HAVING DECIDED WHAT IS REQUIRED for each camera position, we must now consider how the information will be fed back to the control point.
In the majority of situations, cable will be the best method, but the route and its length have to be considered. And if the cable is to run across free space, between buildings etc, ducting or catenery may be required.
Underground ducting can be very expensive to lay, but in some situations this may already exist and can be used, although public service ducting, such as gas, electricity and telephone, cannot. The entry and exit points need to be established at the time of the survey, and if cables are to be run into existing ducting a draw wire will be required so that the cable can be pulled through.
If the cable is to travel over ground this can be done using a support wire known as a catenery. There is a limit to the distance over which this should be used, depending on the number of cables and their weight, and there must be solid fixing points at each end of the wire. Public utility poles cannot be used to support these runs.
Cable length
Cable lengths must be checked against the types of cable specified. For very long runs it may be necessary to add a video amplifier to compensate for losses. Above this length it may be necessary to use an in-line amplifier to boost the signal.
Cable routing should also take account of heavy machinery, radio transmission points and any area that may cause unwanted signals to be induced on to the signal path. Electromagnetic interference (EMI) can cause severe problems, and proximity with any possible source should be avoided.
Cable type must also comply with building and fire regulations. This is particularly likely to affect installations in public places such as cinemas, theatres and clubs. The cable rating, smoke emission and fire-resistant qualities may be subject to local standards and this should be checked.
Where cable is impractical, one of the other signal transmission methods may have to be used, as discussed in previous papers.
Establishing the control point
Having decided the number of cameras required, we can consider how they will be controlled and reviewed. This is likely to be dictated by the custo-mer’s requirements and their operational system – figure 1 shows a profile of what may be required:
Video switching
If video switching is required, the size of the unit will be dictated by the number of cameras and the number of outputs needed. It is also wise to allow for expansion – this reduces the cost of adding on cameras later and gives the system more flexibility.
Monitors
The number of monitors will be governed by the customer’s requirements and the size of the system. If there is a large number of cameras it is often better to split them up between several monitors rather than displaying them all on one unit. The use of a number of monitors is likely to be limited by the space available, the system budget and viewing capabilities. The size and location of the monitor must be carefully selected, and in choosing the size of screen you must consider the amount of information that will be displayed as well as the viewing distance.
Video recording
The choice is between domestic, event and timelapse recorders. If a record time of eight hours or less is acceptable, it is better to use a domestic machine as they are cheaper. If extended recording is required, a timelapse recorder may be necessary. Establish the maximum record time required so that the most suitable recorder can be used (there is no point in specifying a 480-hour recorder if the maximum ever needed is 24 hours). Also consider any effect the slower sampling rate might have on data collected. In a till audit situation, for example, the speed of data can result in some omissions if the time between sampling is too great.
If the recorder is to be used with multiplexing, the two units must be compatible to ensure the most effective sampling time is utilised – some timelapse recorders operate on a field record basis while others work on a frame-based recording. The recorder sampling rate has to be matched to the multiplexer output rate. This is normally programmed into the multiplexer by the manufacturers but it is important to ensure they do support the particular recorder chosen.
If recording is required only during limited periods, such as during a break-in, then an event recorder could be used. This would be activated by an external trigger such as an alarm.
Camera control equipment
If there is a motorised camera unit or lens, some form of control system will be required, either hard wired, relay wired or telemetry. For small installations hard wire systems will probably be the most cost-effective method, while for larger systems telemetry may be better. Where there is more than one camera you could combine the telemetry control unit with the camera switcher.
Peripheral equipment
You may now have to consider whether any peripheral equipment will be required in order that the system will meet the customer’s requirements. This may include adding a time-and-date generator (if not already present in a timelapse recorder). If hard copies of a picture are required you may need to add a printer.
Compatibility
The important point to remember with all this equipment is compatibility – it must all be capable of working together. This extends beyond ensuring that all equipment is capable of handling the 1 volt pp video signal.
Putting it together
Having established what is required and where it will go, we need to bring it together as a system. We also need to communicate this information clearly so that it can be assessed for pricing (if you are not already doing this), and because it is likely to be the basis for the installation brief.
Communicating everything that has been agreed with the customer is important, not only to protect them but to protect the company as well. But communicating accurate information is not always as easy as it sounds, as everyone tends to interpret things differently. The methods used will vary as different companies use different systems, though in general it will be through a mix of written details and drawings or pictures.
Because CCTV deals with pictures and concepts, it is very easy for misunderstandings to occur. Here are a few points that may help to prevent them:
The site plan
If one is not already available from the customer, you may have to draw one. It does not have to be elaborate or even to scale as long as distances are given – the most important thing is to give an indication of the site’s layout and size.
The position of the equipment should be marked clearly and cameras numbered to indicate where each camera is located.
System schematic
This should reflect the wiring of the system and be laid out in a clear and organised fashion. A good schematic could be likened to the London Underground map – it may not show the exact physical layout but it provides a clear understanding of where everything goes. Figure 2 shows how it should and should not be done – a well laid out and easy-to-follow schematic next to a clumsy and difficult-to-follow one.
