Transcript Copper Testing

Copper Testing
ELCM 254
©PRGodin @gmail.com
Updated Dec 2013
1
Copper Cable Testing

Cable testing is a part of the installation process.

The tests required for UTP cabling are defined in
the ANSI/TIA 568C standard.

The tests for other cables are dependent on the
manufacturer recommendations and the system
on which it is being applied.
2
Basic Test – Visual Check

A visual check is a necessary part of the
testing procedure.

Many errors that can occur during the
installation and termination process may not
be detected by electronic testing.

Installation errors cause premature cable
failures when the cables are put to use.
Stapled UTP
3
Basic Test – Visual Check

Check all crimp, IDC or solder connections
visually to ensure basic installation
requirements have been met, such as:
 Jacket and conductor insulation properly removed
◦ No damage to the conductors
◦ No risk of short circuits
 Any shields properly prepared and terminated
 Manufacturer’s installation procedures have been
followed
 Used the required tools (no damage)
 Strain relief is in place
4
Basic Test – Visual Check

Mod Plugs: Common Errors
◦ Wrong connector for conductor style
 The right contact style for stranded or solid conductors.
◦ Improperly positioned conductors
 Conductors must be all the way to the front of the
connector (copper conductor must be visible)
◦ Jacket Position
 Jacket must be clamped by the connector’s strain
relief.
Copper is
visible
Front of MOD8 connector
Before Crimp
Strain
Relief
Side of MOD8 connector
After Crimp
5
Basic Test – Visual Check

Connector Blocks and IDC
Besides aesthetics and structure, termination
blocks need to be visually checked for errors
◦ Terminated conductors must be all the way to the bottom
of the IDC’s “V” groove on both sides.
◦ Conductors must be twisted to within ½ inch of the
termination block.
◦ The conductors and insulators must not be damaged by
the termination tool or by fingernails (“shiners”).
6
Basic Test - Physical

The connectors must be firmly attached to the
cable.

Perform a pull and twist test on the connector
end.
◦ Less aggressive on MOD plugs
◦ More aggressive on Coaxial and other connectors

Do not perform pull tests on assemblies designed
without strain relief (IDC, Termination Blocks,
etc)
7
Electrical and Performance Tests

The EIA/TIA standards require specific cable
tests before the installation is considered
complete.

Once the cable passes all the tests it is
considered “certified”.

Specialized Certification testers perform all
the tests required and provide a “Pass” or
“Fail” statement.

Many of these testers have additional
features.
8
Channel and Permanent Link Test

The structured cabling installation may be tested
in 2 manners:
◦ Permanent (or Basic) Link where only the installed
“building” or permanent cable is tested.
◦ Channel Link where the installed “building” or permanent
cable, plus all the patch cords and jumpers are tested.
It tests from the user equipment at the I/O to the
equipment in the ER.
9
Permanent/Basic Link Test

The permanent or Basic link tests the
permanently installed cabling. It includes:
◦ Up to 90 m of the horizontal cable
◦ The cable between the TR and the optional consolidation
point, and from the consolidation point to the
information outlet
◦ The connection at each end of the horizontal cable

The test excludes the field test instruments cord.
10
Permanent Link Test
Image: www.mohawk-cable.com
11
Channel Link test

Channel link tests includes all the patch cords
used in the channel and includes the following
elements:
◦ Up to 90 m of the horizontal cable
◦ Cable between TR and the optional consolidation point
and from the consolidation point to the information outlet
◦ Work area patch cord
◦ Information Outlet connection (IO)
◦ Cross-Connections in the TR
◦ Patch cord or jumper wire in the TR

Note the total length of patch cords and jumper wires of the
channel must not to exceed 10m
12
Channel Test
Image: www.mohawk-cable.com
13
Testing Basics

Ensure that all proper installation and connectorization
procedures have been followed.

Never test a live system. Ensure that both ends of the
cable are disconnected before testing, otherwise system
and test equipment damage will likely occur.

Ensure the customer approves the test procedure, whether
its a Permanent Link or Channel test, and determine which
reporting documents required.

