Hi, and welcome to the eighth paper on access control. This session we start unit four in the series. This unit covers single door controllers and associated software, operation and architecture of multi door systems, central data gathering and display units and software features of multi door systems.
Singlr door controllers
A single door controller (as you may have guessed!) is an item of equipment that controls a single door and, as such, is the smallest possible system in access control. It can thus be seen as the smallest access element in a large system.
Single door controllers offer great complexity and can provide the facility to programme tokens uniquely for each individual. This allows data such as personal identification numbers and access times to be associated with each token. There are also many more features that can be added. So, what do we need to create a single door access control system?
Minimum equipment
1. A method of identification such as a keypad and/or token and token reader.
2. A controllable door lock.
3. A processing unit capable of distinguishing between authorised and unauthorised personnel.
4. An appropriate power supply.
5. Communications, control and power cables between the items.
Those listed above are a minimum. Additionally, you may have the following:
6. Door open sensor.
7. Door open timer.
8. Door lock sensor.
9. Door lock timer.
10. Door closer.
11. Exit button.
12. Alarm inputs.
13. Relay outputs.
At the heart of any controller is usually a small computing system that makes all the decisions about the token offered i.e whether it is valid. Let's look at the make-up of a typical controller.
Processing unit
The processing unit or controller is the heart of any access control system and it determines the access rights of personnel wishing to enter the access point. To enable it to perform this function it must have several essential components: Microprocessor, Memory, Input & Output capabilities. Let's consider each of these in turn.
Microprocessor
The microprocessor is the decision-making component of the controller. Using the information stored in its memory, it determines whether or not a token, code or physical characteristic is valid for use at that access point.
Memory
The memory is important because it stores three vital sets of information:
1. Programme data which tells the controller how to behave as an access control system ... its "rule book".
2. The configuration data which provides the system with the necessary information about the site on which it is installed.
3. The history data which tells the user of past events that have been logged by the controller.
Together the programme rules and configuration data control the operation of the system, with the configuration data supplying the information for the programme to make decisions. The programme information will usually be installed into the controller's memory at the manufacturing stage, so does not usually require any action on our part to ensure it works.
Data input & output devices
As you may have seen from systems that you have worked on, the most common form of device for data input is the keypad. The numeric keypad is usually cheaper and can be easily installed as part of the controller's electronics, making them permanently available for use. However, a numeric keypad does not allow the use of alphabetical characters like a person's name and is difficult to use when inputting large amounts of data. Due to their higher price and larger size, keyboards are rarely provided as part of the standard electronics of a single door controller.
Output devices are typically available in three formats: visual display units (VDU), liquid crystal display (LCD) units and light emitting diodes (LED). A fourth format is a printer, which we shall discuss later.
LEDS were among the first output devices to be used but LCD displays are now more common. This is because of their low power and small size, enabling a variety of messages to be conveyed on a small screen and, therefore, a reduction in cost. Since a readable message can be displayed on a small screen, an LCD unit can easily be mounted into most controller housings and is now the most common output format used in single door controllers.
A VDU will rarely be found on a single door system because of its (comparatively) large size and high cost.
While the output devices we have talked about are useful for displaying changing messages, they are not suitable for the display of permanent messages such as times that certain staff entered the building, lists of alarms etc. The device that is suitable for this task is the printer.
Printers are available in a variety of shapes and sizes and can be designed to fit into the controller's housing. The price of such printers tends to make their incorporation into single door controllers an expensive proposition, so a more common option is to provide a printer port into which a standard size lower price printer can be connected.
Correct cabling between components is critical to the success of any access control system and is often the downfall of otherwise well designed systems. Correct cabling between components is critical as access control systems depend on real time communications to pass data speedily to the control system for it to decide whether to release a locking mechanism at the access point.
The data between controllers is sent in the form of small electric pulses which can easily be swamped by sources of electrical interference, attenuated by cable resistance or corrupted by capacitive or inductive effects.
Unfortunately there is no standard choice of cable to use, with each manufacturer specifying their own particular requirements which must be adhered to. However, the following serves as a general guideline: Power cables must have sufficient cross sectional area to supply the correct voltage to the device at the end of the cable.
Data cables will normally be constructed of twisted pairs of stranded or solid core conductors, all of which are surrounded by a standard screen. The use of twisted screened cables is almost mandatory in the access control market as this design of cable is the most resistant to electro magnetic interference (EMI) which can easily corrupt data transmitted in non-EMI resistant cables.
A typical number of cores required for connection to devices with their description. Remember these are only guidelines and may vary by manufacturer. Always consult the manufacturers' specifications.
Additional equipment
1. Door open sensor. This is simply a door contact which changes state whenever a door is opened or closed. A cheap, reliable and simple way of monitoring a door can be achieved by fitting a magnetic reed contact to the door and door frame.
2. Door open timer. The timer is pre-set for a number of seconds which means that once the door is opened by a valid token, the user has a predetermined time to close the door after them, otherwise an alarm will be raised.
3. Door locked sensor. Unlike door open sensors, door locked sensors will normally be integral with the locking device, typically in the keep, and so the requirement should be specified when purchasing the lock and will normally be referred to as a "monitored keep" or "strike".
4. Door lock timer. The door lock timer controls the length of time the door lock is to remain activated after a valid exit has been made. The door lock time will start counting as soon as the lock is activated, with the lock being de-activated as soon as the time expires or after the door closes.
5. Door closer. While this is not a component directly connected to the controller, a suitable door closer should always be fitted to the entry point to ensure that the door closes automatically.
6. Exit button. So far we have considered the types of equipment required to control the entry of persons into the premises, yet equally important is the provision for controlled exiting.
Since most single door controllers provide one reader input only, the usual way of achieving staff exits is through the use of an exit or egress push button. Pushing such a button forces the controller to treat the event as if a valid entry has been made i.e. unlocking the door for the duration of the lock timer and ignoring the door open alarm until the door open timer expires.
7. Alarm inputs. A feature of many modern access control systems is the provision of inputs which are not dedicated to serve any specific access control function.
This makes them available for use on any customer application such as a visitor call button, tamper switch or for interfacing to intruder, fire alarms or CCTV systems.
8. Relay outputs. Finally, the single door controller may also provide outputs, which are not dedicated to serve any specific access control function and thus can be used to activate bells, lamps or be used to send switching signals to other equipment such as the intruder alarm or CCTV system.
We have now covered most of the equipment to construct a functional single door controller. Next month we will be looking at single door controller software.
Source
Security Installer
