CCTV SYSTEMS TESTING
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.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • Chrominance signal is a sine wave. • Chrominance signal contains information representing the properties of hue and saturation for video color.
CCTV SYSTEMS • Cameras, video recorders and monitors need periodic adjustments or calibration to maintain the correct display of chrominance and luminance signals.
CCTV SYSTEMS • A waveform monitor is used with a color bar generator. • A waveform monitor is a special oscilloscope used to evaluate video signals.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • The vectorscope is used to test three key video elements: • Chrominance phase. • Gain. • White balance. VECTORSCOPE
CCTV SYSTEMS • 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.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • If out of balance, the whites in the screen will be affected, this results in excessive or diminished brightness.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • Qualified service technicians in a lab environment should be used when performing these types of calibrations, they should never be performed in the field.
CCTV SYSTEMS • 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.
CCTV SYSTEMS • If the CCTV system is a CAT 5e/6 solution then the camera should be tested while plugged into a PoE switch.
CCTV SYSTEMS • 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.