Copper TestingCopper TestingELCM 254

©PRGodin @gmail.com

Updated Dec 2013

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Copper Cable TestingCopper Cable TestingCable 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.

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Basic Test – Visual CheckBasic Test – Visual CheckA 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.

3Stapled UTP

Basic Test – Visual CheckBasic Test – Visual CheckCheck all crimp, IDC or solder connections

visually to ensure basic installation requirements have been met, such as:

Jacket and conductor insulation properly removedNo damage to the conductorsNo 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

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Basic Test – Visual CheckBasic Test – Visual CheckMod 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 connectorBefore Crimp 5

Strain Relief

Side of MOD8 connectorAfter Crimp

Basic Test – Visual CheckBasic Test – Visual CheckConnector 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”).

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Basic Test - PhysicalBasic 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)

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Electrical and Performance TestsElectrical 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.

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Channel and Permanent Link TestChannel and Permanent Link TestThe 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.

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Permanent/Basic Link TestPermanent/Basic Link TestThe 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.

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Permanent Link TestPermanent Link Test

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Channel Link testChannel Link testChannel 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

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Channel TestChannel Test

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Image: www.mohawk-cable.com

Testing BasicsTesting 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).

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ContinuityContinuityThe 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.

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ContinuityContinuityContinuity tests are usually sufficient for:

Electrical systems Low frequency applications Shield testing

Continuity tests identify short or open circuits.

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ContinuityContinuityDiscussion: 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. :

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Wire MappingWire Mapping

The wire map is the pin-to-pin configuration of the cable. Sometimes called “Pinout”.

A Wire Map test is a continuity test.

12345678S

12345678S

Wire Map Result

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Wire Mapping ErrorsWire Mapping Errors

12345678S

12345678S

Faulty Wire Map Result

Open

Cross

Short

Miswire

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Advanced Wire MapAdvanced Wire MapSplit 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.

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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)

When a Wire Map Error isn’t an ErrorWhen a Wire Map Error isn’t an ErrorCrossover 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.

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Make sure the cable is labeled as a crossover. Typically a red or yellow tape at each end indicates a crossover cable.

DC Loop ResistanceDC Loop ResistanceResistance 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.

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DC Loop ResistanceDC Loop ResistanceResistance 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.

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deciBelsdeciBels

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.

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deciBelsdeciBels

decibels are expressed as:A ratio between input and output powerA ratio to a fixed reference:

dB for a fixed reference as 1WattdBm for a fixed reference of 1milliWatt

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LogsLogsA 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)

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dB in Data CommunicationsdB in Data CommunicationsIf 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)

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dB in Use: Power BudgetdB in Use: Power Budget

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Output InputCoupler

Output Power = 4mW10LOG(4mw/1mW)= 6 dBm

Power Loss is 25%10LOG(.75)= -1.2 dB

Power Loss is 10%10LOG(.90)= -0.4 dB

Power Loss is 50%10LOG(.50)= -3.0 dB

6 dBm

-3.0 dB-1.2 dB

-0.4 dB

6dBm + -3.0dB + -1.2dB +-0.4dB = 1.8dBm

1.8dBm

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.

dB Quick ReferencedB Quick ReferenceEvery 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)

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Attenuation or Insertion LossAttenuation or Insertion LossAttenuation 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.

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deciBels and Insertion LossdeciBels and Insertion LossInsertion 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).

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Attenuation / Insertion LossAttenuation / Insertion LossAttenuation is affected by

Length Cable construction Installation

When in use, attenuation is affected by Applied Frequency Circuit Load

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Attenuation / Insertion LossAttenuation / 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.

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Attenuation / Insertion LossAttenuation / Insertion Loss

05

101520253035

1 201 401 601 801 1001 1201 1401

db

Lo

ss

Frequency (KHz)

Attenuation

Pair 1

Pair 2

Pair 3

Pair 4

Test result from a Fluke DSP. Note the negative sign is not used for the dB values. 34

Attenuation Sample ResultsAttenuation Sample Results

Insertion Loss (dB)

Result PASS PASS PASS PASSPair Pair Pair Pair

Freq (MHz) 1,2 3,6 4,5 7,80.1 0.9 0.7 0.7 0.70.2 1 0.8 0.8 0.80.3 1.1 0.9 0.9 0.90.4 1.2 1 1 0.90.5 1.2 1.2 1.1 10.6 1.3 1.3 1.2 1.20.7 1.4 1.4 1.3 1.30.8 1.5 1.5 1.5 1.40.9 1.7 1.7 1.6 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

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Attenuation / Insertion Loss in the StandardsAttenuation / Insertion Loss in the Standards

Insertion Loss in the standards for Cat 5e

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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

decibels and Attenuationdecibels and AttenuationThe 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).

