Specifications

VIDEO LEVELS.
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.
HOW SYNC PULSE AMPLITUDE 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 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.
CCTV TRAINING MANUAL PAGE 1 OF 28