"Performance Testing" Article

"Performance Testing" Article
PERFORMANCE TESTING FOR CABLE, FIBER AND TWISTED PAIR INSTALLATION
This guide will lead you through the test procedure for verifying
operation of installed CCTV cable, twisted pair and fiber video transmission
lines. Coaxial Cable and Twisted Pair video use the same procedure to
measure the transmission capability of the video line. The fiber lines are
tested in the same way except that they may have adjustments to compensate
for video levels, we will also discuss the adjustment of those controls.
We will be testing the video lines for low frequency response and high
frequency response. The low frequency response affects the uniform
brightness of the picture and the ability of the monitor to synchronize with
the camera. The high frequency response affects picture detail sharpness and
color purity.
To test the response of your installed video cable, twisted pair or
fiber you will need a video source. You may obtain a portable battery
operated video generator or a color video camera can be used for this
purpose. The generator will be a more accurate source, but the color camera
will work for cable testing. If you use a color camera be sure to check it
for proper operation before using it for a signal source. You can test the
camera with the CM-1 CAMERA MASTER using the same testing procedure detailed
later in this section. When using the color camera the lens will be covered
by the lens cap and not removed during testing. The portable generator or
color camera is temporarily connected to the video line to test for
frequency response, and then moved to the next line for test and so on.
Use a CM-1 CAMERA MASTER test instrument to measure the frequency
response. First connect the video generator to the beginning of the video
line, where the camera will be connected.
Next go to the end of the video line and connect the CM-1 CAMERA MASTER
to the open end of the video line. Be sure to terminate the video by placing
a 75 Ohm BNC termination on the CM-1. When testing twisted pair
installations attach the video generator to the BNC video connector on the
twisted pair sender and the CM-1 to the BNC connector at the output of the
twisted pair receiver. All measurements will be made with a 75 Ohm
termination on the CM-1. You are now ready to make measurements of the video
line.
Move the selector switch on the CM-1 to the SYNC position. The display
should read 40 I.R.E. units +/- 5 I.R.E. units on short video lines, for
longer video line refer to the CABLE SLOPE LOSS IN I.R.E UNITS table. This
is the low frequency test for the video line. Next move the selector switch
to the COLOR BURST position. The display should read 40 I.R.E. units +/- 5
I.R.E. units on short video lines, for longer video line refer to the CABLE
SLOPE LOSS IN I.R.E UNITS table. This is the high frequency test. Cable
length affects the high frequency more than the low frequency. Use the table
supplied to check the video line for appropriate loss. The SYNC and COLOR
BURST should be +/- 5 I.R.E. units measured against the table of cable
length.
The next section is for the video equipment installer for measuring and
setting the CCTV equipment so that the video levels are correct.
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CCTV VIDEO TROUBLESHOOTING TIPS
Someone once said, "Knowledge is the key to success". This rule also
applies to the installation and maintenance of CCTV camera equipment. Have
you ever installed a CCTV camera system and then had to go back to solve a
problem that was overlooked. A basic understanding of CCTV video signals,
can save you hundreds of man hours, improve customer relations and increase
job profitability all at the same time. This manual will discuss problems
and solutions for CCTV camera installations.
To discuss video let's start with the unit of measure, the I.R.E. unit.
I.R.E. stands for Institute of Radio Engineers, this regulating body set the
standards of measure for the video industry. This standard has been adopted
by all industries in the United States and other parts of the world. 140
I.R.E. units are equal to 1 Volt Peak to Peak. I.R.E. units are easier to
use because they divide into a video signal evenly.
For example proper Sync level on a camera is 40 I.R.E. units, the
Voltage equivalent would be 0.2857143 Volts. Unfortunately this voltage
cannot be measured on the Volt Ohm Milliamp Meter that you use for checking
contacts. An oscilloscope has been used by some for this purpose, but it is
bulky and does not read in I.R.E. Most people would rather use the simple 40
I.R.E. units of measure.
Fortunately hand-held battery operated meters to measure the video
signal in I.R.E. units is available. This equipment is compact, extremely
accurate and simple to use. Units like the "CAMERA MASTER" can even help to
set the focus of a camera more accurately.
SYNC PULSE AMPLITUDE, HOW IT EFFECTS CCTV INSTALLATIONS.
