Several devices can be used (see Fig 1):
- Door contacts
- Pressure pads
- Passive infra-red units
- Ultrasonic detectors
- Microwave detectors
- Active infra-red detectors
There are other devices, such as field effect detectors, loop alarms and tremble switches, but these are not normally used in connection with CCTV systems.
Alarm interface board
By linking these devices to an alarm interface board, a sophisticated system to activate a video recorder and video switcher can be developed. The alarm board provides a set of open and closed contacts that can be used to link the alarm input of the recorder.
An individual camera can be selected through an alarm input switcher by having a detector linked to each camera viewing zone. Each zone activates a different set of contacts, which are linked to the video switcher. A closed contact across the switcher causes the unit to select the required camera (see Fig 2).
System design and specification
System design and specification is a specialist task that may be carried out by a trained sales person, consultant or the customer's own security staff. Part of the assessment process is to identify the overall problems and needs that the system is expected to address.
CCTV can then be used to meet a part or all of that need by fulfilling one of four functions:
- Providing visual evidence of an intrusion or event
- Providing additional security through visual control or detection
- Risk reduction through identification and storage of information
- Providing management information.
The task of the CCTV surveyor is to design the most suitable system to meet these needs, which sounds straightforward enough but there are likely to be constraints – in particular financial constraints – that restrict the way in which this is achieved. Finding the right balance is part of the art of system design.
Reaching an agreement
It is likely that the request for a system specification follows an enquiry or sales visit and the survey will form the basis of a quotation.
If successful, the quotation will become part of an agreement between your company and the customer. This agreement will end with your company making a profit or loss on the installation, and the customer being satisfied or otherwise with the system installed. The actual outcome is heavily dependent upon how accurate the survey and specification have been.
The activities that might be undertaken during the design stage are:
- Determining the number of cameras, their location and view
- Designing the best control and review system for the customer
- Deciding the most appropriate form of signal transmission and its routing
- Determining what peripheral and ancillary equipment, if any, is needed.
The activities that might be undertaken during the specification stage are:
- Determining which type of cameras will be best suited
- Calculating the lens requirements for each camera
- Deciding which type of control equipment is best suited
- Specifying cable types and signal transmission equipment, if required. Determining mains supply requirements
- Specifying suitable peripheral and ancillary equipment
- Preparing equipment list and pricing schedule.
Although we have separated the two functions to allow explanation, in practice the two go hand-in-hand and are often carried out at the same time.
Keep it simple
The first thing to remember in designing a system is the KIS approach: Keep It Simple. Any system should be designed to meet the customer's requirements in as simple a way as possible.
The second thing to remember is that design and specification are the first steps in the process, the foundation stones of the system. The system's fitness for the purpose depends on the quality of the work carried out by the specifier.
Before we can design a system that will fulfil the customer's wishes, we must find out what they expect and understand any constraints.
Questions to ask
1. What problems does the customer want the system to address?
There will be specific problems or needs and we need to identify the most important and, if possible, agree a list of priorities. In this way the system can be designed to address problems in order of importance within the financial and practical constraints.
Never assume you know better than the customer, no matter how much experience you have. Try to work as a team, with the customer providing the information and you the expertise.
2.What does the customer expect from the system?
Finding this out can often be enlightening. People's expectations are often fuelled by a lack of understanding, particularly with camera views and the amount of detail expected.
It is vital that the customer's expectations match the system's ability. If it doesn't you will not have a successful system.
3. How will the customer use it?
There is no point in providing a customer with a system that will not be used fully – it must be designed to fit in with their working practices. If the customer is prepared to change these, there must be a full understanding of what is involved to accommodate the system.
In deciding how the system will be operated, consideration must be given to the human element. CCTV provides little entertainment value and watching one or more screens will rapidly induce boredom. This leads to loss of concentration and mistakes. Viewing times should be short, so it may be necessary to rotate staff.
If the system is unmanned, will recordings be reviewed? If so, the same problem applies – review times must be kept to a minimum.
4. What are the cost restrictions
Customers may not always have a fixed budget and, if they do, they may not be prepared to tell you. Trying to design a system without some guidelines is very difficult, but a good start is cost justification.
The system must offer some return on investment in some way – this may be through reduced wastage or losses, reduced insurance premiums or labour costs. Other, less tangible, benefits such as reduced risk to health and safety are just as valid.
If you do not have a target, it is better to be flexible and offer several options. Work with the customer to establish where an acceptable level lies. It is likely that they will seek more than one quotation, so offering several options can help when competing for business.
5. What other constraints are there?
Other constraints that may have to be taken into consideration could include how the equipment looks, where it is placed and how it will be used.
Source
Security Installer