Ensure test equipment is calibrated and certified (if
required).
14
Continuity

The most basic of all the tests, the continuity
test checks for a continuous electrical path
through all the connections.

Continuity tests are often sufficient for simple,
basic cabling (provided all the connection rules
have been followed).

Basic meters and custom testers check for
continuity.
15
Continuity

Continuity tests are usually sufficient for:
◦ Electrical systems
◦ Low frequency applications
◦ Shield testing

Continuity tests identify short or open circuits.
16
Continuity

Discussion: Need access to both ends of the
cable for a continuity test but the ends are 50
meters apart.

Name 2 suggested solutions:
1.
:
2.
:
17
Wire Mapping

The wire map is the pinto-pin configuration of the
cable. Sometimes called
“Pinout”.

A Wire Map test is a
continuity test.
1
2
3
4
5
6
7
8
S
1
2
3
4
5
6
7
8
S
Wire Map Result
18
Wire Mapping Errors
Open
1
2
3
4
5
6
7
8
S
1
2
3
4
5
6
7
8
S
Cross
Short
Miswire
Faulty Wire Map Result
19
Advanced Wire Map

Split Pair errors are when a wire from a pair is
switched with a wire from another pair.

Split pair errors are critical errors. These cables
will not function for data communication
applications.

Split pairs will pass basic continuity tests but will
be identified with more advanced testers.
Split pair errors are common when dealing with cable installers that have little
experience in data communications (electricians are most likely to make this error)
20
When a Wire Map Error isn’t an Error

Crossover cables are used to connect 2 DTE
devices together without the use of a hub.

For Ethernet-based systems, crossing the pairs
for pins 1 and 2 with the pairs for 3 and 6 will
create a crossover cable (568A on one end, 568B
on the other end).

Crossover cables will indicate a wire map error
on most testers.
Make sure the cable is labeled as a crossover. Typically a red
or yellow tape at each end indicates a crossover cable.
21
DC Loop Resistance

Resistance affects the performance of the cable
by creating voltage losses for both AC and DC
signals.

Copper conductors have a predictable amount of
resistance based on conductor AWG.

Resistance is measured in Ohms (Ω). Lower
resistance is better.
22
DC Loop Resistance

Resistance measurements:
◦ Identify cable, connector and connection errors
◦ Can help identify too small an AWG

DC Loop resistance can help generalize the cable
length if the gauge is known.
 Example: If a 24AWG cable loop resistance measures
50Ω, then divide the resistance by two because a loop
resistance loops back at the end (25Ω), and look up the
resistance chart for 24 AWG.
 24AWG is about 26Ω per 1000ft, so the cable is a little
less than 1000ft.
23
deciBels

A decibel is a unit of “intensity”. It is a
logarithmic value that, in the case of electrical
testing, can represent power or voltage.

decibels are used because it is easier to add and
subtract dB values when dealing with signals that
are amplified or attenuated. The values are also
smaller and easier to deal with.
24
deciBels

decibels are expressed as:
 A ratio between input and output power
 A ratio to a fixed reference:
 dB for a fixed reference as 1Watt
 dBm for a fixed reference of 1milliWatt
25
Logs

A logarithm is a quantity representing the power
to which a fixed number (the base) must be
raised to produce a given number (source: Google Definitions)

Example:
◦ 103=1000 or Log(10)1000=3 (note the base-10 is usually omitted)
◦ This number is multiplied by 10 for power in dB
◦ (This number is multiplied by 20 for voltage in dB)

Since 100 = 1 and log(10)1=0, any ratio less than
1 will be a negative number
◦ Log(10)0.5= -0.3
◦ Multiplied by 10 for power in dB = -3dB
◦ (Multiplied by 20 for voltage in dB = -6db)
26
dB in Data Communications

If a system has an output of 20 milliWatts of power:
◦ 10LOG (POUT/1mW) = 10LOG(20) = 13dBm

If a system has an input of 6 milliWatts of power and
an output of 3 milliWatts of power
◦ 10LOG (Pout/PIN) = 10LOG(3/6) = -3dB (a Loss)