A CCTV video camera creates synchronization pulses to lock the viewing
monitor on the picture. These pulses occur at a rate of 15,750 times a
second. There is one synchronization pulse or (sync pulse) for each line in
the picture frame. The sync pulse tells the video monitor to start drawing a
video line across the picture screen. When it gets to the end of the screen
another sync pulse begins the next line and so forth until the screen has
been filled with lines. It takes 262 and an a half lines to form a frame,
and two frames to form the video picture we see on the monitor.
The proper level for sync is 40 I.R.E. units. If the sync signal from
the camera is too small in amplitude the picture will break up or roll. If
the sync pulse is too big, any black portion of the picture will be more
gray and the dynamic range of the picture will be degraded. Peak white level
will also be compressed causing a blooming effect (loss of picture
definition).
WHITE LEVEL IRIS SETTING, HOW MUCH IS ENOUGH?
There is a standard for Iris setting, or white level and it is 100
I.R.E. units. When setting a manual iris, or an automatic iris the level
should be the same, 100 I.R.E. units.
If you set the iris below 100 I.R.E. units, the picture will be dim with
less than desired dynamic range and the white picture elements will not be
pure white. If you set the iris for more than 100 I.R.E. units, the picture
can be washed out causing loss of picture definition.
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Some cameras can be set to 120 I.R.E. units, but it should be noted
that the standard is 100 I.R.E. units and in any case all cameras in the
system should be set to the same level of white. This will ensure that the
white portion of the picture will be the same brightness when a monitor is
switched between them.
PEAK-TO-PEAK MEASUREMENT OF THE CCTV SIGNALS.
A quick measurement of the peak-to-peak video signal will re-assure you
that the CCTV camera is putting out the right level. The standard level is
140 I.R.E. units.
COLOR CAMERA'S AND WHAT IS COLOR BURST ANYWAY?
More color cameras are being used in CCTV installations. The color
camera adds a chrominance component (color information) to the signal, also
known as Chroma. This Chroma signal operates at 3.58 Mega-Hertz. The
standard level for the Chroma is 40 I.R.E. units. When the chroma level is
low, the colors will be dull. If this level is too low, the color monitor
will turn its color receiver off causing a Black and White only picture.
This condition also indicates a loss of picture detail. You can see this
effect on long cable runs.
The solution is to install a video equalizer in the line and adjust the
color burst back to 40 I.R.E. units. If the Chroma signal is too high the
picture will display color flaring and reduction of detail at the edge of
the color flare.
VERTICAL INTERVAL, ITS MANY USES
The Vertical Interval (V.I.) is the part of the video signal that tells
the monitor to start drawing a new screen. It is made up of special SYNC
pulses with no picture elements. The standard level for these SYNC pulses is
40 I.R.E. units. All video SYNC pulses should be 40 I.R.E. units. The
Vertical Interval is a very useful place to put alarm and control signals.
Some manufacturers make equipment for pan and tilt camera control, alarm
contact information, and data transmission that is inserted into the V.I.
signal and sent up or down the cable.
TERMINATION, THE END OF THE LINE.
A termination for video is a 75 Ohm resistor placed at the end of any
video cable to prevent signal reflections that cause ghosting or multiple
images on the monitor. Some CCTV equipment have built-in terminations some
of which are switch able. If you are using this equipment in series, you
must switch off all terminations except the termination at the last piece of
equipment in the cable run. Proper termination can be checked by measuring
the SYNC pulse amplitude anywhere in the video cable. It should read 40
I.R.E. with the termination ON, and 80 I.R.E. with the termination OFF. If
the SYNC level does not change when you remove the termination, the camera
or video source is not standard 75 Ohms and should be serviced or replaced.
Problems with V.I. control systems can result if the level does not double
when you remove the termination.
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THE BASIC THREE
To check performance of any CCTV camera installation make sure the SYNC
level is 40 I.R.E. units +/- 5 I.R.E... WHITE level should be 100 I.R.E.
units +/- 5 I.R.E. Remember if you want to run high white level say 120
I.R.E., be sure that all cameras in the system have the same level of I.R.E
+/- 5 I.R.E. Color burst level should be 40 I.R.E. units +/- 5 I.R.E. SYNC,
WHITE, and COLOR BURST are the three basic measurements to make to insure
proper operation of your CCTV system.
