacitance reaching a charging limit for generating a signal to reverse the voltage applied to the capacitance;
second comparator means for providing an indication when the charge on the capacitance exceeds the upper and lower voltage limits;
means for generating a pulse train in the absence of such an indication from said second comparator means; and means for counting the pulses generated between such indications, the number of pulses indicating the charging and discharging times of the capacitance.

8. Apparatus according to claim 7, wherein the pair of conductors is a first pair of conductors, and further including:
means for continuously charging and discharging the capacitance of a second pair of conductors between upper and lower voltage limits;
third comparator means responsive to the charge on the capacitance of the second pair of conductors reaching a charging limit for generating a signal to reverse the voltage applied to the capacitance;
fourth comparator means for providing an indication when the charge on the capacitance of the second pair of conductors exceeds the upper and lower voltage limits;
means for generating a second pulse train in the absence of such an indication from said fourth comparator means; and means for counting the pulses generated between such indications, the number of pulses indicating the charging and discharging times of the capacitance of the second pair of conductors.

9. Apparatus according to claim 8 and further including:
means for converting the pulses into signals indicative of the changing capacitance of the first pair of conductors and of the second pair of conductors, and means for comparing the signals representative of the changing capacitance of the first pair of conductors to the signals representative of the changing capacitance of the second pair of conductors for determining the filling effectiveness of the filling operation.

10. Apparatus according to claim 9 wherein said last-mentioned means includes means providing an indication of deviations in filling effectiveness.

11. Apparatus according to claim 10 and further including means for monitoring the cable travel through a filling chamber to provide an indication of where along the cable length deviations in filling effectiveness occur.