If a system amplifies a signal by 16 times the applied
signal power
◦ 10LOG (Pout/PIN) = 10LOG(16/1) = +12 dB (a Gain)
27
dB in Use: Power Budget
In this example, a transmission system is analyzed to determine if the power
received is sufficient. Note how easy it is to use dBs in this calculation.
Output Power = 4mW
10LOG(4mw/1mW)= 6 dBm
6dBm + -3.0dB + -1.2dB +-0.4dB = 1.8dBm
1.8dBm
6 dBm
Output
Input
Coupler
-3.0 dB
-0.4 dB
-1.2 dB
Power Loss is 50%
10LOG(.50)= -3.0 dB
Power Loss is 25%
10LOG(.75)= -1.2 dB
Power Loss is 10%
10LOG(.90)= -0.4 dB
28
dB Quick Reference

Every 3dB is 50% gain or loss of power
◦ Gain:
 3dB = x2 (2)
 6dB = x4 (2x2)
 9dB = x8 (2x2x2)
 12dB = x16 (2x2x2x2)
◦ Loss
 -3dB = 1/2 (1/2)
 -6dB = 1/4 (1/(2x2))
 -9dB = 1/8 (1/(2x2x2))
 -12dB = 1/16 (1/(2x2x2x2)
29
Attenuation or Insertion Loss

Attenuation is the loss of (AC) signal.

Attenuation is the sum of all losses (resistive,
capacitive and inductive).

Losses increase with an increase in frequency.

Called Insertion Loss in the latest standards,
although test equipment may still refer to it as
attenuation.
30
deciBels and Insertion Loss

Insertion loss is expressed in dB.

The standards express the Insertion Loss as the
logarithmic ratio between the output and input
voltages: 20LOG(VOUT / VIN).

Often the test equipment will report the worst
case as required by the standards (pair,
frequency and dB loss).
31
Attenuation / Insertion Loss

Attenuation is affected by
◦ Length
◦ Cable construction
◦ Installation

When in use, attenuation is affected by
◦ Applied Frequency
◦ Circuit Load
32
Attenuation / Insertion Loss

The meter and a calibrated remote unit apply test signals
on each of the pairs. The applied frequency is increased as
the transferred power is measured.

The test is performed from both ends. A “smart” remote
unit can alternately inject or measure signal. The data is
transferred from the remote to the meter using the cable
under test where it compared injected power to received
power.
33
Attenuation / Insertion Loss
db Loss
Attenuation
35
30
25
20
15
10
5
0
Pair 1
Pair 2
Pair 3
Pair 4
1
201 401 601 801 1001 1201 1401
Frequency (KHz)
Test result from a Fluke DSP. Note the
negative sign is not used for the dB values.
34
Attenuation Sample Results
Insertion Loss (dB)
Result
Freq (MHz)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
PASS
Pair
1,2
0.9
1
1.1
1.2
1.2
1.3
1.4
1.5
1.7
PASS
Pair
3,6
0.7
0.8
0.9
1
1.2
1.3
1.4
1.5
1.7
PASS
Pair
4,5
0.7
0.8
0.9
1
1.1
1.2
1.3
1.5
1.6
PASS
Pair
7,8
0.7
0.8
0.9
0.9
1
1.2
1.3
1.4
1.6
Sample of the results from a tester. Note the 100kHz steps.
Actual tests continued up to 155MHz (Cat 5e). Negative sign is omitted
35
Attenuation / Insertion Loss in the Standards

Insertion Loss in the standards for Cat 5e
Category 5e Insertion Loss
Frequency (MHz)
Channel (dB) Basic (dB)
1
2.2
2.1
4
4.5
3.9
8
6.3
5.5
10
7.1
6.2
16
9.1
7.9
20
10.2
8.9
25
11.4
10.0
31.25
12.9
11.2
62.5
18.6
16.2
100.0
24.0
21.0
36
decibels and Attenuation

The greater the difference between the output
and the input voltage the worse it is.