CCTV LINE-LOCK PROBLEM SOLVING TIPS
Someone once said, "Timing is everything". The same thing can be said
about Line-Lock CCTV camera installations. The Line-Lock feature is
available on most CCTV cameras, and is used to prevent picture rolling on
the monitor during switching from one camera to another. Picture Roll will
cause the loss of vital picture information in the video recorder and is
irritating to view.
The CCTV camera puts out a series of pulses called "Sync" pulses that
allow a video monitor to synchronize the picture on the screen. Special sync
pulses called "Vertical Interval Pulses" tell the monitor to begin a new
picture. The Vertical Interval Pulses from multiple cameras must be
synchronized if you wish to switch from one camera to another without the
monitor producing a picture roll. When a roll in the monitor occurs, the
Vertical Interval can be seen as a black horizontal bar that appears
momentarily on the screen.
Let’s look at how the Line-Lock system keeps CCTV cameras in
synchronism. To synchronize multiple camera's you must first have a common
reference that is all the cameras must share the same timing information.
The term Line-Lock refers to the 60 cycle AC (alternating current) supplied
by the power company. This 60 cycle line frequency is the common reference
used to lock the cameras together. For this reason only AC powered camera's
have the Line-Lock feature. DC powered camera's are not capable of being
Line-Locked.
When you select the Line-Lock feature in a camera there is internal
circuitry that samples the 60 cycle AC frequency and uses it to time the
Vertical Interval Pulses. All Line-Lock cameras’ have a Phase control that
must be adjusted when the camera is installed. The Phase control is adjusted
so that all the camera's Vertical Intervals occur at the same time.
One way to adjust this Phase control is to switch between cameras and
adjust the control until you no longer see the roll. This trial and error
method is time consuming, requires 2 installers (one at the camera and one
at the monitor) and is frustrating to accomplish. The preferred method is to
use a VTM (Video Timing Meter) to adjust the Phase control.
An oscilloscope is an instrument that displays the waveform of the
Vertical Interval Pulse. It is hard to set up, requires interpretation of
the waveform, and is bulky in size.
The VTM timing meter is specifically designed to quickly adjust the
timing error to zero with a digital readout that does not require
interpretation of the waveform.
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To make the Phase adjustment, you must select one camera as the
reference. At the monitor point connect the output of the reference camera
directly into the output of the camera that you wish to adjust, use a BNC
Barrel connector. This makes the reference signal available at the camera to
be adjusted.
Next go to the camera you wish to adjust and insert the VTM or
oscilloscope between the camera and the cable you previously connected to
the reference camera. Now adjust the camera Phase control to zero on the
meter display or zero coincidence of the Vertical Interval Pulses on the
oscilloscope. Repeat this step for each camera in the system using the same
reference camera. When all cameras in the system are adjusted, no roll of
picture will occur when you switch from one camera to another. Once the
Phase controls have been carefully set in the system no further timing
adjustments will be needed.
There is one exception. This carefully set Phase adjustment can be
upset if the power circuits are re-balanced by an electrician at the power
breaker box. When an electrician installs new power circuits into a
commercial building, sometimes they will move the circuit breakers to a
different Phase in the breaker box. In commercial buildings the utility
power is Three Phase that is three separate 60 cycle lines whose phase is
120 degrees apart. Moving the power line that your camera is on to a
different phase will throw off the timing and require a re-adjustment of the
phase control on the camera.
If monitor personnel complain about picture roll, a fast check of
timing can be made. Go to the monitor station and connect one camera as a
reference to the VTM or oscilloscope and then connect each camera one at a
time to make the measurement. The timing should be zero +/- 3 Video Lines or
Sync Pulses. A roll can be noticed if the difference between cameras is more
than a few lines. As the line difference between cameras’s increase so does
the noticeable roll. If you measure a camera and the readings seem to
change, that indicates the camera is not Line-Locked. The solution is to
select the Line-Lock feature on that camera or replace it with one that can
Line-Lock.
A clear understanding of how the Line-Lock system works combined with a
way of measuring the Phase of each camera will let you set them quickly and
correctly with confidence.
