FI68325B - FREQUENCY REQUIREMENTS FOR FRAMSTARING AV EN I LAUNSRIKTNINGEN VATTENTAET KABEL - Google Patents

Description

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^ ™ UTLÄGGNINGSSKRIET 68325 C Patent ayönr.ctty 12 08 1935 'Patent seddelat (51) Kv.ik. * / Lnt.a. * G 01 R 31/02 // H 01 B 13/00 FINLAND FINLAND (21) Patent application - Patentansökning 763677 (22) Date of application - Ansöknlngsdag 21 1 2 76 (FI) 'f (23) Starting date - Giltighetsdag 21.12 76 (41) Has become public - Blivit offentlig 2 ^ 06 77

National Board of Patents and Registration Date of publication and publication. -

Patent- and Register Styrelsen '' Ansökan utlagd och utl.skriften publlcerad 30.04.85 (32) (33) (31) Privilege requested — Begird priority 22.12.75 02.11.76 USA (US) 642852, 737752 (71) Western Electric Company , Incorporated, 195 Broadway, New York,

New York 10007, USA (72) James Alphus Hudson, Jr., Atlanta, Georgia, Raymond Alexander Levandoski, Doraville, Georgia, Allen Kyle Long, Roswell, Georgia, USA (74) Berggren Oy Ab (54) This invention relates to a method and apparatus for making a filled, longitudinally waterproof cable comprising a plurality of outer and inner pairs of outer and inner conductors. per inner and outer pair of conductors and the degree of filling of the cable is determined on the basis of said measurement by calculation.

It is desired that the communication cables, especially those intended for burial in the ground, be moisture resistant in order to prevent transmission difficulties caused by moisture leaking into the cable. In general, such dehydration is carried out during the manufacture of the cable by filling the interior of the cable with a suitable filler compound, for example petrolatum or a mixture of petrolatum and polyethylene. To achieve the desired results, it is desired that the filler substantially substantially fill the volume of the cable that is not occupied by the conductors and other cable components, including the spacing of the twisted pair of conductors. Various methods and apparatus for filling cables are already known, cf. e.g., U.S. Patent Nos. 3,832,215, 3,854,444, 3,850,139, 3,789,099, 3,876,487, and 3,733,225.

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Normal filling operations involve the introduction of a filling compound after the heart has been formed and before the final dressing and sheath have been placed on the heart. At this stage of manufacture, the core is relatively compact and it is difficult to introduce a filler compound into it, however, preventing moisture penetration in subsequent use requires a large relative fill of the total fillable volume, preferably evenly distributed across the entire cable cross-section.

Numerous arrangements have been designed to check the (relative) amount of filler in the cable, which is an indication of the efficiency of the filling operation. One such arrangement involves cutting off the end of the final cable and subjecting the other end to a known water pressure. If more than a predetermined amount of water flows out of the other end, the cable is not acceptable. The second arrangement involves weighing the short length of the filled cable. Since the weight of the unfilled cable is known and the weight of the correct amount of filler for this cable length can be determined, the weight of the filled cable length must be at least equal to the sum of the former two weights for the cable to be acceptable.

Yet another method for determining the acceptability of a filled cable involves measuring the capacitance among the outer conductor pairs of the final cable, then measuring the capacitance among the inner conductor pairs, and comparing the two measurements. The difference between the two measurements divided by the outer measurement gives a measure of the filling efficiency, which can then be compared to empirically determined values to check whether the cable is acceptable or not.

In the previously known methods for determining the filling efficiency, examples of which are given above, the operation is performed with the final cable, therefore if if the filling efficiency is found to be unsatisfactory, the entire cable run must be scrapped or a cable refilling must be attempted. In those processes where measurements or tests are performed on a short cable length, there is no way to determine if the remainder of the cable is similar to the sample tested, resulting in a calculated risk depending on the test results. In arrangements where the entire cable length is tested, such as in a capacitance measurement method, the indication of non-acceptability can only be due to a very short defective portion of the cable that could be cut off if its location along the cable length were known.

The latter dilemma is common in virtually all prior art arrangements, as there is no way to ensure where for a portion of the cable length the filling has fallen below an acceptable minimum. An additional disadvantage of the previously known testing methods is that they are performed with final cables and the unacceptable cable must be scrapped or refilled, which means both extra time and extra money.

