Specifications

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) or an
oscilloscope 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.
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.
CCTV TRAINING MANUAL PAGE 17 OF 28