CCTV VIDEO GROUND LOOP PROBLEM SOLVING
When Video Ground Loop problems or 60 cycle Bars occur, they are easy
to see on a video monitor. They look like a horizontal band or bar across
the video monitor that slowly moves up the video screen. These bars can be
barely noticeable, or can be so bad that the video monitor loses lock and
breaks up the picture. If the video camera is Line-Locked to the 60 cycle
main power, the bars may stand still in the picture, but they still obscure
picture definition and create customer complaints.
The source of the 60 cycle bar originates from the power industries use
of local grounds to balance their power grid. Everywhere 60 cycle power is
used, a local ground is attached to the power grid to return all unbalanced
current flow to ground. As an example, you will notice that every main power
breaker box will have a ground wire or conduit going to a ground rod or
similar device connected to an earth ground. Every correctly installed power
outlet will have a connection to this ground.
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Not all grounds are created equal. In fact the earth ground in one
building is most likely to have a different voltage potential relative to
any other building, even grounds inside the same building will have
different voltages between them, based on the uneven current flow of the
power load.
Here is how the 60 cycle bar gets into your video picture. If you
connect a coaxial cable to a monitor or other equipment that plugs into the
60 cycle main power and the other end of the coaxial cable becomes grounded
locally for any reason a Ground Loop is created. Any difference in the 60
cycle voltage between these two ground points will create a current flow in
the shield of the coax that induces the 60 cycle AC voltage into your video
signal. It is easy to measure these differential voltages, simply disconnect
the video cables at the monitor point and using your voltmeter on AC volts,
measure between any two shields of the incoming video cables, you will be
amazed at the difference.
The solution is to never connect both ends of a video cable to local
grounds. Any cable can be grounded at one end without inducing the ground
loop current. When you run coax cable from one building to another, it is
acceptable to install through connection points, but do not allow the
shields to come into contact with one another or the local ground.
A coaxial connector laying in a cable tray or conduit box can
accidentally contact ground, don’t let this happen. Use tape on the
connector to prevent accidental grounding. Also try not to attach the camera
to any structure that is likely to be grounded. Remember that the camera is
already grounded at the opposite end of the coaxial cable by the monitor
equipment.
At the monitor station you may have many pieces of equipment connected
together, like a (Quad, Tape Recorder, Monitor) all of which plug into the
main 60 cycle power. This will not present a problem if you plug all of the
equipment into the same power line at the monitor point. Making sure that
all the equipment share the same ground point at the monitor station. Also
try to keep the video cables between equipment, (the service loops) as short
as possible.
If you already have an installation that has 60 cycle bars, there are
some steps you can take to solve the problem. If coaxial cable shields are
connected together anywhere in the system, separate them if possible.
Similarly remove all but one ground connection on each coaxial cable if
possible the ground is usually at the monitor end of the coaxial cable
because the monitor equipment plugs into the 60 cycle main power supply
which is grounded.
Sometimes a ground loop problem can be reduced by reversing the AC plug
on the power transformer used to power the camera, or reverse the 24 VAC
power connection to the camera. This technique will not work on DC powered
cameras.
If the problem still persists, video isolation transformers can be
installed at one end of the coaxial cable to block the shield current flow
and eliminate the 60 cycle bars. These transformers must be installed at the
coaxial cable that is originating the 60 cycle bar problem. Isolation
transformers only work when they can block the current flow in the shield.
Once 60 cycle bars become part of the video signal, no economical down
stream solution will remove the bars.
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Use a portable monitor to find the origin of the ground loop problem,
start at the camera and move down the coaxial cable until you see the bars
appear on the portable monitor. This then is the coaxial cable with the
current in the shield. Clear the ground connection or install an isolation
transformer at this point.
With an understanding of Ground Loop problems and the use of good
single ended grounding techniques, you should be able to keep the 60 cycle
bars out of your CCTV installations.
CABLE SLOPE LOSS IN I.R.E.UNITS AS MEASURED BY THE CM-2 CAMERA MASTER.
CABLE
LENGTH
IN FEET
0
50
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
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SYNC
PULSE
40
39
39
39
38
38
37
37
36
35
35
34
34
34
33
33
32
32
32
31
31
30
LUMA
WHITE
COLOR
BURST
100
99
98
98
97
97
96
96
95
93
92
92
91
91
90
90
89
89
89
88
87
87
40
37
35
34
32
31
29
27
25
23
22
20
19
18
17
16
15
14
13
12
11
10
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