The above problems are avoided by the method according to the present invention, the features of which are apparent from the appended independent claim. The features of the apparatus according to the invention appear correspondingly from claim 3.

The above steps identify the locations of the unacceptable areas of the filling, which areas are the result of a decrease in the filling efficiency of the filling operation. The filling efficiency in this context is simply the ratio of the volume actually filled to the total volume that can be filled or, in the case of cross-section, the ratio of the actual distribution of the filling to the total cross-sectional area to be filled at the cross-sectional area.

Due to the continuous monitoring of the change in capacitance carried out in the above-mentioned steps, it is possible using the present invention to control the filling operation to eliminate the defects in operation and to effectively ensure that an acceptable filling is maintained during the manufacturing run. Thus, the method of the present invention took. includes additional steps of generating control signals depending on the filling efficiency deviations to change any parameter of the filling operation to correct such deviations, the wedding parameters including the temperature and pressure of the filling compound and the line speed of the moving cable as it passes through the filling step.

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The invention and its mode of operation will become more fully understood upon consideration of the following detailed description and accompanying drawings.

Figure 1 illustrates a part of the cable core, filling device, length counter and monitoring device in schematic form.

Figure 2 illustrates the monitoring device in diagrammatic form and the connections with the kaa game core.

Figure 3 illustrates the capacitance measurement circuit.

Figure 4 illustrates an encoding circuit, a transmitter and a receiver, and a decoding circuit used in the practice of the invention. Figure 5 illustrates the waveforms that occur at different points in the measurement circuit.

Figure 6 illustrates a computer flow chart used in the practice of the invention.

Figure 7 shows graphically the filling efficiency for a particular type of cable.

Figure 1 shows a part of a cable core 1, most of which is illustrated by a output coil 2 which can rotate about an axis 14. The core 1 is described as passing through the filling chamber 3. The core 1 passes through the filling chamber 3, over the length counter 4 and is then taken to a take-up reel (not shown) operated by suitable actuators 10. Several other manufacturing operations can take place between the filling chamber 3 and the length counter 4. such as spiral winding of the final bandage over the core, placing the aluminum sheath on the bandage, and extruding the insulating sheath over the aluminum sheath, none of the functions of which are shown, but all of which are known functions in the manufacture of telecommunication cables.

It can be seen from Figures 1 and 2 that the cable core 1 in this embodiment comprises a number of twisted pairs of insulated conductors 6. The outer twisted pair 7 is connected by two conductors 8 to an input in a capacitance measuring circuit, an encoder, and a transmitter, generally indicated by block 9, shown in detail in Figures 3 and 4. The circuitry of block 9 is connected by output conductors 11 to an input switch coil 12 with coil 2.

The input switch coil 12 is connected to an output switch coil 13 which is 68325 in place on the shaft 14. The coil 13 is connected by wires 16 to a receiver and decoder, generally indicated by block 17, shown in detail in Figure 4.

Similarly, the inner pair of insulated conductors 18 (see Figure 2) is connected by two conductors 19 to an input in a capacitance measuring circuit, an encoder and a transmitter, generally indicated at block 21 and similar to the circuitry of block 9 (see Figures 3 and 4). The circuitry of the block 21 is connected to the rotating switch coil 12 by the output conductors 22, which has already been mentioned above. The signals from the conductors 22 are connected via a coil 12 to a stationary switch coil 13 and via the conductors 23 to a receiver 24, which is similar to block 17 and is described in detail in Figure 4.

It can be further seen from the figures that the outputs of the receivers 17 and 24 are fed to a computer, i.e. a processor 26, which may be a digital general purpose computer, for a purpose which will be explained in detail below.

The capacitance monitoring circuit included in blocks 9 and 17 and illustrated in Figures 3 and 4 represents an arrangement that achieves very high accuracy in the monitoring process. However, it is to be understood that other circuit arrangements may also be used to monitor changes in capacitance depending on the desired accuracy and response rate. Although the following description is directed to the circuits of blocks 9 and 17 for monitoring changes in capacitance between conductors 7, blocks 21 and 24 represent substantially similar circuits for monitoring changes in capacitance between conductors 18. Because coils 12 and 13 are common to both monitoring branches, the circuits of blocks 21 and 24 operate at different frequencies than the circuits of blocks 9 and 17.

