System troubleshooting

7/28/2019 System troubleshooting

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www.securitysales.com MARCH 2006B2

Part 1of 4

elcome to the latest of Security Sales & Integrations acclaimed

D.U.M.I.E.S. series: System Troubleshooting for D.U.M.I.E.S. Brought

to you by Pelco, this four-part series has been designed to help educate

readers on the fine art of video surveillance system troubleshooting. If youll recall,D.U.M.I.E.S. stands for dealers, users, managers, installers, engineers and salespeople.

This series will explain the different methods used to define, isolate and repair problem

areas found in the CCTV security arena. Some basic knowledge of simple electronic theory

will be helpful during these series of articles. However, for those who have no or limited

knowledge of electronic theory, the material will be presented in such a way as to make the

learning curve as painless as possible.

Numbers Show Cable Main Culprit

To start, lets look at a few basic statistics on the problems found in system installations.

It is a known fact that 65 percent of most problems found are associated with cabling,

connectors and connections, and cable-installation methods.

The next area, which makes up approximately 27 percent, is related to excessive inputpower, insufficient AC equipment power and an excessive temperature environment.

The last major area, at about 7 percent, is problems created by system-installation per-

sonnel, including incorrect camera setups, improper system termination and improper

By Bob Wimmer

Principal

Video Security Consultants

[email protected]

AT A GLANCE

Troubleshooting electronic sys-tems requires knowing how to

define, isolate and repair problem

areas

More than half of all systemproblems are due to issues with

cabling,cable connectors or

cable installation

Common faults include wrongtype of cable, connector errantly

installed, excessive force used

during cable pull or exceeding

cables bend radius

Best connector type is the three-piece BNC,which is the most re-

liable if it is installed correctly

In video security systems, the high-er the resistance of a single video

loop,the greater the signal loss

W

Wouldnt it be nice ifelectronic security systems

functioned trouble-freeuntil obsolescence began to

set in? As you will see, thereare too many variables forthat to happen.This series

of articles has beendesigned to help

technicians get past theirfears and master the fine

art of systemtroubleshooting.

Taming VideoSystem Trouble Spots


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setup of on-screen equipment menus.

The remaining 1 percent is due to ac-

tual equipment failures.

Key Questions for System Analysis

Troubleshooting any system is an

art form. Having the ability to ask the

right questions and then be able to re-

construct the facts can be a challenge.

Asking the right questions is critical

for good system analysis.

The first question to ask, and usu-

ally the most difficult to correctly in-

terpret the response, is: Has anyone

tried to fix this problem before me?Electronics, for the most part, are

logical in design, while most peoples

reaction to analyzing a problem is

NOT. If the answer to this question is

yes, then conducting a factory de-

fault of all associated equipment is

your first choice of action.

Remember, however, that if the

equipment offers no backup storage

method, a complete manual pro-

gramming sequence may be required

once the factory default is enabled.

Depending on the complexity of the

equipment, this could be very time-

consuming. If there is no factory de-

fault setting, another common prac-

tice is to adjust all setup and service

controls to midrange, which is usually

the starting point used by most equip-

ment manufacturers.

Once you have established that no

one tried to correct the problem before

you arr ived on the scene, the nextgroup of questions will follow the de-

tailed list at right.

Following the stated guideline that

65 percent of problems are related to

the type of cable, connectors and

cable installation methods, the next

questions should be: 2. What type of

coaxial cable was installed (material)?

3. When were the cables installed

(time)? 4. Who installed or pulled the

cables (person)?

Cabling is the lifeline for any sur-veillance system. Whether it is a stan-

dard video coaxial cable, shielded

twisted pair for data, Cat-5e for un-

shielded twisted pair (UTP) equip-

ment or Cat-5e for networking, all

must follow the guidelines set up bythis industry.

When it comes to coaxial video cable,

for many, cable is just cable. However,

this is not quite true. Although the same

number or name may refer to each type

of cable, they may use different materi-

als in their construction. It is this differ-

ence in materials that can affect the sys-

tems performance.

Baseband/Composite Vs. RF Video

In a CCTV surveillance system, thesignal transmitted by the camera

equipment is known as a basebandor

compositetype of signal. Even though

it produces a standard video signal as

found in todays non-high definition

television sets, the actual video signal

transmitted is slightly different and

causes much confusion and problems

in the security industry.

Baseband or composite video is a

raw signal consisting of video and

color information, and vertical and

horizontal synchronizing signals.

Radio frequency (RF) has all of the

same information found in a baseband

signal with one exception: It is protect-

ed by a frequency shield. This shield

protects the actual video data from out-

side sources, as well as provides a dif-

ferent means to distribute the signal.

Those differences require different

material in the cables construction.

