CA2109261C - Filled copper monitoring system - Google Patents
Filled copper monitoring systemInfo
- Publication number
- CA2109261C CA2109261C CA002109261A CA2109261A CA2109261C CA 2109261 C CA2109261 C CA 2109261C CA 002109261 A CA002109261 A CA 002109261A CA 2109261 A CA2109261 A CA 2109261A CA 2109261 C CA2109261 C CA 2109261C
- Authority
- CA
- Canada
- Prior art keywords
- shield
- splice
- pass filter
- monitoring
- ground
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/58—Testing of lines, cables or conductors
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
An apparatus and a method are disclosed for monitoring electrical cables for the presence of moisture along the cable. The cable is of the type having copper conductors and a metallic shield. The shield is grounded through shield ground units including high pass filters and band pass filters. The band pass filters ground induced AC currents at the local power line frequency, while the high pass filter grounds voice frequency currents from power line harmonics, electric motors and other noise sources. The splices in the system are monitored by splice sensors communicating with the monitoring unit over a twisted pair of the cable.
Description
~10~2~'1 FIELD OF THE INVENTION
The present invention relates to the monitoring of communication cables for moisture penetration.
BACKGROUND
Telephone and other communication cables are subject to damage and wear from environmental conditions and man made causes.
Severe weather conditions such as high winds, snow, icing, rain, floods, and lightning can damage exposed cables. Damage can occur from nearby construction or by vandalism. The ingress of rain or ground water into cable cores or splice closures at damage locations is a major cause of outages. Every effort is made to keep the cable in good repair and water out of the cable structure.
Plastic or paper insulated copper conductor communication cables are particularly susceptible to damage and failure when water enters the cable structure or a splice closure. Water shorts the conductors, disrupting service and causing rapid electrolysis corrosion. To inhibit water penetration, modern telephone cables are often filed with water blocking compounds. While providing good resistance to water damage, the filling compounds do not provide complete invulnerability from water caused damage. Cable splice locations are particularly susceptible. In splice intensive distribution networks, splice closures are often reentered to add or rearrange service to businesses and residential customers. The closing and 210926~
sealing of the splice closure is subject to wear and tear with the risk of failure increasing on each occasion.
Maintenance monitoring systems have been used to detect and provide early warning of cable trouble. For filled telephone cables, an electronic system was developed as described in McNaughton et al. United States patent 4,480,251, issued October 30, 1984. This early system used specially designed moisture detection conductors which were an integral part of the cable construction. Another system, described in Vokey and Sontag United States Patent 5,077,526 issued December 31, 1991, uses the armor on a fiber optic cable in a ground return configuration with splice moisture sensors connected to the armor and a local ground.
Modern copper telephone cables, filled with water blocking compounds, are in popular use for all telephone applications. These plastic insulated copper conductor cables are constructed with an overall aluminum shield and outer plastic jacket. The standard practice is to ground the shield at the cable ends and at a fixed intervals along the cable length. The grounding provides a path to earth for foreign voltages and currents induced or conducted from power lines or lightning. The ground path also provides an important low impedance path for voice frequency noise currents which are caused by power line harmonics. Shunting to ground of the voice frequency noise reduces the noise interference on the copper pair circuits.
~ 2109~61 The special moisture conductors to monitor the cable core along the cable length, as described by McNaughton et al are not included in standard telephone cables. The grounding requirement prevents using the monitoring method described by Vokey and Sontag, which requires transmission of the sensor signals over the monitored cable armor.
The present invention overcomes or ameliorates the limitations of the prior art to provide monitoring of the outer cable shield, plastic jacketand splice closures while maintaining the grounding on the cable shield.
SUMMARY
According to one aspect of the present invention there is provided a method of monitoring for moisture penetration a cable of the type having a metallic shield covered by a dielectric jacket, said method comprising:
grounding the shield at spaced positions therealong through a band pass filters having a pass frequency substantially equal to local main power;
grounding the shield at spaced positions therealong through a high pass filter;
applying DC monitoring signal to the shield; and monitoring the DC current on the shield.