The dB value is expressed as an absolute value
(negative sign is dropped).
Larger dB value = worse attenuation
37
Controlling Attenuation

The specifications include physical installation
requirements in an effort to control attenuation:
◦ Use certified cable, connectors, blocks and other
components
◦ Maximum lengths for horizontal and backbone cable
◦ Maximum/minimum bend radius
 4x the cable diameter for 4 pair
 10x the outside diameter for 25 pair cable
 Follow manufacturer specifications
◦ Maximum untwisting of conductor pairs is ½ inch
◦ Maximum pull strength is 25lbs
38
Attenuation Test Failure

Discussion: What are some likely reasons for an
attenuation test failure?
39
Crosstalk

Crosstalk is the transference of signals from one
conductor pair to another. Caused by
electromagnetic induction.

Crosstalk creates “noise” on the other pairs. This
noise interferes with the data signals.

There are a variety of ways of measuring
crosstalk, as demonstrated in the following
slides.
40
NEXT (Near End CrossTalk)
Transmitter and receiver placed at the same end.
 One pair at a time.

41
PSNEXT (Power Sum Near End CrossTalk)
Transmitter and receiver placed at the same end.
 Sum of 3 pairs.

42
FEXT (Far End CrossTalk)
Transmitter and receiver placed at opposite ends.
 One pair at a time.

43
PSFEXT (Power Sum Far End CrossTalk)
Transmitter and receiver placed at opposite ends.
 Sum of 3 pairs.

44
ELFEXT (Equal Level Far End CrossTalk)
Accounts for attenuation effects
 Transmitter and receiver placed at opposite ends.
 One pair at a time.

45
PSELFEXT (Power Sum Equal Level Far End CrossTalk)
Accounts for attenuation effects
 Transmitter and receiver placed at opposite ends.
 Sum of 3 pairs.

46
Crosstalk

The standards recognize:
◦
◦
◦
◦
NEXT
ELFEXT
PSNEXT
PSELFEXT

The Equal Level tests are calculated values that
require an attenuation and a crosstalk
measurement.

NOT recognized are FEXT and PSFEXT, although
these are required to calculate the recognized
test values.
47
Crosstalk Tests
There are many individual crosstalk test results
and the test equipment creates a massive
spreadsheet.
 Consider:

◦ The Equal Level values must be calculated from
measured values.
◦ Each test includes a combination of pairs. Signal is
introduced on each of the 4 pairs and measured on each
of the remaining 3 pairs.
◦ All of these tests are performed at frequency steps up to
250 MHz.
◦ Every test must be done from each end (four tests times
two ends).
(“enough data to cause Excel to gag”, based on error reports.)
48
decibels and Crosstalk

Crosstalk is reported in dB as an absolute
(positive) value.

It represents the log of the induced signal
divided by the applied signal. (-20LOG(VInduced/VIN))

It is a ratio. The closer the ratio is to a smaller
value the worst it is (i.e. closer to 0).
Lower dB value = worse crosstalk
49
Crosstalk

Become familiar with the crosstalk results:
◦ Often the test equipment will report the worst case as
required by the standards (pair grouping, frequency and
dB crosstalk).
50
Crosstalk Values from the Standards
Category 5e NEXT
Frequency (MHz)
Channel (dB) Basic (dB)
1
60
60
4
53.5
54.8
8
48.6
50.0
10
47.0
48.5
16
43.6
45.2
20
42.0
43.7
25
40.3
42.1
31.25
38.7
40.5
62.5
33.6
35.7
100.0
30.1
32.3
51
New Additions (TIA-568C)

Cat 6a includes a test for Alien Crosstalk

Cat 6a tests to 500MHz

May support broadband video (up to 550 MHz)
52
Quick Review

Attenuation: Low values are better
◦ A lower difference between injected and measured
signals is better
◦ Remember, it is a measurement of the difference
between input and output. The lower the difference the
better the result.

