Specifications

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. 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.
The type of AC power transformers you use to power your cameras can
contribute to Ground Loop problems. A ground can be introduced to your camera
"Capacitively" through the power transformer windings depending on the type and
construction technique used to build the AC transformer. Some transformers are
built by winding a primary (the 110 VAC side) on a metal core, then simply winding
the secondary coil (24VAC) directly over the primary coil. This puts the primary and
the secondary in direct capacitive contact. This type can cause Ground Loop
problems.
Other manufacturers build their AC transformers with a split bobbin. That is
each winding is separately mounted on the metal core. The separation of primary
and secondary coils are greatly increased, reducing the capacitive coupling and
removing the unwanted second ground in your system. This type of transformer
usually does not cost any more, and may prevent the 60 cycle ground loop from
occurring. It would help if you determine which transformers are built to minimize
capacitive coupling between windings and purchase that type only.
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.
CCTV FOCUS PROBLEM SOLVING.
Have you ever wondered why Auto Iris cameras seem to go out of focus at
night? Many installers have had to return to the job site at night and reset the focus
of a camera to solve this problem. This can be costly to your company's pocket book
and reputation. There is a solution to the problem that will enable you to set the
cameras focus correctly every time, day or night.
Let's examine what causes the Auto Iris camera to go out of focus when the
lighting level changes, as it does day to night. All lenses and Auto Iris cameras
exhibit this effect to a greater or lesser degree.
CCTV TRAINING MANUAL PAGE 5 OF 28