By grounding the cable shield through the two filters, both power line and voice frequency currents are grounded. At the same time a DC current on the shield will be grounded only by a fault.
According to another aspect of the present invention there is provided a shield ground unit for grounding a metallic shield of a communications table, comprising high pass filter means for passing voice frequency noise currents and band pass filter means connected parallel to the high pass filter means for passing power line frequency currents.
The shield ground unit may be connected to the shield and to ground at desired locations along the cable to provide the desired grounding of induced currents.
According to another aspect of the present invention there is provided a method of monitoring communications cable of the type having at least one pair of conductors extending therealong, an electrically conductive, protective shield, a dielectric jacket covering the shield and one or more splices in the cable, said method comprising:
monitoring each splice for moisture penetration;
generating a splice signal in response to the detection of moisture penetration at a splice;
applying the splice signal to the pair of conductors;
grounding alternating currents in the shield through a high pass filter;
~109261 applying a direct current signal to the shield;
monitoring the pair of conductors for a splice signal; and monitoring the current magnitude of the direct current signal on the shield.
Two separate monitoring paths are used. The first path uses a single pair from the cable core to monitor the individual splices. Splice sensors, which are placed in monitored splice closures, are connected in parallel across the monitoring pair. The second path uses the cable shield as the monitoring sensor and the communications path. Grounding filters ground the noise frequencies of concern, while allowing the maintenance of the DC signal on the shield. The two separate paths are preferably combined at the monitoring end of the cable and are connected to a single monitoring circuit.
According to a further aspect of the present invention there is provided a system for monitoring for moisture penetration a communications cable system including cable of the type having at least one electrically conductive pair therealong, an electrically conductive shield, a dielectric jacket covering the shield and one or more splices in the system, said system comprising:
splice sensor means associated with each splice for detecting the penetration of moisture into the splice and for generating an ~ 21092~ 1 electrical splice signal in response thereto, the splice sensor means being coupled to the conductor pair for delivering the signal thereto;
shield ground means connecting the shield to the ground for grounding alternating currents induced in the shield;
power supply means for applying a direct current signal to the shield; and monitoring means for monitoring the conductor pair for splice signals and the shield for leakage currents.
The shield is preferably grounded through a unit that includes a grounding capacitor, a tuned grounding filter and an over voltage surge arrestor, which form a unique circuit that provides AC grounding for power line frequency and voice frequency noise currents, and high current surge protection while allowing a low voltage DC monitoring current.
The shield monitoring path is preferably connected to the splice sensor path through a current limiting resistor to isolate sensor pulses from the low impedance path to ground.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:
Figure 1 is a schematic view of the monitoring system;
Figure 2 is a schematic of a shield ground unit;
2109~Sl Figure 3 is a graph illustrating the impedance versus frequency characteristics of the shield ground unit;
Figure 4 is a schematic showing the placement of shield ground units and splice sensor units along a cable route; and Figure 5 is a schematic of a splice and sensor unit connection to the system.
DETAILED DESCRIPTION
Referring to the accompanying drawings, and particularly to Figure 1, there is illustrated a conventional communications cable 10 with an outer dielectric, waterproof jacket 12 covering an aluminum shield 14.
Within the shield is the cable core 16 consisting of multiple copper conductors arranged in twisted pairs. One of these pairs 18 is used as described in the following for communication with splice sensors in the system.
A DC power source 20 has a negative terminal 22 connected to one of the conductors of the pair 18 and a positive terminal 24 connected through a resistance R1 to the ground. The positive terminal is also connected to a low pass filter 28 which is in turn connected to the negative terminal of an amplifier 30. The output of amplifier 30 is delivered to a monitor 31.
21~926~
The negative terminal of the power source 20 is connected to a current limiting resistor R2 that is in its turn connected to shield 14 which isgrounded through a shield ground unit 34.
