1 cctv systems testing. 2 cctv systems cctv systems of all sizes are complex video signaling...
TRANSCRIPT
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CCTV SYSTEMS
TESTING
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CCTV SYSTEMS
CCTV systems of all sizes are complex video signaling systems, they are subject to many of the same problems found in other video applications.
CCTV systems require calibration and video signal conditioning.
There are many different types of calibration and test equipment.
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A standard video signal is always a monochrome signal.
For applications using color, the color information is overlaid on the monochrome elements to reproduce color at the monitor, recorder or printer.
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Analog video signals carry two different types of color information: Chrominance and Luminance
Luminance represents a series of voltage levels and determines the brightness of an image.
The brighter the image, the lower the amplitude of the signal.
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Chrominance signal is a sine wave.
Chrominance signal contains information representing the properties of hue and saturation for video color.
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Cameras, video recorders and monitors need periodic adjustments or calibration to maintain the correct display of chrominance and luminance signals.
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A waveform monitor is used with a color bar generator.
A waveform monitor is a special oscilloscope used to evaluate video signals.
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A waveform monitor displays the amplitude information of the signal.
A color bar generator creates an ideal color signal for measuring signal.
Color bar information is recorded for review.
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A vectorscope is another test and calibration device used for CCTV systems.
A vectorscope displays information about the chrominance, or color portion of the video signal.
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A vectorscope allows you to adjust the color by synchronizing on a subcarrier of the video signal.
The subcarrier signal information is called the color burst.
It is used to provide a synchronizing signal for representing variations in hue and saturation.
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The vectorscope is used to test three key video elements:
1. Chrominance phase.2. Gain.3. White balance.
VECTORSCOPE
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Chrominance should be in phase with the color burst.
If the chrominance is out of phase, the color hues are incorrect and causes distortions such as green faces and blue foliage.
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Gain is measured in amplitude.
It allows you to ensure that the amplitude of the signal is within acceptable thresholds.
White balancing is the process of calibrating the red, blue and green channels.
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If out of balance, the whites in the screen will be affected, this results in excessive or diminished brightness.
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When testing and calibrating equipment, make sure that each piece of equipment does not generate noise or distortion.
The calibrating equipment does affect the signal.
You will need to adjust the recorder, monitor and camera to affect the signal.
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Always start with the first piece of equipment in the circuit.
Starting from the first piece of equipment work towards the end of the circuit for proper calibration.
Adjustments to the signal must be made on the generating device.
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Calibration is the process of adjusting a measurement to a known standard and is applied at two levels.
Most pieces of equipment have controls that allow for operator adjustment.
Expert technical and electronic skills are sometimes required for serious calibration of equipment.
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Qualified service technicians in a lab environment should be used when performing these types of calibrations, they should never be performed in the field.
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As mentioned before all cameras should be tested before they are installed at their permanent location.
Final adjustments to the video images are done with the camera installed so that you can compensate for lighting, magnification and FOV.
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If the CCTV system is a CAT 5e/6 solution then the camera should be tested while plugged into a PoE switch.
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All coax cables can be quickly tested using a digital multi meter.
You will simply be testing for shorts and opens.
The next slide shows how to properly test a coax cable for shorts and opens.
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