This article looks at the needs of the more complex industrial and commercial systems. There are, of course, plenty of do-it-yourself CCTV systems on the market that provide excellent quality and performance.

During a visit to a site demanding a very high level of security, the views on two CCTV monitors were noticed as being appalling, with almost no definition. This was not commented on at the time because the visit was for a totally different reason. Later, however, a comment was made and the customer stated that the installation was technically very difficult and the installing company had said that this was the best that could be achieved under the arduous conditions that prevailed at this site. Engineers had returned on many occasions and could not improve the picture quality. The expectation of this customer was, therefore, that with all the technical resources of this large installation company, he was obtaining the optimum performance. An inspection of the site was made and the conditions were indeed demanding. It was discovered that the cameras were up to one mile away from the control, and underground, the illumination being by means of infra red lights. The cameras were connected back to the control by a very large coaxial cable. Furthermore, at the control the video signal was fed to a video motion detection system, and then on to five separate monitors.

A series of tests was suggested to which the customer agreed. It was intended to replace the coaxial cable with a 'twisted pair' but site conditions precluded this possibility. A video launch amplifier, designed to send a video signal down a coaxial cable, was fitted at the camera end and a line corrector at the control end. This resulted in a dramatic improvement in picture quality and, for the first time, the video motion detection system worked correctly. An additional light was installed at the camera end to increase the levels and allow the lens to operate at a smaller aperture, which increased the depth of field. There were still problems with the remote monitors until it was discovered that they were all terminated at 75 ohms. Simply setting all except the last monitor to 'high z' cured this problem.

This was a classic example of a poorly designed and badly installed system. The tragedy was that the customer thought that it was the best that current technology could produce. He may well have been put off CCTV as a practible proposition for future applications.

The system comprised four cameras around the outside of an industrial building, connected to a quad screen splitter and a time lapse video recorder. One of the cameras was also connected to a video motion detector covering the main entrance.

The customer's expectation of the system was that, if a vehicle entered the yard outside normal working hours, the system would go into alarm. The identity of the vehicle and any other activity around the building would be recorded. Here was the first flaw in communication; the customer's interpretation of 'identity of the vehicle' meant reading the number plate, but he also wanted to see the entrance and where the vehicle went.

The quad screen splitter was set to record a full picture on alarm, so the other cameras were not being recorded. Even if the splitter was not set in this mode and recorded in quad screen, the pictures would be too small to be of use.

The time lapse video recorder was set in 24 hour mode and switched to real time on alarm. The problem was that, with only a few incidents over- night, reviewing the tape was a tedious procedure (assuming the system had worked as intended).

In principle, the system seemed reasonable on paper and the customer would have no basis for doubting what was presented to him. However, the individual items were not correctly selected. The person who designed the system had obviously come across various pieces of equipment through exhibitions and advertising, but had no depth of understanding of the specifications or what questions to ask of the manufacturer. Also, it was apparent that the system had been designed down to a price under pressure from the customer. It is a sad indictment of parts of the industry that sales people try to find the cheapest solution rather than concentrate on finding the right solution. Even sadder is the probability that many do not have the training to know the right solution. The following changes were made to produce an acceptable working system.

The video motion detector initially installed was a type only designed for indoor use, or limited outdoor use in fairly constant lighting.  A phone call to the manufacturer confirmed this. The unit was replaced with a budget version of a more sophisticated video motion detector with a range of more sensitive set-up parameters. This functioned as expected.

The lens on the front camera was changed to one with a longer focal length so that it only viewed the area that would catch vehicle number plates. Also, it was moved higher up the wall and looked down at the area to avoid the problem of looking directly at the rising sun.

The camera viewing along the front of the building was swung around to view the general area of the entrance.

The time lapse video recorder was replaced with an event recorder that only recorded in real time when an alarm was active. This provided rapid reviewing of the previous night's, or even previous week's, events without the need to plough through hours of inactivity.

The result was a system that achieved the expectation of the customer, although at considerable unnecessary cost to the installer. The cost of the final equipment installed was not a great increase on the original and would certainly not have lost the company the contract.

Whilst there are companies that offer a competent and professional service, there are many more that do not have the depth of technical knowledge to design larger systems that produce acceptable results. In the case of CCTV in particular, there are many factors that must be taken into account in designing an effective system. In some instances there may be restrictions caused by the Laws of Physics of which the customer should be appraised. Some of these factors are listed below.

· There is a limited depth of field in focus in low light conditions when the lens iris is fully open; it is also a function of the focal length and the object distance. The depth of field decreases when the 'f' number is smaller (the aperture is larger); the focal length is longer; the object distance is shorter.