As illustrated in Figures 1 and 2, the shield ground unit includes a high pass filter 36 constituted by a capacitor C1. Connected in parallel with the capacitor C1 is a band pass filter 40 that is a series resonant filter composed of inductor L1 and capacitor C2. Also connected in parallel with capacitor C1 and series resonant filter 40 is a surge arrestor 46. This is a gas discharge tube G1.
The capacitor C1 provides a low impedance ground for voice frequency noise currents induced on the shield. The series resonant filter consisting of inductor L1 and capacitor C2 exhibits very low impedance at the resonant frequency. The values of the inductor and the capacitor are calculated by:
Fc = 1 /(2xrIx~(L1 xC2) where Fc is the frequency.
The values of L1 and C2 are chosen to resonate the filter 40 at the power line frequency, which is 60 Hz in North America and 50 Hz in Europe and Asia. The filter 40 provides a low impedance path to ground for currents induced by AC power, while blocking the low voltage DC
monitoring signal.
~ 210~,~61 The grounding capacitor C1 is selected to provide a low impedance path to ground for all frequencies above 300 HZ while blocking the DC monitoring current. This AC path to ground through capacitor C1 improves the effectiveness of the aluminum shield in minimizing voice frequency noise interference from power line harmonics, electric motors and other noise sources.
A typical impedance versus frequency curve for the shield ground unit 34 is shown in Figure 3. The filter appears as an open circuit for DC currents, a low resistance path of 25 ohms or less at power line frequencies and as a 25 ohms or less impedance at frequencies above 300 Hz.
The surge arrestor 46 provides overvoltage and lighting surge protection. The gas tube G1 is normally an open circuit. AC voltages and currents or lighting surges which exceed the handling capacity of the series resonant circuit 40 or the filter capacitor C1 will cause the gas in the tube to ionize and form a very low resistance path to the ground. This will safely shunt the foreign currents to earth. When the surge current ends, the gas tube deionizes and returns to a normal nonconducting state.
As shown in Figure 4, shield ground units 34 are used in several places along the cable where normal grounding is required. In addition, splice sensor units 50 are used at all splice locations to monitor forwater penetration into a splice enclosure. As illustrated in Figure 5, the unit l4_ 50 includes a sensor 52 connected to a moisture detection tape 54 that is wrapped around the splice bundle. When water contacts the tape, the remote sensor is triggered to transmit a digitaily encoded alarm signal through the conductor pair 18 to a monitor schematically illustrated at 31 in Figure 1. The sensor is powered by the DC voltage applied to the conductor pair 18 by the power source 20.
Each sensor 52 generates a unique coded signal so that the location of a leak can be determined immediately from the code transmitted.
The resistor R2 connected in series between the power source 20 and the cable shield 14 provides a current limiting path for the DC
monitoring signal to the shield and isolates the sensor pulse signals from the low impedance path to ground through capacitor C1 and series resonant circuit 40. This ensures that pulse signals from the sensors will be detected even if the monitor shield has a low resistance fault or is shorted to ground.
The splice sensor units may include remote disconnect units 56 that may be activated by a signal placed on the conductor pair 18 to disconnect the electric couplings between the cable shields at a splice or branch. This enables the identification of a faulted section of cable, even where the cable highly branched. An appropriate splice sensor is described in United States Patent 4,480,251, to which the reader may refer for a complete description.
,~
~ - 11 - 21~92~
While one particular embodiment of the present invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. The scope of the invention is to be ascertained solely by reference to the accompanying claims.
The present invention relates to the monitoring of communication cables for moisture penetration.
BACKGROUND
Telephone and other communication cables are subject to damage and wear from environmental conditions and man made causes.
Severe weather conditions such as high winds, snow, icing, rain, floods, and lightning can damage exposed cables. Damage can occur from nearby construction or by vandalism. The ingress of rain or ground water into cable cores or splice closures at damage locations is a major cause of outages. Every effort is made to keep the cable in good repair and water out of the cable structure.