As the filling operation progresses, the mutual capacitance of the pair of conductors 7 increases, because the air between the conductors 7, which has a dielectric constant of 1.0, is replaced by a filler whose dielectric constant is substantially different from that of air, for example 2.2. In addition, as the filled length of the cable core increases, so does the capacitance with the length. The monitoring device is operated on the principle that under routine operating conditions the outer pair of conductors 7 is approximately 100% 68325 surrounded by a filling compound, since this pair of conductors is located on the outer surface of the cable core 1 as the core passes through the filling chamber 3.

In the circuit shown in Figure 3, the reference voltage source 31 generates an output, preferably a DC voltage, e.g., 5 volts, which is passed through a conductor 32 to a reversing amplifier 34 and via a conductor 41 to a single contact 42 in a single-pole two-position switch 39. The output of an amplifier 34 is The switch 39 may take any of a number of suitable forms, for example a solid state device. The voltages applied to the contacts 42 and 38 are indicated in Fig. 5 by reference numerals 33 and 36.

The contact portion 43 of the switch 39 conducts either a positive 33 or a negative 36 reference voltage to the buffer amplifier 46 via a line 44. As will be seen below, e.g., the waveform of Fig. 5 can be caused to occur in line 44 and output line 47 of amplifier 46 by periodically activating switch 39. The output of amplifier 46 is conducted to the negative input of differential amplifier (constant current generator) 48, etc. the output of the amplifier is connected via a resistor 49 to conductors 7, between which the capacitance then becomes charged (and discharged). Amplifier 48 adds a small amount of gain to the reference voltage input so that the capacitance can be charged to either higher or lower voltages than the positive and negative reference voltages.

Capacitance charging (and discharging) is monitored by a buffer amplifier 51, which serves to separate the capacitance charging circuit from the load effects of the other parts of the circuit. The output of amplifier 51, represented by curve 55 in Figure 5, is passed through line 66 to the positive input of amplifier 48. so that when the amplifier 48 monitors the difference between its two voltage inputs through the resistor 49 it provides a constant current charge or discharge to the capacitance of the conductors 7.

The output of the amplifier 51 is also directed via a line 52 to a voltage divider formed by resistors 54 and 53, the output of which, represented by curve 59 in Figure 5, is provided as a single input to each comparator of the pair of comparators 57 and 58. A positive and a negative reference voltage is applied to the inputs of the comparators 57 and 58 via the conductors 41 and 37.

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In addition, the output of the amplifier 51, represented by the curve 55 in Fig. 5, is applied to both inputs of the comparators 63 and 64, to the second inputs of the comparators of which a positive and negative reference voltage is applied via the conductors 41 and 37.

The outputs of comparators 57 and 58 are applied to a flip-flop circuit 61, the output of which is used to control switch 39. When the input waveform 59 (Fig. 5) to comparator 57 is equal to or greater than the positive reference voltage at line 41, comparator 57 produces output flip-flop. 61 and in turn activate the switch 39 so that the contact member 43 contacts the contact 38 and the negative reference voltage is applied to the amplifier 46. Conversely, if the input waveform 59 (Fig. 5) is equal to or more negative than the input in line 37 to comparator 58, the comparator generates a signal to reverse the flip-flop 61 and thus to reverse the switch 39, whereby a positive reference voltage is applied to the amplifier 46. The operation just described generates the waveform 45 of Fig. 5 and this is applied to the differential amplifier 48.

It can be seen that the connection described so far monitors the charging of the capacitance of the conductors 7 until the charge reaches a certain reference level, then causes the capacitance to be discharged and the capacitance to recharge in the opposite direction to the specified reference level. In order to achieve a consistent assessment of the change in capacitance, it is desirable to monitor the interval between charge and discharge cycles. This is accomplished in the arrangement shown in Figures 3 and 4 by comparators 63 and 64 and associated circuits.

