Video-accessorieshelp you save time and moneyHome > Camera Equipment > Video Accessories Video-accessories may be nice gadgets to have, but do you need them? If you thought that a home surveillance system consists only of a camera, a cable and a monitor, you are in for a surprise. Take your time to discover. What else would I need? A short list of Video-accessories would include the following:
Lenses... Infrared illuminators... They can be either mounted around the lens of special cameras, or assembled together in a common stand alone projector. The start of operation of illuminators, camera and recorder can be triggered simultaneously by a suitable motion detector. The active area can be circular or rectangular in shape, its given dimensions should be sufficient for the purpose. Illuminators are characterized by power supply (12VDC, 24 V DC or AC, or standard outlet power supply), by power consumption, by wavelength of invisible infrared radiation, by the maximum distance of effective illumination, and by the use, if only indoors or also outdoors. The 850 nm (nanometer or 10-9 meter wavelength) LEDs have longer projection range but may display a faint red hue, while the 940 nm lamps, whose range is shorter, do not. Click on Infrared Illuminators.
Alarm sensors... In one design model infrared sensors are arranged in pairs, one transmitting and one receiving from the first a beam of infrared light. The alarm is due to go off whenever reception is interrupted by a passing person or object. Passive InfraRed (PIR) (pyroelectric) sensors Video-accessories of different design use far infrared radiation to detect a small change of ambient temperature possibly generated by an intruder (or animal). Their area of detection, called sensing zone, is quite well defined, so that their number and location should be based on the actual place being monitored. An intruder entering the protected area is detected when the infrared energy emitted from his body is focused on the chip of the device. As the intruder moves, so does the hot spot on the surface of the chip. The moving hot spot causes the electronics connected to the chip to operate the relay, thereby activating the alarm on the control panel. Note that these sensors are not effective outdoors, because wind or air currents would disturb their operation. Passive sensors Video-accessories are designed to be always connected. They are able to start operation of cameras and of recorders upon being triggered. Although sometimes these definitions are blurred and overlapping, one should note that the above devices are different from motion detectors (see hereafter) that operate only when their connected camera is working. Click on Video Alarms. Motion detectors... An on-screen window defines the sensitized detection area of the screen. Front panel controls allow for vertical and horizontal sizing and positioning of the detection area. Upon detection of motion, the device provides a switch closure to start an auxiliary device such as a Time Lapse VCR (video cassette recorder). This kind of Video-accessories detectors may be useful where it is difficult to install passive sensors or cables in the monitored location. It cannot be used for many outdoor applications. Some multiplexers come with a motion detection function already included. Also motion detectors working as image processors are briefly reviewed in Video Alarms, click to see. Date and time markers... Switchers A more complex type, a sequential switcher, will also be able to switch the monitor connection from one camera to the next automatically. The dwell time, when a scene stays on the monitor before being replaced by that of the next camera, is preselectable by the operator. Only one monitor is needed for controlling many cameras, but many blind periods may conceal important views, lost in the intervals. Click on Sequential Switchers. Synchronization refers to the timing when video images are scanned. Unless multiple camera video signals are synchronized correctly, a switcher will cause some disturbances to appear on the screen at each switch over. Therefore, if using a switcher, the cameras must be synchronized, except for systems utilizing digital signal processing. Advanced and sophisticated Video-accessories solutions for image improvement and enhancement are being adopted for multi camera monitoring. They are probably reserved to public or commercial systems, so that they should not be an issue for simpler home surveillance systems. Matrix Switcher Multiplexers The larger the number of segments, the smaller each picture will be on the screen. For easier viewing a larger than usual monitor may be needed. The option is maintained to call on at request any camera for full screen display if needed, to observe actions going on. This applies to live monitoring. Multiplexers also can record all cameras in the system onto a single videotape. The cameras are recorded sequentially at a high speed rate. Most modern Video-accessories multiplexers contain a motion detection feature that enables the system to record more video frames from cameras showing motion than from those showing still views. The multiplexer selects which frames from which camera should be recorded at preference. The result is better recordings of scenes that are more likely to be useful. Click on Video Recording for details. A multi viewer (a monitor displaying many views) can also be connected to a sensor to switch the whole screen to a sensor operated single camera output. The video signal is digitally processed so that cameras need not be synchronized. When a time lapse VCR is used with a multiplexer, the recording is as fast as it can be. Special, virtual real time VCRs record four times the frames per second of conventional time lapse VCRs. During playback, the multiplexer decodes the tape allowing display of only selected frames with the same address, with considerable viewing time economy, and any desired camera can be displayed full-screen. For complex installations multiplexers offer other remarkable advantages but these should not concern us here as they are excluded from home surveillance systems because of their elevated price. Quad Splitters... Quad splitter recording yields only what appears on the monitor screen. The VCR records a four-camera display, and the playback will show the same picture. Look for Quad Splitters
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