Crosstalk: Higher values are better
◦ A greater difference between injected and measured
signals is better
◦ Remember, it measures the difference between the input
signal and signal seen on other pairs. The greater the
difference the better it is.
53
ACR (Attenuation to Crosstalk Ratio)

With an increase of input frequency the signal noise
increases due to crosstalk and the signal decreases
due to attenuation.

Eventually the attenuated signal and the induced
noise will be at the same intensity and it will become
impossible to differentiate between the two.
54
ACR (Attenuation to Crosstalk Ratio)
Crosstalk
Attenuation
Attn = xtalk
Signal = Noise
Noise > Signal
dB
Headroom

There must be a degree of separation between
the signal and noise, known as ACR.
This separation is often stated as “Headroom”.
Signal > Noise

Frequency
55
ACR (Attenuation to Crosstalk Ratio)

There are two ACR values:
◦ ACR utilizes the worst-case NEXT value
◦ PSACR (Power Sum ACR) uses the worst-case PSNEXT
value

The ACR and PSACR values represent the overall
performance of the cable.
56
Propagation Delay

Propagation delay is the time it takes for a signal
to travel the length of a conductor.

It is often expressed in a percentage of the
speed of light. It may also be expressed as time
(typically ηs).

Propagation Delay for UTP is approximately 68 to
72%.
57
Impedance

As previously discussed, impedance consists of
the resistance, inductance and capacitance of a
cable. It is measured in Ohms.

The cable impedance must match the circuit’s
designed impedance. In the case of UTP, the
impedance is approximately 105Ω.
58
Signal Reflection

A signal applied to a UTP cable travels the length
of the cable.

If the signal encounters a change in impedance
part of it will reflect back toward the transmitter.
The greater the change the greater the
reflection.

The signal will not reflect if it’s completely
attenuated. This occurs if the cable is too long
or if it’s properly terminated.
59
Return Loss

Return Loss occurs when a portion of the
transmitted signal is reflected back to the
transmitter. The net effect is less signal reaching
the receiving end.

Return Loss is often caused by impedance
mismatches. Some return loss is normal in a
cable.

It is a measurement required by the standards.
60
Length Measurement

Cable testers take advantage of the signal reflections
caused by impedance changes to plot the impedance of
the cable over its length.

The greater the change in impedance the greater the
reflection.

Very similar to radar where a transmitted signal is
reflected by an object. The time it takes for the signal
to return provides a distance to the object.
61
TDR (Time Domain Reflectometer)

If the propagation delay is known the tester can
accurately determine the length to the impedance
change by timing the reflections.

The tester is known as a TDR or MTDR (Metallic
Time Domain Reflectometer).
Test Signal
Reflections of the test signal
Cable under test
62
TDR (Time Domain Reflectometer)

A TDR is able to measure the length of a cable
by analysing the returning signal.
◦ If the impedance suddenly reaches toward infinity the
cable is open at that point.
◦ If the impedance suddenly reaches toward zero the cable
is shorted at that point.
63
TDR Plot – Open Circuit
Impedance
The impedance
dramatically increases
toward infinity, indicating
an open circuit at that
length.
Length
64
Impedance
TDR Plot – Short Circuit
The impedance
dramatically decreases
toward zero, indicating a
short circuit at that
length.
Length
65
TDR Plot – Impedance Change
Impedance
The impedance changes for part
of the cable length.
Length
66
TDR Plot – Terminated
Impedance
The impedance
continues toward infinity
indicating no return of
the test signal. The
cable is either
terminated, very long or
has a high attenuation.
Length
67
Length and Propagation Delay

To measure length the propagation delay must
be known. The tester uses time to plot the
reflections over distance.

Conversely, the propagation delay of a cable can
be determined if the length of the cable is know.

Most TDRs allow the user to enter the length of
the cable to determine the propagation delay.
68
Using the TDR measurement

TDR (Length) measurements are required in the
standards.

Different TDRs have different accuracy rates.
Some are accurate to within a few centimetres.
This is helpful for finding faults.

Most TDRs have a blind zone from the launch
point of the test signal. This zone varies from
tester to tester, with 1 to 3 meters as common.

