A simple way of defining access control is to pose the question: who goes where, and when. This is according to Nigel Versfeld, TeqTrader's Manager of Access Control. In this article, he discusses users' requirements, and provides a few guidelines on the potential pitfalls in installation and networking of equipment.
System specification
It is important to establish the user's requirement, which may, or may not be known. The user often does not quite know what is wanted or needed.
Fundamental questions that need to be asked are:
* Is the requirement for an on-line or off-line system?
* Does the user require anti-passback?
* If so, then he will require two card readers per controlled door.
* How many cardholders are there going to be on the system?
Networking of equipment
Most controllers will connect to a standard RS485 network allowing a network segment length of approx 1200 m. Other options include TCP/IP, wireless radio modem and fibre-optics factors to take into account when considering networking include:
* If one is going to install RS485, use only stranded cable which is twisted by pair and then overall screened. Without screening and twisting you stand the chance of having noise inducted into your data cabling and cross-talk occurring between conductors.
* TCP/IP: This data network is usually cabled using coaxial cable (10/100Base-2) or Cat 5 twisted pair cabling (10/100Base-T). The decision to use either of these cabling systems is usually made by the customers IT department.
* Wireless data modem offers convenience and ease of connection across difficult areas and terrain. Considerations are complying with SATRA regulations with regard to transmitting signals across public roadways, frequency and frequency licence application through SATRA, line-of-sight communications.
By simply installing fibre-to-copper, and copper-to-fibre converters one can easily transmit data signals over vast distances using fibre-optic cable.
Installation
The area of an installation that has the greatest potential to destroy a company, product and reputation is the installation of the network and the termination thereof.
All too often poor grade cable is used which causes data communication errors, or cables are not terminated correctly with ferrules, glands, etc. Other concerning factors are when:
* Cables are run alongside HT mains power cables, and even in the same ducting.
* No clean power supply source is used and 'dirty' power is often taken off factory floor equipment. Induction motors are a very bad noise source.
* Every cable joint adds resistance to the cable and thus attenuates the data signal strength.
* All cabling should be 'home runs' without any joints.
* Correct earthing and surge arresting are often not employed by the contractor.
System failure can be expensive and exhausting to find the fault, especially if it is intermittent. If the time is taken to ensure good and proper installation work, then the system will usually run for years without failure.
Maintenance
After the warranty period has expired it is worthwhile entering into a maintenance agreement with the customer to ensure continued and reliable operation of their system. Do not let the customer think that the system will not require maintenance.
Most computer networks require constant calibration and checking to ensure reliable operation and maintenance should cover hardware and software. In addition, power supplies, UPSs etc should be checked for reliable operation in case of a power failure. Service packs and firmware upgrades should also be actioned during the maintenance intervals.
For further details contact Nigel Versfeld, TeqTrader on tel: (011) 403 3002, fax: (011) 403 7997.
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