CCTV systems can be extremely simple: a camera with lens, with cable running to a monitor. Some systems can be very complex, using all manner of bang-up-to-date technological wonders.
Nonetheless, all of them can be broken down into three basic parts:
1. ‘Take pictures’ with a video camera,
2. Send the pictures to their destinations,
3. Manage the pictures that arrive there.
I’m sure you’ll agree that tackling this subject as three ‘bites’ makes any size of CCTV system in Georgina easier to digest. So let’s look at each one in turn and point you to the bits that can get the job done for you.
1. Take pictures with a video camera
Otherwise known as ‘image acquisition’ if you want to sound like a proper consultant! Start with the basic camera. It carries a chip at the front that gives an electrical signal when hit by light or infrared. The other 99% of the camera is there to control the video pictures that emerge out of the back. We’ll deal with that output signal in a short while. Before then, add a lens to the camera or there will not be a focused image. Choose the focal length of the lens (given in millimetres) so that the field-of-view suits your scene and gives you the level of detail you need. You can look back at the previous article where we discussed this ‘Operational Requirement’ in greater detail. To create pictures one more thing is essential. Actually, trillions of things. Photons – appearing as light or infrared. There are no decent pictures without sufficient light. This is so commonly overlooked in CCTV. Don’t make such a mistake.
Having completed these fundamental steps, what is going to protect the camera and lens from dirt, weather, etc? Put them in a protective housing. What will keep this box of tricks pointing at the right scene? Simplest example is a wall bracket including a manually adjustable joint that keeps your static camera oriented correctly come rain or shine. If you need to remotely control its orientation then add a motorized pan and tilt unit between the mounting and camera. The pan/tilt (and any zoom lens on the camera) will need to decode remote control signals, so a ‘telemetry’ receiver is needed too. For many years combinations of all five items can come in the form of PTZ dome units, so, why ever use rectangular ‘shoebox’ camera assemblies? Because attaching high power lamps and ‘windscreen wipers’ is much easier, and you can choose almost any camera and much better lenses to produce your pictures.
Totting up to a heavy load, sturdy mounts are needed, for instance, purpose-built poles or lattice towers. Consider especially demountable (tilt-over) types that enable fitting and maintenance of such heavy CCTV equipment to be done safely at ground level.
Now we’ve successfully acquired our pictures, let’s progress to the next part: getting the signals from A to B, sometimes going as far as C and D too.
2. Send pictures to their destination: or ‘signal transmission’
Video output from the camera could be:
• composite analogue signal (1 volt peak-to-peak, CCIR, PAL)
• IP video (Internet Protocol) as TCP/IP or UDP multicast
• HD-SDI, High Definition – Serial Digital Interface.
Simple co-axial cables might carry any of these three signal types. Make sure to check all such technicalities with manufacturers of the devices, especially limitations such as distance and number of video signals per cable. The greater bandwidth and low loss characteristics of fibre optic cables make the carrying capacity of any of these signals much greater, albeit more costly, but large ‘bundles’ of signals can make this more economically viable. The other type of copper cable, UTP (unshielded twisted pair), is commonly used for IP the world over. With ‘balun’ interfaces, such ‘Cat-5’ and telephone cables can carry analogue video too. Using public utilities’ cabling infrastructure in the form of broadband Internet services is often viable for IP video, with bandwidth (hence, video quality) governed by price.
Alternatives to cables are wireless transmissions. These include dedicated and licensed microwave line-of-sight links, licence-free microwaves over shorter distances, some of the latter types being WiFi links. Cellular data services such as 3G and GPRS can also carry video, albeit with limited bandwidth and service coverage. 4G roll-out might improve the possibilities.
Now we’ve successfully delivered our pictures, let’s progress to the next part: managing the pictures.
3. Managing the pictures that arrive
Most common is that multiple video signals arrive at a CCTV control and monitoring point. So a switcher is necessary to direct every picture to the right place. Analogue video switchers might be desktop ‘8-in, 1-out’ or a large, expensive ‘128-in, 32-out’ matrix.
Often, images are digitised before or immediately after they arrive. These can be switched in software such as that in a DVR / NVR (digital / network video recorder) sometimes dubbed a ‘virtual matrix’. Bolt-ons to this bundle of incoming signals might be ANPR (automatic number plate recognition) or VCA (video content analysis) machines. Either way, after switching, the outputs commonly go to two destinations: displays and recorders. Analogue signals go to CRTs (cathode ray tubes) or LCD or plasma screens with inputs for analogue video. Video that has been digitised during the first, second or third of this article’s ‘bites’ is fed to displays via the computerised innards of the DVR, NVR, virtual matrix, etc.
Analogue or digital, the pan/tilt/zoom telemetry signals come from the CCTV operator’s control keyboard or, for instance, automatic preset positions triggered by alarm sensors. Recorders are almost universally digital these says, so exporting footage to give to others uses hard copy printers, CD, DVD or portable memory devices.
I hope it’s now apparent how many devices can be used to create a CCTV system in Georgina ‘from soup to nuts’ or literally from light into the camera to light into the operator’s eye. However, when broken down into these three fundamental bite-sized stages, it is much easier to digest.