Plastic or paper insulated copper conductor communication cables are particularly susceptible to damage and failure when water enters the cable structure or a splice closure. Water shorts the conductors, disrupting service and causing rapid electrolysis corrosion. To inhibit water penetration, modern telephone cables are often filed with water blocking compounds. While providing good resistance to water damage, the filling compounds do not provide complete invulnerability from water caused damage. Cable splice locations are particularly susceptible. In splice intensive distribution networks, splice closures are often reentered to add or rearrange service to businesses and residential customers. The closing and 210926~
sealing of the splice closure is subject to wear and tear with the risk of failure increasing on each occasion.
Maintenance monitoring systems have been used to detect and provide early warning of cable trouble. For filled telephone cables, an electronic system was developed as described in McNaughton et al. United States patent 4,480,251, issued October 30, 1984. This early system used specially designed moisture detection conductors which were an integral part of the cable construction. Another system, described in Vokey and Sontag United States Patent 5,077,526 issued December 31, 1991, uses the armor on a fiber optic cable in a ground return configuration with splice moisture sensors connected to the armor and a local ground.
Modern copper telephone cables, filled with water blocking compounds, are in popular use for all telephone applications. These plastic insulated copper conductor cables are constructed with an overall aluminum shield and outer plastic jacket. The standard practice is to ground the shield at the cable ends and at a fixed intervals along the cable length. The grounding provides a path to earth for foreign voltages and currents induced or conducted from power lines or lightning. The ground path also provides an important low impedance path for voice frequency noise currents which are caused by power line harmonics. Shunting to ground of the voice frequency noise reduces the noise interference on the copper pair circuits.
~ 2109~61 The special moisture conductors to monitor the cable core along the cable length, as described by McNaughton et al are not included in standard telephone cables. The grounding requirement prevents using the monitoring method described by Vokey and Sontag, which requires transmission of the sensor signals over the monitored cable armor.
The present invention overcomes or ameliorates the limitations of the prior art to provide monitoring of the outer cable shield, plastic jacketand splice closures while maintaining the grounding on the cable shield.
SUMMARY
According to one aspect of the present invention there is provided a method of monitoring for moisture penetration a cable of the type having a metallic shield covered by a dielectric jacket, said method comprising:
grounding the shield at spaced positions therealong through a band pass filters having a pass frequency substantially equal to local main power;
grounding the shield at spaced positions therealong through a high pass filter;
applying DC monitoring signal to the shield; and monitoring the DC current on the shield.
By grounding the cable shield through the two filters, both power line and voice frequency currents are grounded. At the same time a DC current on the shield will be grounded only by a fault.
According to another aspect of the present invention there is provided a shield ground unit for grounding a metallic shield of a communications table, comprising high pass filter means for passing voice frequency noise currents and band pass filter means connected parallel to the high pass filter means for passing power line frequency currents.
The shield ground unit may be connected to the shield and to ground at desired locations along the cable to provide the desired grounding of induced currents.
According to another aspect of the present invention there is provided a method of monitoring communications cable of the type having at least one pair of conductors extending therealong, an electrically conductive, protective shield, a dielectric jacket covering the shield and one or more splices in the cable, said method comprising:
monitoring each splice for moisture penetration;
generating a splice signal in response to the detection of moisture penetration at a splice;
applying the splice signal to the pair of conductors;
grounding alternating currents in the shield through a high pass filter;
~109261 applying a direct current signal to the shield;
monitoring the pair of conductors for a splice signal; and monitoring the current magnitude of the direct current signal on the shield.
Two separate monitoring paths are used. The first path uses a single pair from the cable core to monitor the individual splices. Splice sensors, which are placed in monitored splice closures, are connected in parallel across the monitoring pair. The second path uses the cable shield as the monitoring sensor and the communications path. Grounding filters ground the noise frequencies of concern, while allowing the maintenance of the DC signal on the shield. The two separate paths are preferably combined at the monitoring end of the cable and are connected to a single monitoring circuit.