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Larger dB value = worse attenuation

Controlling AttenuationControlling AttenuationThe 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

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Attenuation Test FailureAttenuation Test FailureDiscussion: What are some likely reasons for an

attenuation test failure?

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CrosstalkCrosstalkCrosstalk 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.

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NEXT (Near End CrossTalk)NEXT (Near End CrossTalk)Transmitter and receiver placed at the same end.One pair at a time.

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PSNEXT (Power Sum Near End CrossTalk)PSNEXT (Power Sum Near End CrossTalk)

Transmitter and receiver placed at the same end.Sum of 3 pairs.

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FEXT (Far End CrossTalk)FEXT (Far End CrossTalk)

Transmitter and receiver placed at opposite ends.

One pair at a time.

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PSFEXT (Power Sum Far End CrossTalk)PSFEXT (Power Sum Far End CrossTalk)

Transmitter and receiver placed at opposite ends.

Sum of 3 pairs.

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ELFEXT (Equal Level Far End CrossTalk)ELFEXT (Equal Level Far End CrossTalk)

Accounts for attenuation effectsTransmitter and receiver placed at opposite

ends.One pair at a time.

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PSELFEXT (Power Sum Equal Level Far End CrossTalk)PSELFEXT (Power Sum Equal Level Far End CrossTalk)

Accounts for attenuation effectsTransmitter and receiver placed at opposite

ends.Sum of 3 pairs.

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CrosstalkCrosstalkThe 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.

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Crosstalk TestsCrosstalk TestsThere 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).

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(“enough data to cause Excel to gag”, based on error reports.)

decibels and Crosstalkdecibels and CrosstalkCrosstalk 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).

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Lower dB value = worse crosstalk

CrosstalkCrosstalkBecome 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).

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Crosstalk Values from the StandardsCrosstalk Values from the Standards

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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

New Additions (TIA-568C)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)

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Quick ReviewQuick ReviewAttenuation: 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.

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ACR (Attenuation to Crosstalk Ratio)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.

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ACR (Attenuation to Crosstalk Ratio)ACR (Attenuation to Crosstalk Ratio)There must be a degree of separation between

the signal and noise, known as ACR.This separation is often stated as “Headroom”.

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Frequency

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Crosstalk Attenuation

Nois

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Headro

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Sig

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ACR (Attenuation to Crosstalk Ratio)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.

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Propagation DelayPropagation DelayPropagation 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%.

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ImpedanceImpedanceAs 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.

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Signal ReflectionSignal ReflectionA 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.

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Return LossReturn LossReturn 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.

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Length MeasurementLength MeasurementCable 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.

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TDR (Time Domain Reflectometer)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).

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Test Signal

Reflections of the test signal

TDR (Time Domain Reflectometer)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.

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TDR Plot – Open CircuitTDR Plot – Open Circuit

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Imp

edance

Length

The impedance dramatically increases toward infinity, indicating an open circuit at that length.

TDR Plot – Short CircuitTDR Plot – Short Circuit

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Imp

edance

Length

The impedance dramatically decreases toward zero, indicating a short circuit at that length.

TDR Plot – Impedance ChangeTDR Plot – Impedance Change

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Imp

edance

Length

The impedance changes for part of the cable length.

TDR Plot – TerminatedTDR Plot – Terminated

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Imp

edance

Length

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 and Propagation DelayLength and Propagation DelayTo 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.

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Using the TDR measurementUsing the TDR measurementTDR (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.

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DelayDelayA 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.

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Delay SkewDelay SkewBecause 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.

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Delay SkewDelay SkewDelay 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.

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Time (ηs)

Additional TestsAdditional TestsThe following slides indicate some of the additional tests that may be performed on cable.

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Impulse NoiseImpulse NoiseMeasures alien noise induced on a cable. Some

report average noise and maximum noise spike voltage.

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Live System TestLive System TestSome 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)

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HiPot TestingHiPot TestingA 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.

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Power over Ethernet (PoE)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!

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Other TestsOther TestsCapacitance

Electrical

Specialized testers for cables that contain active or passive electronic components.

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Electrical Outlet Testers

Other Test EquipmentOther Test EquipmentThere 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

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www.fluke.com

Bit Error Rate Tester from www.tek.com

MultimeterMultimeterCurrent 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

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Butt SetButt SetTests 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.

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www.fluke.com

The butt set is either analog or digital depending on the telephone system.

Toner and Test SetToner 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

82www.amazon.com

Specialized (Basic) Cable TestersSpecialized (Basic) Cable TestersVerify 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

83www.idealindustries.ca

Specialized (Advanced) TestersSpecialized (Advanced) TestersTesters 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.

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Multiconductor Cable Tester

End of Cable TestingEnd of Cable Testing

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©PRGodin @gmail.com

Updated Dec 2013