As described above, the output of the buffer amplifier 51 follows the charging and discharging of the capacitance of the pair of conductors 7, the resulting waveform is represented by curve 55 in Figure 5, and leads its output to comparators 63 and 64. The outputs of comparators 63 and 64 are derived input. When a signal is missing from both inputs, the NOR gate produces a true signal in a known manner, but when a signal occurs at either input, the gate closes or otherwise indicates a non-position. When the signal from the amplifier 51 to the comparator 63 is smaller than the signal from the line 41.

68325 8 comparator 64 produces a non-output.

In the same way that the signal from amplifier 51 to comparator 64 is larger than the signal on line 37, comparator 64 produces non-output. Under these conditions, the NOR gate gives an on-indication. However, when the input of the comparator 63 from the amplifier 51 is equal to or greater than the signal on the line 41, the comparator 63 produces an output which switches the NOR gate 67 to the non-position. By the same token, when the signal from amplifier 51 to comparator 64 is equal to or less than the signal on line 37, comparator 64 produces an output that turns gate 67 to a non-position. Thus, when the waveform 55 of Figure 5 is applied to comparators 63 and 64, the resulting output from the NOR gate 67 is represented by the waveform 68 of Figure 5, the length or duration of the charge period being given by the on-period T. It can be seen that when the cable is filled, period T increases due to the increased capacitance and the consequent increased charging and discharging times, which reduces the slope of the waveforms 55 and 59.

It can be seen from Figure 4 that the output of the NOR gate 67 is applied to one input of the AND gate 69, to the other input of which clock signals are applied from the crystal oxilator clock 70. The output of the gate 69 is applied to a binary counter 71. It can be seen that during each period T, . when the NOR gate 67 gives a true or on indication, a series of digital pulses at the clock frequency are applied to a counter 71 which counts the pulses and provides the shift register 72 with binary numbers indicating the length of the period T. The thinking and monitoring circuit 73, which receives signals from the flip-flop 61 via the line 65, resets the counter 71 with each state change of the flip-flop 61 and simultaneously clears the transfer register 72 as a serial data flow to the variable module divider 74. Thus, the calculation period of the calculator 71 is made to coincide with observable capacitance charging and discharging cycles. Further, the actual calculation itself indicates the length of the charging and discharging period and changes (increases) as the filling operation progresses.

The variable module divider 74 receives the input from the clock 70 and the shift register 72 and produces two output frequencies, e.g.

6.25 kHz and 5.68 kHz, one representing binary 1 of the shift register signal and the other binary 0. The output 68325 of the divider 74 is passed through a low-pass filter 76 to a rotatable switching coil 12 as signals indicating the charge capacitance of the conductors 7.

At this stage of the monitoring operation, the system shown in Fig. 1 has generated audio frequency signals indicating the varying capacitance of the conductors 7 as the filling operation progresses. Similarly, similar signals are generated in the circuit of the transmitter 21 to indicate the variable capacitance in the conductors 18. It is possible to operate these signals to achieve the desired comparison and thus measure the charging efficiency in several different ways. The remainder of the circuit shown in Figure 4 illustrates one arrangement for achieving the desired results.

Audio frequency signals in coil 12 are received by coil 13 and passed on wires 16 to a bandpass filter 77. Filter 77 passes those frequencies that describe capacitance and capacitance changes in conductors 7. A similar filter in receiver 24 passes only those frequencies that indicate capacitance and capacitance 18 in conductors.

The filtered signal is applied to a converter (converter) 78, which generates a voltage output, the magnitude of which is determined by which frequency (6.25 kHz or 5.68 kHz) is applied to its input. The output of the converter (converter) is applied to a voltage comparator 79 which generates a binary number indicating which voltage was received at its input and its binary output is applied to a shift register 81. The comparator 79 and the shift register 81 continuously receive asynchronous serial data from the transmitter.

The output of comparator 79 is also fed to a logic synchronization circuit 83 which knows when a complete signal word is in the shift register 81 and signals a data latch circuit 82 connected to the output of register 81 to store the word. The latch circuit then generates a read command signal which is routed to computer 26 via line 85 and this reads and stores the signal in the latch circuit via lines 86. The binary signals received by the wires 86 of the computer 26 indicate a change in capacitance between the wires 7 as the filling operation progresses. The length counter 4 (Figure 1) also provides signals to the computer 26 via wires 88. At the same time, signals representing the change in capacitance between conductors 10 68325 18 are fed to computer 26 via wires 87. The signal of law 4 is preferably a pulse per unit length, for example one pulse per meter of cable passing it.