Baseband or composite video cablerequires a center conductor made of

copper (solid or stranded), 75-ohm

impedance and an overall shield con-

structed of copper. In an RF video

cable, the center conductor is again

made of copper, and the overall im-

pedance is also 75 ohms. However,

the cables shielding is made out of

aluminum, NOT copper.

Looking at Mistake Causes, Results

The main reason for most misusesof coaxial cable is fairly simple

cost! Aluminum-shielded cable is less

expensive then cable made with cop-

per shielding. A quick comparison

shows that aluminum-shielded cable

is half the cost of copper-shielded

cable. In a large application, the cost

can be substantial.

But why is there confusion? The

most common reference for standard

coax cable is RG-59U RG stands for

radio guide; 59 indicates the imped-

ance and center conductor sizing; and

U indicates multiple uses. It does not

indicate the type of shielding used,

and this is why there is confusion.

As for the results of these errors, we

must first remember that an RF-video

signal is protected by an RF shell and,

therefore, signals, such as the vertical

Answer Me These 7 Questions

Asking the right questions is critical for good system analysis.

1. Has anyone tried to fix this problem before me?

2. What type of cabling is installed?

3. When were the cables installed?

4. Who pulled the cables?

5. How long are the cable runs?

6. Are pull boxes and/or conduits installed?

7. Are there video amplifiers in the system?


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and horizontal sync pulses, are not di-

rectly affected by the cable type.

Whereas in CCTV, being a raw videosignal, the entire signal is dependent

on the cabling material.

In a nutshell, the frequencies of ver-

tical and horizontal synchronization

are ~60Hz and ~15,750Hz, which ac-

tually places them within the audio

frequency range. The frequency range

of coax using aluminum shielding is

50MHz and greater.

This mismatch of frequency creates

problems like poor, or in some cases,

no video images. As we incorporatemore and more digital equipment into

this industry, the requirement for

more stable and distortion-free sig-

nals will become a must.

When Were the Cables Installed?

This question of when cabling was

installed may appear to be unneces-

sary, especially if you installed and are

maintaining the system. However, for

those who were not involved with the

original installation or are just enter-

ing a location for the first time, this

knowledge can save a lot of trou-

bleshooting time and effort.

If the system was just installed, a

few more questions should be consid-

ered. They are: How long are the cable

runs? Who pulled the cables?

Recommended cable lengths used in

the CCTV industry vary. The old table for

cable distance went something like this:

RG-59U............................. 1,000 feetRG-6U .............................. 1,500 feet

RG-11U ............................ 2,000 feet

These numbers do not take into

consideration how many splices (if

any) there are within the run, the

amount of looping devices in a sys-

tem and how hard the cables were

pulled during installation.

Here are a few tips for installing

coaxial cable:

First and foremost, follow all Na-

tional Electrical Code (NEC) require-ments when installing coaxial cables.

Distribute the pulling tension evenly

over the cable, and do not exceed the

minimum bend radius*. Exceeding the

maximum pulling tension or the mini-

mum bend radius of a cable can causepermanent damage, both mechanical-

ly and electrically, to the cable.

* - Bend radius = the minimum curvature

one can bend a cable without causing damage.

A single cable with shielding = 10 to 12 times

the overall cable diameter. (NEC 300.34, Con-

ductor Bending Radius)

When pulling cable through con-

duit, clean and deburr the conduit

completely and use proper lubricants

in long runs.

With more digital equipment beingincorporated in the security industry

and with this equipment requiring

higher video signal levels at the receiv-

ing end, the new recommended cable

distances read something like this:

RG-59U............................. 500 feet

RG-6U .............................. 1,000 feet

RG-11U ............................ 1,500 feetWhat does all this have to do with

troubleshooting? A great deal! The

odds are if the cable was just installed,

either the cable distance is too great,

the wrong type of cable was installed,

the connector was errantly installed,

excessive force was used during the

pulling of the cable or someone ex-

ceeded the cables bend radius. All of

these result in weak or distorted video

signals.

On the other hand, if it tur ns outthe cable has been installed for a long

period of time, the odds are there are

corrosion or moisture problems with

the cabling network. This again re-

quires more questions.


75-ohm impedance

Copper center conduction

Copper shield

CCTV only

75-ohm impedance

Copper center conduction

Aluminum shield

RF only

Comparison of Composite Vs.RF Video Cabling

Radio frequency (RF) cabling has all of the same information found in a baseband or com-

posite signal with one exception: It is protected by an aluminum frequency shield.

Problem

corrected

Problem

corrected

New

installation

Existinginstallation

Incorrect

cableExcessive

cable length

Poor

connection

installation

Corrosion Cable

breakdown

CheckCheck

Weak/Distortedvideo

Weak or Distorted Video Flowchart

Whether an installation is new or existing determines the troubleshooting strategy a

technician needs to follow.