According to a further aspect of the present invention there is provided a system for monitoring for moisture penetration a communications cable system including cable of the type having at least one electrically conductive pair therealong, an electrically conductive shield, a dielectric jacket covering the shield and one or more splices in the system, said system comprising:
splice sensor means associated with each splice for detecting the penetration of moisture into the splice and for generating an ~ 21092~ 1 electrical splice signal in response thereto, the splice sensor means being coupled to the conductor pair for delivering the signal thereto;
shield ground means connecting the shield to the ground for grounding alternating currents induced in the shield;
power supply means for applying a direct current signal to the shield; and monitoring means for monitoring the conductor pair for splice signals and the shield for leakage currents.
The shield is preferably grounded through a unit that includes a grounding capacitor, a tuned grounding filter and an over voltage surge arrestor, which form a unique circuit that provides AC grounding for power line frequency and voice frequency noise currents, and high current surge protection while allowing a low voltage DC monitoring current.
The shield monitoring path is preferably connected to the splice sensor path through a current limiting resistor to isolate sensor pulses from the low impedance path to ground.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:
Figure 1 is a schematic view of the monitoring system;
Figure 2 is a schematic of a shield ground unit;
2109~Sl Figure 3 is a graph illustrating the impedance versus frequency characteristics of the shield ground unit;
Figure 4 is a schematic showing the placement of shield ground units and splice sensor units along a cable route; and Figure 5 is a schematic of a splice and sensor unit connection to the system.
DETAILED DESCRIPTION
Referring to the accompanying drawings, and particularly to Figure 1, there is illustrated a conventional communications cable 10 with an outer dielectric, waterproof jacket 12 covering an aluminum shield 14.
Within the shield is the cable core 16 consisting of multiple copper conductors arranged in twisted pairs. One of these pairs 18 is used as described in the following for communication with splice sensors in the system.
A DC power source 20 has a negative terminal 22 connected to one of the conductors of the pair 18 and a positive terminal 24 connected through a resistance R1 to the ground. The positive terminal is also connected to a low pass filter 28 which is in turn connected to the negative terminal of an amplifier 30. The output of amplifier 30 is delivered to a monitor 31.
21~926~
The negative terminal of the power source 20 is connected to a current limiting resistor R2 that is in its turn connected to shield 14 which isgrounded through a shield ground unit 34.
As illustrated in Figures 1 and 2, the shield ground unit includes a high pass filter 36 constituted by a capacitor C1. Connected in parallel with the capacitor C1 is a band pass filter 40 that is a series resonant filter composed of inductor L1 and capacitor C2. Also connected in parallel with capacitor C1 and series resonant filter 40 is a surge arrestor 46. This is a gas discharge tube G1.
The capacitor C1 provides a low impedance ground for voice frequency noise currents induced on the shield. The series resonant filter consisting of inductor L1 and capacitor C2 exhibits very low impedance at the resonant frequency. The values of the inductor and the capacitor are calculated by:
Fc = 1 /(2xrIx~(L1 xC2) where Fc is the frequency.
The values of L1 and C2 are chosen to resonate the filter 40 at the power line frequency, which is 60 Hz in North America and 50 Hz in Europe and Asia. The filter 40 provides a low impedance path to ground for currents induced by AC power, while blocking the low voltage DC
monitoring signal.
~ 210~,~61 The grounding capacitor C1 is selected to provide a low impedance path to ground for all frequencies above 300 HZ while blocking the DC monitoring current. This AC path to ground through capacitor C1 improves the effectiveness of the aluminum shield in minimizing voice frequency noise interference from power line harmonics, electric motors and other noise sources.