The operation of the calculation steps performed by the computer 26 can best be understood by looking at the computer flow chart shown in Figure 6. As already mentioned above, the signals applied to the coil 12 together with the length signals contain the necessary information for calculating the filling efficiency of the filling operation. The circuitry of the receiver 17 (Figure 4) is designed to prepare this information for use by the computer 26, but it should be understood that the operation described in the follower could be performed by means other than a computer, if desired.

In the flowchart of Figure 6, block 91 represents data inputs to computer 26. Computer 26 then determines the increase in capacitance per unit length of cable 1, i.e. slope, for outer twisted pair 7 and inner twisted pair 18 by dividing capacitance change by .

The computer 26 then compares the thus obtained slope of the capacitance of the outer twisted pair of conductors 7 with a predetermined slope value and calculates the percentage value of the capacitance difference between the two, if this is considered necessary. The predetermined slope value is calculated on the basis of a filled cable with an average mutual pair capacitance of 52 nF / km. This is indicated in block 93 of picture 6.

Computer 26 also performs the same calculations on the inner twisted pair of conductors 18 to determine the percentage difference in capacitance, but compared to the slope value of the capacitance of the outer pair, as shown in block 94 of Figure 6.

The computer 26 is then used to calculate the filling efficiency for the outer twisted pair 7 as shown in block 96 of Figure 6.

The filling efficiency is determined by the difference in mutual capacitance and 68 3 25 it is a function of two significant variables. The first variable to be considered is the geometric distance between the two insulated conductors 7 from each other and from the other insulated conductors 6 in the cable 1. The second variable is the dielectric constant of the insulating material that surrounds the conductors and enters the spaces between them.

However, as a practical starting point, it can be assumed that the geometric distance variable remains relatively constant throughout the entire cable filling process and thus can be assumed to be constant in the calculations. This thus leaves the dielectric constant of the insulating material surrounding the conductors as a variable to be taken into account, but it must be calculated in terms of mutual capacitance.

Filling efficiency, as mentioned above, is defined as an indication of the cross-sectional area to be filled that has been filled with a waterproofing compound compared to the total cross-sectional area that could be filled to result in 100% filling.

Further, the portion of the fillable area filled with a compound relative to the total fillable area is a function of the dielectric constant of the total fillable area.

Thus, the filling efficiency can be determined using the following equation: Filling (Ep - Epj) (1 + 2 Epj) 100% efficiency = 1 - —--------- (Ep -i- 2EpJ) (1 - Epj) 2 where Ep = dielectric constant of the fillable cross-sectional area of the cable

= dielectric constant JTiJ of the pure filler compound

Then, by measuring the change in this dielectric constant, the amount of filler compound that has been added can be determined.

12 „- _ Λ _ 68325 However, this change cannot be measured immediately, but an equation must be used that relates this change to the total change in mutual capacitance that can be measured. This equation is: ΔΕρ = ΔΕ (REp - RE + E - Ep) rMax min (Ez - REj) where: Ep = maximum value of E at 100% filling max E „= air 5¾ 1.00 min E = total dielectric constant

Ej. = dielectric constant of the conductor insulation P _ mutual capacitance without filling mutual capacitance at 100% filling

If an equation or value for Ept is placed in the above equation, it is possible to solve the filling efficiency value.

However, the first equation can be further simplified by using a certain type of cable.

As an example, when testing one type of cable in industry, such as a cable with polypropylene insulated conductors with a mutual capacitance of 52 nF / km, the equation becomes Filled ___ 1 __% = 100 50 19.4 - 0.224 efficiency 'ξΤ'Έ where ΔΕ = capacitance difference between the outer pair value or the difference between the capacitances of the inner and outer pairs (blocks 93 and 94 in Figure 6).

In the cable according to the present example, ΔΕ is limited to the range 0-16.

All of the above calculations are shown to be performed in blocks 96 and 103 of Figure 6.

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Fig. 7 is a graph illustrating the above formula for filling efficiency as a function of the percentage difference in mutual capacitance for the above-mentioned cable type.

