Choosing a CCTV Camera

There are many styles of CCTV camera available but depending on the operational requirement, the best-suited camera should be selected. Fixed cameras in housings offer the ability to have larger lenses and wipers to clear away rain, whereas cameras in domes look more tidy and are generally cheaper. The same applies to pan, tilt and zoom (PTZ) cameras where an overt version has the ability to have larger lenses and have bolt on equipment such as a wiper and illumination that rotates with the camera. The dome versions have the same advantages as the static domes, i.e. tidy and generally cheaper but are limited if they have a tough operational requirement.

Cameras can produce colour images but colour viewing is limited by the amount of light that it needs to operate. There are digital signal processing techniques that allow a colour camera to see in relatively low light conditions but this processing has a price attached, which is often quality of image. Monochrome cameras see at much lower light levels and are sensitive to infrared illumination, which makes them ideal for night operation. To overcome the need for a colour camera during the day and a separate monochrome camera for nighttime, colour/mono or day/night cameras automatically switch from one mode to the other dependant on the available light.

Cameras can be categorized by their image sensors; the Charge Coupled Device or CCD chip is a light sensitive plate that converts the light focused by the lens into an electrical signal for processing. CCDs come in a range of technologies but the more basic criteria for categorizing a camera by its CCD chip is the diagonal size of the receptive area. The larger the CCD chip, the more light it can gather. In closed circuit television system CCD chip sizes are generally1/4”, 1/3” or 1/2”. The larger chips generally mean that the camera is more expensive.

The resolution of any CCTV camera is the key to the performance of the system. Resolution is the measurement of the picture quality in terms of how much electronic information is gathered. An analogue CCTV camera measures its resolution in Television Lines (TVL). These horizontal scans make up the video signal. The more horizontal scans there are in the image, the more detail the system captures and the clearer the resultant picture. The resolution is directly related to the number of pixels within the CCD chip. A low resolution camera would typically be around 330 Television Lines (TVL) and a high resolution camera would be from 480 to 540 TVL.

CCTV cameras also vary in the amount of processing that they do to the image before transmitting it to the control equipment. A high quality camera would have a range of processing features such as backlight compensation, which reduces the effect of silhouetting and automatic gain control to boost the video signal when light levels drop. For more demanding fields of view there are features that allow manual override of the shutter speed and wide dynamic processing. Wide dynamic processing allows the camera to produce high quality images in challenging conditions such as high contrast lighting produced by flood lights.

For true night vision there are thermal imaging cameras which detect very low heat sources and displays the image in a useable format.

When it comes to choosing the best CCTV camera the important considerations are around what you need to achieve based on the operational requirement.

Where do you start when designing a CCTV system?

To get value for money and an effective CCTV system you must have an understanding of what you need and how to achieve the desired results. The design process for a CCTV system can be quite complicated. I have been called in to many systems and asked why has it had little to no impact on the original problem. The answer is usually because the original problem was not clearly identified and the performance requirements of the CCTV system were not considered. The end result is a pile of CCTV equipment installed that does not do what is supposed to.

Before considering the implementation of any CCTV system, it is important to understand what the problem is and whether CCTV is the most appropriate solution. The production of an operational requirement document will ensure that the key points are considered, such as why do I want CCTV, what is its purpose, what will it achieve and what will the performance criteria be.

Firstly make a statement of need that defines the problem and assesses the potential impact of CCTV upon it. I.e. will the introduction of CCTV alleviate the problem?  This statement shall clearly define the problem and the solution.

The second part of the operational requirement will detail specific problem locations and the required performance specification, both technically and operationally. For example, a camera on the perimeter of a site may need to be able to “Detect” a person engaged in a particular activity under low light conditions. The performance of a CCTV camera, in terms of operational requirement, can be defined within five surveillance categories.

Monitor and Control – A person occupies at least 5% of the overall CCTV image height.

Detect – A person occupies at least 10% of the overall CCTV image height.

Observe – A person occupies at least 25% of the overall CCTV image height.

Recognise – A person occupies at least 50% of the overall CCTV image height.

Identify – A person occupies at least 100% of the overall CCTV image height.

This part also details the operational issues of who monitors the system, where and when. A recording archive quality and duration must be established and high-level Standard Operational Procedures produced to determine the appropriate response to any given scenario. It is also important to establish a method of transmitting the procedures to the response team to ensure that the correct response is initiated, bearing in mind that some scenarios will be rare and procedures may not be instantly familiar to the team.

With the operational requirement document in place, it is necessary to consider the technical specification to fulfill the requirement. A detailed specification should be produced that can be used for the purchasing process and a system for commissioning and validation of the system should be documented.

What is transient suppression and do I need it?

Modern societies rely heavily on electronics for every aspect of life. From health and economy to entertainment and security. The basic fact about electronics is that it uses wires or cables to transmit power and signals. Let’s put wireless to one side for now because there is not yet a viable wireless power transmission technology, which means that even wireless systems rely on connection cables at some level.

This fundamental reliance on metal conductors means that one rule of physics is unavoidable. This is that electromagnetic fields can induce electricity into an adjacent metal conductor without physical connection. Therefore, an intense burst of power near a cable can induce a damaging spike of electricity into that cable without being in contact with it. This spike is likely to damage or disable the electrical systems that the cable serves.

So what causes these spikes? Lightning is the big one given its strength and the amount of cables that are lying across the planet but lightning is not the only source of damaging spikes. Spikes are more likely to be caused by heavy machinery switching on; motors and appliances such as air conditioning can also cause damaging transient spikes.

Another name used in connection with these spikes is overvoltage. The term transient overvoltage literally means a momentary electrical spike. These spikes can overheat components in the electrical system or breakdown the insulation that contains the signals. Either way, system damage can be catastrophic.

You may have designed the best security system ever but without adequate defence, it is at risk of problems or complete failure if you don’t consider transient protection. The difficulty for the system designer is to keep the amount of protection proportional with the risk of induced overvoltage. You may consider that a domestic property in a low lightning area would need far less protection than an industrial process plant in a high risk lightning area. This assumption is probably correct but the risk assessment for how much protection is required needs to consider the potential should a system fail as well as the hazards that may cause the voltage spike.

Considering the domestic property again. The property does not have heavy machinery turning on and off but it does have air conditioning, which is quite old. It also has domestic appliances such as refrigerators etc. The wiring in the property is also old and is bunched up as it runs around the house. It’s a large house that belongs to a very wealthy person that doesn’t trust the banking system so keeps a quantity of bullion on the premises in a safe. Although the property is in a low lightning risk area, it is not unheard of that lightning strikes the ground occasionally. This person is often away on business and leaves the house empty for days at a time, relying upon the security system to alert him and the authorities if anything unusual occurs. The risk of transient overvoltage affecting this security system is quite low but the potential for loss is quite high. So the question is now, does this domestic property in a low risk area need transient suppression to protect the security system?