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Are pull boxes and/or conduit in-

stalled? Are there video amplifiers

used in the system?In many applications, conduit is re-

quired to meet the local standards for

fire prevention. Many think just because

conduit is being incorporated that they

do not have to concern themselves with

special types of cable jackets or envi-

ronmental conditions, especially for

underground applications. Wrong!

It is unlikely you would ever find an

underground conduit that remains

dry for any length of time. For the

most part, within a few weeks mois-ture already surrounds the outer jack-

et of the installed cabling. With the

addition of mechanical splices within

a system, corrosion can also play a

very important part in loss of video as

well as data-signal strength.

Setting Up Testing Parameters

We now know the possible causes

of cable failures. Some will be man-

made, some due to the breakdown of

cable construction, while the corro-

sive force of moisture will lead to oth-

ers. Armed with this knowledge, we

may formally begin the troubleshoot-

ing process. But in a troubleshooting

environment, how can anyone deter-

mine the quality of the video cable in-

stalled in the system?

Any system using coaxial cable for

the video signal can be checked. Many

manufacturers offer special testing

equipment known as time domain re-flectometers (TDRs), which have been

around for many years and remain

the fastest, most accurate way to pin-

point cabling problems.

TDRs are used to locate and identify

faults in all types of coax. They can iso-

late major or minor cabling problems,

including sheath faults; broken conduc-

tors; water damage; loose connectors;

crimps; cuts; smashed cables; and short-

ed conductors and system components.

In addition, TDRs can be used totest reels of cable for shipping dam-

age, cable shortages, cable usage and

inventory management.

Principles of Operating a TDR

TDRs work on the same principle

as radar. A pulse of energy is trans-mitted down a cable, and when that

pulse reaches the end of the cable or

a fault along the way, part or all of the

pulse energy is reflected back to the

instrument. The TDR measures the

time it takes for the signal to travel

down the cable, see the problem

and reflect back. It then converts this

time to distance and displays the

information as a waveform and/or

distance reading.

The problem with TDR units is they

can be costly, varying from a few hun-

dred dollars to in excess of $1,000, de-pending on the features. For most of

us, this price usually far exceeds the

budget for the year.

The following method is a much less

expensive and simpler solution to using

a TDR. It may not pinpoint the exact

problem location, but it can get close.

The coaxial cable required in a CCTV

application is made up of a copper

center and copper shielding. All wire,

including copper, has resistance.

1. Strip cable as detailed on connector package.Place ferrule on cable jacket.

2. Solder or crimp center pin on center conductor.

4. Crimp ferrule using proper crimping tool.

3. Insert connector onto cable and slide ferruleagainst connector.

4 Steps of 3-Piece BNC Connector Assembly

1. Strip cables as detailed on connector package.

Place ferrule on cable jacket.

2. Twist connector onto center conductor.

3. Slide ferrule against connector.

4. Crimp ferrule using proper crimping tool.

4 Steps of 2-Piece BNC Connector Assembly


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Therefore, we can use this information

to check the quality of most systems.

Boning Up on Electronic Basics

In addition to wire, all components

have resistance, which is the opposite

of current. In short, the more resist-

ance you have in a circuit, the greater

the loss. In the case of a video security

system, the higher the resistance of a

single video loop, the greater the signal

loss. When this loss reaches certain lev-

els, the amount of signal left may be in-

sufficient to properly reproduce a

video image on a monitors screen.If this theory sounds a bit confusing,

lets try another way to explain resist-

ance and resistive loss in a video cable.

Take for example a standard garden

watering hose. Once connected to a

water facet, the hose acts as a pipeline to

transport the water to another location;

in this case a watering bucket. If this

same hose generates a leak, some of that

water no longer reaches the bucket. If

more and more leaks occur, eventually

little or no water will reach the bucket.

Now consider each leak in the hose

as a resistive value. The more leaks

(ohms) within a cable, the less water

(signal) will reach the bucket (monitor).

To summarize, the greater the re-

sistance found in a video cable, the

poorer the image quality. So what can

cause excessive loop resistance?

1. Exceeding normal cable distances

2. Wrong selection of video cable

3. Wrong type of shielding material4. Improper connector installation

5. Corrosion of splices within the

cable run

6. Breakdown of cable material over

time

We have already discussed most of

the problems that can cause excessive

direct current (DC) resistance in a video

system. However, there are additional

concerns that must be addressed.

The first one that comes to mind is

connectors. Are all connectors accept-able in the CCTV industry? Which con-

nectors are better? What is the proper

method for connector installation?