As mentioned above, under normal operating conditions, it is assumed that the outer twisted pair 7 is 100% filled. If this is indeed the case when the slope is calculated in block 93 in Figure 6, the filling efficiency is calculated and the result of the calculation is equal to a maximum of 100% in block 6. If the result is less than a predetermined value, computer 26 feeds signals through wire pair 98 (Figure 1) to control a valve 99 to increase the pressure of the filler compound to intentionally achieve a predetermined fill state in the outer twisted pair of conductors 7. This is shown in block 101 of Figure 6. Valve 99 may be a digital flow valve such as, e.g., Model 6-607D, Digital Dynamics, Inc., Sunnyvale, California.

Further, the computer 26 may also provide a signal through the pair of wires 102 of Figure 1 to increase the temperature in the filling chamber 3 to make the filling compound less viscous. It is still possible with the computer to generate signals for the control drive means 10 via the lines 110 to change the line speed of the advancing cable 1.

It will be appreciated that computer 26 may generate signals to control one or a combination of all of the above variables as it continuously monitors relative filling efficiency.

The computer 26 also calculates the filling efficiency of the inner twisted pair 18 using the equations shown in block 103 of Figure 6. The calculated value may be different from that of the outer twisted pair 7 (block 96 in Figure 6) because the slopes may be different (see Figure 6). blocks 93 and 94).

In the event that the calculated value is found to be less than a predetermined requirement determined in block 104 of Figure 6, computer 26 generates signals to control variables, block 106 of Figure 6. These signals are similar to those generated in block 101 of Figure 6. Similarly to control filler pressure or temperature or cable 1 line speed. .

During operation of the apparatus, the computer 26 transmits signals 14 via 68325 lines 107 to cause the results of continuous filling efficiency monitoring to be stored in the storage device 108. The storage device may be a series of actual value readings in the printer with corresponding cable core lengths or record data and lengths. , which are calculated in blocks 96 and 103 of Figure 6.

Alternatively, it is possible to obtain the filling efficiency of the cable, but not as accurately as described above, by measuring the change in capacitance of one twisted pair of conductors, e.g. the change in capacitance of a pair of conductors 18. The signals describing this capacitance would be processed in the same manner as described above and placed in the computer 26. The capacitance changes of a certain type of inflatable cable would also be stored in the computer 26 and the computer would process the measured changes using blocks 93, 96, 97, 101 and 108 in Figure 6.

Claims (4)

1. A method of producing a filled, longitudinally waterproof cable, which contains one or more outer and inner pairs (7.1?) Of twine racle conductors, measuring the capacitance per unit length of an inner and outer conductor pair and determining the degree of filling of the cable by calculating on the basis of said measurement, characterized in that the capacitance measurement is performed continuously during the filling of the cable (1), that the capacitance changes in each of said conductor pairs are continuously measured and the changes are compared with a comparison signal (59, Fig. 5), calculating the relative difference in relation to the comparative value of the outer Jedar pair. (7), calculates the relative difference in capacitance of the inner conductor pair (18) compared to the relative capacitance difference of the outer conductor pair, and that the degree of filling between the outer conductor pair (7) and the inner conductor pair (18) is determined separately. on the basis of the calculated capacity differences. 2. Procedure according to. Claim 1, characterized in that control signals are formed in and for changing one or more filling parameters, such as the pressure and temperature of the filler, or the cable feed rate for control purposes, in correspondence to the differences between the measured values of the filling degree and the corresponding comparison values. Apparatus for producing a filled, longitudinally waterproof cable, said cable (1) comprising a plurality of outer and inner pairs (7, 18) of twisted conductors (7, 18), the device comprising means (9, 17) 21, 24) for measuring the capacitance per unit length of an inner and outer conductor pair, characterized by first means (9, 17) for continuously measuring the change in capacitance of an outer conductor pair (7) in the cable as this pass through the filling chamber, second means (21, 24) for continuously measuring the change in capacitance of an inner conductor pair (18) in the cable as it passes through the filling chamber, and means for said first and second means connected (77-82, 26) for generating signals indicating changes in the capacitances of the lead pair (7, 18) where changes occur.