It’s true to say that the total reliability of any access control system is largely determined by its weakest part. If people can’t open a door with ease on a regular basis, for example, they’ll start to force it and its structure will be damaged. In turn, this may hinder the use of any adjacent card reader. It follows that a successful installation will be one that uses the right kit in the right way.
There are several components that will be vital if you want to ensure that your access systems fall into the ‘fit-and-forget’ category (something that end users always pray for, but rarely manage to attain – through no fault of their own).
Take power supplies, for example. A low power consumption for your access systems will give rise to low heat dissipation, ‘cool’ running and low thermal stresses. In addition, battery lifetimes will be extended. You’ll also need overvoltage transient protection via metal oxide varistors to limit the effects of mains-borne lightning strikes and standby generator switchovers, etc.
In terms of battery back-up, you should always try to ensure normal operation without recourse to an uninterruptible power supply system. Battery condition monitoring is an important task, of course, as it measures battery capacity and not just the voltage. If you do this, it will be worthwhile – there’ll be no sudden and inconvenient ‘lack of power’ discoveries during mains failure.
Watch out for ‘statics’
People walking around the office’s ‘plastic’ carpets with shoes that have soles boasting high dielectric strength can generate up to 30,000 volts of electrical charges. When they touch an access lock, card reader or egress button this energy will be discharged into the earthing system, but will also couple into signal cables and low voltage power supplies. Very fast (radio frequency) transient bursts will then be produced, with the potential to upset the microcontroller and make it crash.
With this in mind, sophisticated system monitoring hardware must be used to ensure early crash detection. The microcontroller can then be re-set in order to restore control to the system firmware. Needless to say it’s highly likely that the cardholder database will also have been corrupted – either by the electrical pulsing itself, or as a result of the processor ‘running wild’.
Lightning strikes are becoming much more commonplace than in years gone by. In truth, they’re capable of producing very large amounts of electrostatic energy which will try to go for earth by way of any exposed network or power cables. There’s a limit to the amount of protection the equipment manufacturer can provide internally for some of these sources because of the need for good low impedance earthing with minimal coupling to the rest of the circuitry. External suppressors are also available, and need a good direct earth connection.
Fibre optic networks have proven to be an excellent method for building networks with true high voltage galvanic isolation between buildings. Unfortunately, the use of such networks is still pretty minimal in the UK. One solution which end users might consider, and which has also proven to be successful (both in testing and in practice) is specification of the Integra product range.
The Integra system explained
The Integra system uses a separate processor card (with most of the noisy/sensitive digital electronics on it). A separate Input/Output (I/O) card is then loosely coupled to the processor card, thereby allowing a considerable deviation in I/O potential to take place without inducing large currents in the processor card. All input grounds (cable screens, etc) are returned direct to the system chassis ground from the I/O board, ensuring that as much of the external energy as possible does indeed go straight to ground.
Interestingly, CE marking and electromagnetic compatibility testing are continuing to play a major part in encouraging access control system manufacturers to devise products which are inherently stronger in the above respects.
In the event that an access control system crash does occur for whatever reason, the end user’s ability to make sure the system is up-and-running automatically – assuming that the affected unit(s) has/haven’t been damaged irreparably – will centre on the concept of distributed intelligence. This doesn’t require any intervention from a host computer which may have either been damaged, or has failed for another reason.
What is distributed intelligence?
Distributed intelligence is the exact opposite to centrally-processed intelligence. Computer terminal equipment which is fully functional even when the central unit to which it’s attached is not available is a good example of a distributed intelligence system.
A failure of centralised computing may be found at an airport check-in, or when on the telephone to the bank, and we’re subsequently told that there’s a problem with the computer or the communication lines such that the airline staff are unable to check you in or give you the information that’s needed. In this case, distributed intelligence would be attained by giving each of the parties involved a computer containing the full database – enabling the system to continue to work regardless of what the others were doing.
If this concept is applied to the security industry, and in particular to access control, then a fully-distributed intelligence system is one where not only is the access control decision made at the point of entry, but it’s also where the entire system database is stored.
In other words, at no time does the system need any help from a higher level unit or computer in order to make the correct access decisions speedily from its local database.
As far as the IET networking access systems are concerned, the availability of this multiple copy database is taken a stage further. In the event that an access control unit loses part of its data due to power failure, maintenance or electrical disturbance, because every unit on the system is a master – there are no slaves – any unit will automatically restore the current database from other units on the system. This capability further enhances system reliability.
What most certainly isn’t distributed intelligence is when the full database isn’t actually available at each access control unit.
Likely security scenarios
Based on the above, let’s suppose that you have a site to protect. You want the best for your building(s), and you propose a system with fully distributed intelligence. The site has seven perimeter doors or barriers. The system that you’ve selected makes use of controllers that each have the capacity to control eight card readers, and is ideally suited to the site layout. As a result, one of these controllers is designated to protect all the card readers at the perimeter access points.
Effectively, this means that a lone access control unit now controls all of the perimeter access points, and that you have in fact created a centrally processed system for the site perimeter. You have also provided the company with a system wherein full distributed intelligence has been removed.
What you wanted was a system so designed that should any processing component fail, as few access points as possible would be affected. With this proposed system, if the access control unit handling the perimeter access points fails then you have jeopardised the entire perimeter of the site.
This example begs the question as to how many card readers a controller may handle and still be considered as a fully distributed intelligence system. The ideal situation would be, of course, to have a controller containing the full database at each individual access point. Of course, in reality this isn’t very practical, and would prove to be extremely expensive.
Access control units with the ability to control a maximum of four doors are a good compromise, although great care should be taken when proposing a system where maximum security is an overriding requirement.
A final pointer for end users… Be careful! Note that some manufacturers’ systems purporting to have distributed intelligence do so because the processing isn’t carried out by a host PC or the local access control unit, but by another remote unit. These low budget systems invariably fail to provide sufficient security and reliability.
