Sony ISSUE 3 manual Which Monitor?, Monitor sizes

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Which Monitor?

A control room operator may be required to view images on a bank of monitors for prolonged periods. As the effectiveness of the surveillance system is crucially dependent upon the degree to which the operator can remain alert and avoid fatigue, correct monitor selection is vital.

The monitor converts the video signal generated by the camera back into a visual image. It consists of a cathode ray tube (CRT) and a number of signal processing circuits.

These circuits separate the ‘luminance’ part of the signal from the ‘sync signals’. The luminance signal is routed to an amplifier, which boosts the signal to a level that can be used by the CRT. The sync signals are split onto horizontal (H) pulses and vertical (V) pulses. These in turn are amplified and modified so that they can control the vertical and horizontal deflection of the final picture.

Where the video signal is being looped through the monitor to another piece of equipment (for example, another monitor or video recorder), it is important to ensure that the system is correctly terminated. Some monitors will do this automatically, but others have a switch located at the rear. This should be set according to whether the signal is being looped out of the monitor – High Impedance – or is terminating, in which case it should set to 75 ohms.

The last item of equipment in the system should be set to 75 ohms if it does not auto terminate. Video signals usually travel over coaxial cable, which has impedance of 75 ohms. The best and most efficient transfer of the video signal from camera to monitor is when the camera, cable and monitor all have all the same impedance values. Contrast levels can be improved where a DC clamp facility is incorporated into the monitor. This can usually be selected via a switch at the rear of the unit.

Monitor sizes

Monitor size is designated by the length of a diagonal line measured from one corner of the viewing screen to the opposite corner. Thus a 9-inch monitor refers to a 9-inch diagonal picture tube. Sizes typically used in CCTV include 9, 12, 14, 17, 21 and 27 inches with different manufacturers offering different variants.

The choice of size depends in part on the distance between the viewer and monitor.

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The Sony Guide to CCTV . Issue 3

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Contents Cctv Contents Recent years Brian KellySony gives Newham a clearer picture Underground ExpandedDaewoo savings with Sony PMS Any suspicious activity on a Daewoo forecourt orFarsight Chooses HSR-1PWhat is Closed Circuit Television? When and where should it be used? Security applicationsSurveillance applications BenefitsLight SnowLight LUX DescriptionBacklight Compensation Benefits of CCD Technology Choosing aCamera Choosing a Camera SensitivityWhich lens? Colour RenditionCamera Resolution Sony ExwaveHAD CCD TechnologyDeveloped a range Selecting Correct LensFocal Length F Basic LensSelecting the Correct Lens Aperture rangeLens Format Cameras with Built-in LensWhich Monitor? Monitor sizesColour monitors Which Monitor?Monitor costs Coaxial Cables Video SignalsTransmission Transmission of Video Signals Twisted PairFibre Optics Isdn TransmissionLocalRemote Video Switching and Multiplexing SwitchersVideo Switching and Multiplexing MultiplexersHousings and Enclosures Cctv Systems ControlTelemetry DomesDigital Recording RecordingAnalogue Recording Recording Video PrintersSony Cctv Products Colour CCD CamerasSony Cctv Products Colour Video MonitorsTime-Lapse Video Recorders SVT-L230PDigital Surveillance Recorder QuadBasic Cctv Terminology APCBasic Cctv Terminology Depth of FieldMechanical Focus Sony Guide to Cctv Issue Freepost OF1503 Sony Guide to Cctv Issue CA CCTVGUIDE3