A typical impedance versus frequency curve for the shield ground unit 34 is shown in Figure 3. The filter appears as an open circuit for DC currents, a low resistance path of 25 ohms or less at power line frequencies and as a 25 ohms or less impedance at frequencies above 300 Hz.
The surge arrestor 46 provides overvoltage and lighting surge protection. The gas tube G1 is normally an open circuit. AC voltages and currents or lighting surges which exceed the handling capacity of the series resonant circuit 40 or the filter capacitor C1 will cause the gas in the tube to ionize and form a very low resistance path to the ground. This will safely shunt the foreign currents to earth. When the surge current ends, the gas tube deionizes and returns to a normal nonconducting state.
As shown in Figure 4, shield ground units 34 are used in several places along the cable where normal grounding is required. In addition, splice sensor units 50 are used at all splice locations to monitor forwater penetration into a splice enclosure. As illustrated in Figure 5, the unit l4_ 50 includes a sensor 52 connected to a moisture detection tape 54 that is wrapped around the splice bundle. When water contacts the tape, the remote sensor is triggered to transmit a digitaily encoded alarm signal through the conductor pair 18 to a monitor schematically illustrated at 31 in Figure 1. The sensor is powered by the DC voltage applied to the conductor pair 18 by the power source 20.
Each sensor 52 generates a unique coded signal so that the location of a leak can be determined immediately from the code transmitted.
The resistor R2 connected in series between the power source 20 and the cable shield 14 provides a current limiting path for the DC
monitoring signal to the shield and isolates the sensor pulse signals from the low impedance path to ground through capacitor C1 and series resonant circuit 40. This ensures that pulse signals from the sensors will be detected even if the monitor shield has a low resistance fault or is shorted to ground.
The splice sensor units may include remote disconnect units 56 that may be activated by a signal placed on the conductor pair 18 to disconnect the electric couplings between the cable shields at a splice or branch. This enables the identification of a faulted section of cable, even where the cable highly branched. An appropriate splice sensor is described in United States Patent 4,480,251, to which the reader may refer for a complete description.
,~
~ - 11 - 21~92~
While one particular embodiment of the present invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. The scope of the invention is to be ascertained solely by reference to the accompanying claims.
Claims (20)
1. A method of monitoring communications cable of the type having at least one pair of conductors extending therealong, an electrically conductive, protective shield, a dielectric jacket covering the shield and one or more splices in the cable, said method comprising:
monitoring each splice for moisture penetration;
generating a splice signal in response to the detection of moisture penetration at a splice;
applying the splice signal to the pair of conductors;
grounding alternating currents in the shield through a high pass filter;
applying a direct current signal to the shield;
monitoring the pair of conductors for a splice signal; and monitoring the current magnitude of the direct current signal on the shield.
monitoring each splice for moisture penetration;
generating a splice signal in response to the detection of moisture penetration at a splice;
applying the splice signal to the pair of conductors;
grounding alternating currents in the shield through a high pass filter;
applying a direct current signal to the shield;
monitoring the pair of conductors for a splice signal; and monitoring the current magnitude of the direct current signal on the shield.
2. A method according to Claim 1 further comprising combining the splice signals with the direct current signals to provide a combined signal and monitoring the combined signal.
3. A method according to Claim 1 wherein the grounding step further comprises grounding the shield through a band pass filter having a pass frequency substantially equal to the frequency of local mains power.
4. A system for monitoring for moisture penetration a communications cable system including cable of the type having at least one electrically conductive pair therealong, an electrically conductive shield, a dielectric jacket covering the shield and one or more splices in the system, said system comprising:
splice sensor means associated with each splice for detecting the penetration of moisture into the splice and for generating an electrical splice signal in response thereto, the splice sensor means being coupled to the conductor pair for delivering the signal thereto;
shield ground means connecting the shield to the ground for grounding alternating currents induced in the shield;
power supply means for applying a direct current signal to the shield; and monitoring means for monitoring the conductor pair for splice signals and the shield for leakage currents.
splice sensor means associated with each splice for detecting the penetration of moisture into the splice and for generating an electrical splice signal in response thereto, the splice sensor means being coupled to the conductor pair for delivering the signal thereto;
shield ground means connecting the shield to the ground for grounding alternating currents induced in the shield;
power supply means for applying a direct current signal to the shield; and monitoring means for monitoring the conductor pair for splice signals and the shield for leakage currents.
