"Video Trouble Shooting Tips" Article

"Video Trouble Shooting Tips" Article
CCTV VIDEO TROUBLESHOOTING TIPS
by:
Don McClatchie
FM SYSTEMS, INC.
Santa Ana, CA.
TEL: 800-235-6960
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 article 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 is 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 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 people 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 some equipment
manufacturers sell hand-held battery operated meters to measure the
video signal in I.R.E. units. This equipment is compact, extremely
accurate and simple to use. Some 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 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
from the camera is too small in amplitude the picture will
roll. If the sync pulse is too big, any black portion of
will be more gray and the dynamic range of the picture will
Peak white level will also be compressed causing a blooming
of picture definition).
cctvtips.art
sync signal
break up or
the picture
be degraded.
effect (loss
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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. 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 SIGNAL.
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 chromanance 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 are 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.
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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.
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 camera's 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.
THIS METER WILL MEASURE I.R.E. UNITS AND ALOT MORE!
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