Using BNC Connectors for CCTV

Short for Bayonet Neill Concelman

(named after its inventors), BNC con-nectors are used with coaxial cable such

as RG-59 and RG-6 A/U. However, there

are numerous alternate definitions of

the BNC acronym, including barrel nut

connector, Bayonet nipple connector,

Bayonet navy connector, baby N con-

nector, British naval connector and

British national connector.

By any name, the basic BNC fea-

tures male-type connectors mounted

at each end of a cable. This connector

has a center pin attached to the centercable conductor and a metal tube fas-

tened to the outer cable shield. A ro-

tating ring outside the tube locks the

cable to any female connector.

The best connector type is the three-

piece BNC, which is the most reliable

if it is installed correctly. The next

connector on the list for reliability is

the two-piece BNC connector. The last

and most dangerous to any CCTV sys-

tem is the twist-on BNC connector.

Although no major equipmentmanufacturers recommend twist-on

connectors, they are nevertheless

being widely installed. The people

who use them say they are easy and

less expensive than two- or three-

piece connectors.

However, for the most part, twist-

on connectors are actually more ex-

pensive and iffy at best for perform-

ance. Studies show the normal life of a

twist-on is less than two years.

Resolving Issues With Resistance

So far, our discussion has focused

on the videos lifeline: coaxial cable.

With 65 percent of problems stem-

ming from this area, a great deal of

time was required to explain all the

relevant issues.

As mentioned, everything has re-

sistance, and we need to check the


Diagnosing a Shorted Wire

This depicts a simple test using an ohm meter to determine the overall loss of a systems

video signal due to the resistance found within the video cable structure.


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resistance value of our overall video

loop. This concept will play a very im-

portant part in our first troubleshoot-ing procedure.

Most installers rely on manufactur-

ers recommended cable distances.

But those distances are determined

only by using a high-grade, copper-

center conductor (not copper-cov-

ered steel) and do not take corrosion,

splicing, pinched cables, etc. into

consideration.

In a working system, technicians must

understand and relate to all of those

problems in order to troubleshoot andrepair any surveillance system.

The figure belowdepicts a simple

test to determine the overall loss of a

systems video signal due to the resist-

ance found within the video cable

structure. Some may term this as a

cable compliance test.

Use the following test procedure:

1. Remove the BNC connection

from the output of the camera.

2. Short the center conductor of the

cable to the shield or ground of

the connector.

3. Locate the other end of the cable

under test and remove it from the

equipment (monitor, switcher,

DVR, etc.).

4. Connect a standard ohm meter to

the circuit (black test lead to the

shield of the connector, red lead tothe center pin of the connector).

5. Check the DC resistance value on

the meter.

The maximum DC resistance

of this cable assembly should be

between 10 to 15 ohms. This indicates

the resistance loss by the cable, any

resistance loss due to connector or

splice points, and any breakdown

of the copper components of the

coaxial cable.

This is the maximum resistancethat should be between the camera

and monitoring location. If a lesser

value were found, it would be to your

advantage.

(Note: DC-resistive value has

decreased during the past few years

due to the introduction of digital

processed equipment such as multi-

plexers, DVRs and NVRs into the se-

curity industry. The main reason is

digital equipment usually requires

greater video signal strength than

analog equipment.)

With this test, installation and serv-

ice technicians will no longer have to

guess on the quality or length of the

coaxial cable of the system. This is

also especially a good reference point

if problems occur after a few months

of system operation.For the more advanced trou-

bleshooter, this test does not indicate

any system bandwidth or interference

problems. It only measures the DC-

resistance loss of the circuit.

Youre Already Halfway Home

With more than half of all problems

generated by cabling, it is a great place

to start troubleshooting. If care is

taken upon initial installation, many

of these difficulties can be avoided.The procedures described within

these pages will not always find every

problem area, but they can point serv-

ice personnel in the right direction.

Armed with an inexpensive volt-ohm

meter and some basic knowledge, sys-

tem troubleshooting can be less of a

nightmare for technicians.

Part 2 in this series will tackle the No.

1 problem confronting todays security

technicians: system termination.

Robert (Bob) Wimmer, a member ofSSI Hall ofFame, is president of Video Security Consultantsand has more than 34 years of experience in CCTV.His consulting firm is noted for technical training,system design, technical support and overall systemtroubleshooting.

Test End

Total Resistance = 10 to 15 ohms

Resistance of shield + splice + resistance of shield

Resistance of center + splice + resistance of center

Short End

Video Resistive Loss Diagram

The maximum DC resistance of the cable assembly depicted here should be between 10 to 15 ohms. This indicates the resistance loss by the

cable, any resistance loss due to connector or splice points, and any breakdown of the copper components of the coaxial cable.


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Reader Service Card No. 156

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