5. A system according to Claim 4 wherein the splice sensor means comprise means for generating a pulsed, coded splice signal.
6. A system according to Claim 4 wherein the shield ground means comprise a high pass filter.
7. A system according to Claim 6 wherein the high-pass filter comprises a capacitor.
8. A system according to Claim 6 wherein the shield ground means further comprises a band pass filter.
9. A system according to Claim 7 wherein the shield ground means further comprises a band pass filter comprising an inductor and a capacitor connected in series.
10. A system according to Claim 8 wherein the band pass filter passes alternating currents at the local mains power frequency.
11. A system according to Claim 9 wherein the band pass filter passes alternating currents at the local mains power frequency.
12. A system according to any one of Claims 6 through 11 wherein the shield ground means comprise surge arrestor means for shorting to ground surge voltages on the shield in excess of a predetermined voltage.
13. A system according to Claim 12 including a plurality of shield ground units connecting the shield to ground at spaced locations along the cable.
14. A system according to Claim 4 wherein the power supply means comprise a direct current power supply connected to the conductor pair and to the shield through a current limiting resistor.
15. A shield ground unit for grounding a metallic shield of a communications table, comprising high pass filter means for passing voice frequency noise currents and band pass filter means connected parallel to the high pass filter means for passing power line frequency currents.
16. A unit according to Claim 15 further comprising surge arrestor means connected in parallel to the high pass filter means and the band pass filter means for shorting to ground surge voltages in excess of a predetermined voltage.
17. A unit according to Claim 16 wherein the high pass filter means comprise a capacitor.
18. A unit according to Claim 17 wherein the band pass filter means comprise an inductive-capacitive series filter.
19. A unit according to Claim 18 wherein the surge arrestor comprises a gas discharge tube arrestor.
20. A method of monitoring for moisture penetration a cable of the type having a metallic shield covered by a dielectric jacket, said method comprising:
grounding the shield at spaced positions therealong through a band pass filters having a pass frequency substantially equal to local main power;
grounding the shield at spaced positions therealong through a high pass filter;
applying DC monitoring signal to the shield; and monitoring the DC current on the shield.
grounding the shield at spaced positions therealong through a band pass filters having a pass frequency substantially equal to local main power;
grounding the shield at spaced positions therealong through a high pass filter;
applying DC monitoring signal to the shield; and monitoring the DC current on the shield.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002109261A CA2109261C (en) | 1993-10-26 | 1993-10-26 | Filled copper monitoring system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002109261A CA2109261C (en) | 1993-10-26 | 1993-10-26 | Filled copper monitoring system |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2109261A1 CA2109261A1 (en) | 1995-04-27 |
| CA2109261C true CA2109261C (en) | 1999-03-16 |
Family
ID=4152488
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002109261A Expired - Lifetime CA2109261C (en) | 1993-10-26 | 1993-10-26 | Filled copper monitoring system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2109261C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105043959A (en) * | 2015-07-10 | 2015-11-11 | 山东省纺织科学研究院 | Chemical liquid permeability test apparatus |
-
1993
- 1993-10-26 CA CA002109261A patent/CA2109261C/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105043959A (en) * | 2015-07-10 | 2015-11-11 | 山东省纺织科学研究院 | Chemical liquid permeability test apparatus |
| CN105043959B (en) * | 2015-07-10 | 2017-12-01 | 山东省纺织科学研究院 | A kind of chemical liquid permeance property test instrument |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2109261A1 (en) | 1995-04-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20131028 |