TDRs can be used to measure cable remaining on
a reel.
69
Delay

A UTP cable’s twisted pairs must have different
lay lengths. Because of this each conductor pair
has a different length.

Communication systems may transmit signals
across different pairs and it is important that
these signals arrive at the destination at
approximately the same time.
70
Delay Skew

Because of the differences in lay lengths between
pairs to reduce crosstalk each conductor pair
within a cable has a different overall length.

The increased differences in lay also increase the
delay skew and can place limitation on signal
propagation.
71
Delay Skew

Delay skew measures and compares the amount
of time it takes for a signal to reach the
destination for each of the 4 pairs.

Delay Skew measurement is part of the
standards.
Time (ηs)
72
Additional Tests
The following slides indicate some of the additional
tests that may be performed on cable.
73
Impulse Noise

Measures alien noise induced on a cable. Some
report average noise and maximum noise spike
voltage.
74
Live System Test

Some devices can monitor traffic on live Ethernet
circuits.

Reports include:
◦
◦
◦
◦
◦
◦
Percent Utilization (real time)
Percent Utilization (average)
Peak Utilization
Collision (real time)
Collision (average)
Collision (peak)
75
HiPot Testing

A high voltage is applied to the conductors:
◦ Identifies near faults, such as short circuits.
◦ Identifies breakdown voltage of the wire insulation or
dielectric.
◦ Identifies foreign conductive elements such as solder
flux.
76
Power over Ethernet (PoE)

A consideration for installations is Power over
Ethernet. Wire pairs of the UTP cable are used
to transmit electrical power for such items as
wireless access points, cameras, telephones
(VoIP), etc.

The IEEE 802.3af/t address the voltage and
power standards.

The technician needs to be aware that electrical
voltage may be present on the lines. Don’t crimp
a live wire!
77

Capacitance

Electrical
www.idealindustries.ca
Other Tests
Electrical Outlet Testers

Specialized testers for cables that contain active
or passive electronic components.
78
Other Test Equipment

There are a variety of testers available to verify
the operation of a cable or connection. These
include:
◦
◦
◦
◦
◦
Multimeters (resistance, voltage, current, continuity)
Butt set (telephone connection)
Toner and test set (locate cable)
Specialized basic testers (pinout and continuity)
Specialized advanced testers and analyzers
www.fluke.com
Bit Error Rate Tester from www.tek.com
79
Multimeter

Current Measurement
◦ Used to identify current loops in shielding

Resistance & Continuity
◦ Used to verify the resistance of a terminator
◦ Can provide an approximate length of a cable if the AWG
is known
◦ Continuity
◦ Manual wire map

Voltage
◦ Set to AC may measure ambient noise
◦ Used to verify DC voltage present for VoE
80
Butt Set

Tests for a telephone tone, provides the ability to
hear any difficulties with the connection (noise,
fade, drops) and ability to connect through the
telephone circuit switch. Clips onto the wire or
switching gear.
 The butt set is either analog
or digital depending on the
telephone system.
www.fluke.com
81
Toner and Test Set

Popular tool used to locate a cable and its routing

One unit provides an electrical oscillation (tone) and the other
can pick up this tone from a short distance (inductive pickup)

Larger, higher powered units can help locate buried cables

May be used to identify the location of a break
www.amazon.com
82
Specialized (Basic) Cable Testers

Verify pin-to-pin connection
◦ Identifies shorts, opens and miswires
◦ Not capable of identifying split-pair errors

Used to test basic cables such as coaxial
connections.

Often consist of LED circuits
www.idealindustries.ca
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Testers that test the state of a specific
service connection. These include:
◦ Connectivity and performance tests
 DSL, ISDN, FR, CATV, etc…

Testers that test specific types of cable
assemblies. These may include pinout and
HiPot testing, and provide a printout of the
results.
Multiconductor
Cable Tester
www.cirris.com
84
www.gaotek.com

CATV/DTV tester
Specialized (Advanced) Testers
End of Cable Testing
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Updated Dec 2013
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