Access point operating modes.
Recently, I've been hearing more and more often that access control systems are competing in some system parameters — one can work with 10,000 cards, and another — with a million. One can service 250 checkpoints with turnstiles, and another — 5,000 checkpoints. One works via radio, and another via the Internet.
I want to draw attention to the simplest functions of each access point. Not all systems (in fact, none of those that I know) implement all the capabilities listed below. But all these «know-how» have ceased to be novelties for 20 years. Why, in most cases, are they not implemented in all new systems in a row? Just laziness?
All systems support work with an access point consisting of a lock, a door, and one reader. In such a simple configuration, do you think everything is simple? Not at all.
Let's start with the reader. Readers are more or less standardized these days. The so-called Wiegand interface. In fact, they differ, for example, in the number of bits sent. However, most controllers can only work with the most common 26-bit version. So if you want to maintain compatibility with previously installed old systems, not all new controllers are suitable. And some controllers even allow you to use different readers in one system, independently converting their data to a single form.
By the way, some readers can regularly send a short data packet so that the controller knows that the reader is intact and working. However, I know very few controllers that can receive such a signal.
Also, in our country, readers with an interface that imitates I-Button (colloquially — Touch Memory) are quite common. They are not at all similar to the Wiegand interface and often differ in the name by some inconspicuous suffix, so you will discover the supply department's mistake only after installing the system. And what will you do if the selected controllers only support Wiegand?
What's even worse is that readers come with one or two LED indicator control wires. Of course, the one-wire option is less common, but controllers that can control it are even less common. What's worse, some controllers assume that the reader has two LEDs and one buzzer. And if you buy cheap readers (for example, without a buzzer or with a single-color LED), the beautiful system indication will become unclear. And all this reduces the choice for special cases when you need to install, for example, a long-range reader on a car gate.
However, compatibility issues are really rare. Let's discuss what useful functions controllers can actually have during operation.
The system can distinguish whether a person passed through when he was allowed or not (of course, it will not actually know whether he passed through or not, but at least whether he “opened” the door or “did not”). Why is this necessary? First of all, to ensure control over repeated passage. So that the system knows that the person passed into the next room and, therefore, can now quite legally try to go further. And in general, if the system has an event log of a million entries, it is strange if it does not record the difference between “access granted” and “access completed”. Most systems can detect “breaking in” (i.e. opening the door without the system’s authorization) and “holding”, when the door remains open for more than a specified time. But not all systems allow you to configure the duration of permissible opening (and doors are different: in the main building of Moscow State University, I remember, you had to open the doors with both hands, and they did not close quickly). In addition, in some conditions, both breaking in and holding may be permissible. For example, during the reception of visitors, the lock is mechanically blocked, and the door can be opened without an impulse from the ACS. If the system registers a «break-in» every time, then it will be difficult to find a real break-in against this background. Similarly, when furniture is brought into a room, the door, of course, is propped up with something, and it stands open. This is not scary, a security guard or a responsible person is standing nearby. But if the system beeps annoyingly or, even worse, turns on a siren for the entire building, you want to find its author and express all your obscene thoughts.
By the way, if the system can quietly beep when you forget to close the door, that's good. Often the door just doesn't close completely (some trash got into the crack), anyone passing by will notice that the system is beeping and will fix the situation. Otherwise, the door would remain unlocked until the end of the New Year holidays. However, if this function cannot be turned off (preferably right there, on the door, without going far, for example, by presenting a card to the reader while the door is open), then people will be unhappy and will do something so that it doesn't get on their nerves. For example, they will turn it off altogether.
By the way, good systems have several door control inputs. One for the door sensor, and the second for the lock sensor. Good locks may have an additional built-in contact that signals that the lock has actually locked the door (in electromechanical latches, this is a small limit switch in the bolt socket, in magnetic locks, this is a Hall sensor that controls that the plate has closed the magnetic flux).
In addition, the system can have settings for working with different locks. Of course, almost all systems have an «opening time» setting. This is important, because, say, for a magnetic lock, it must be de-energized for a time sufficient for a person to understand that the door is unlocked and open it. This is 5-10 seconds. For heavy motor locks, 20-30 seconds may be needed. And for latches with a mechanical cocking, 3 seconds is often the maximum time after which the lock will melt (read the instructions for the lock carefully). But it is not enough to set the lock opening time. For the aforementioned locks that can burn out, it is necessary that even if someone presses the exit button and holds it, the impulse stops and starts again no earlier than a few seconds later (let the solenoid cool down). And many systems directly transmit a signal from the exit button to the lock. Someone leans their shoulder against the button — and that's it, the lock has burned out again, it needs to be replaced again.
But that's not all. The mentioned motor locks are easy to control if the opening impulse to the lock is forcibly extended for the entire time until the door closes. Then the lock will go back to lock only after the door closes. Of course, you can install an external unit that provides such control, but, honestly, it's funny: there is a powerful system praised by the seller and additional boxes are connected to it, because it «doesn't control the lock correctly».
By the way, the above applies not only to the rare motor locks, but also to barriers, which are much more common. To prevent the barrier from hitting a leisurely car on the roof, in most cases you have to use an additional box supplied with the barrier. Although some access controllers can do this themselves, for the same money.
Magnetic locks, on the contrary, are desirable to re-enable immediately after opening the door (well, not quite immediately, with a tiny delay) or at least after closing it — otherwise, having slammed, the door may «jump back», and the system, naturally, will decide that this is already the second opening, unauthorized, and now an alarm, a siren, a capture group with machine guns …
There are also additional functions that increase the reliability of protection. For example, protection against code selection. If someone comes with a pack of cards and tries them all in turn, a good controller should not just deny access, but call security. By the way, the situation is far from harmless, imitators of contactless cards or intercom contacts are extremely simple, their schemes are available on the Internet, so any literate schoolchild can build a device for automatic code selection.
Sometimes, to increase the level of security, you want to install a reader combined with a keyboard so that the system does not let in those who simply stole the access card but do not know the correct code. Additionally, such a system can allow a person who is forced to open the door to give a silent alarm signal (for example, if he dials his code plus 3). Do you think that an intruder standing behind you with a gun is from spy movies? Not at all. This is one of the simplest ways to quietly clean out a locked warehouse. Just wait until the guard goes out for some reason and show him convincing arguments why he should let a crowd of robbers in.
Another function that increases security is re-entry control. It can be different and complex, but often the simplest is enough: so that the card does not work on the same reader for a few minutes after passing. This is enough so that those who forgot their pass do not pass through the turnstile at the checkpoint using a friend's card handed back to them, but go and write an explanatory note to the security service.
Now let's move on to more complex configurations.
Many systems allow you to install readers both at the entrance and at the exit. But it turns out that not all of them are able to set permissions for entry and exit separately. To tell the truth, this is rarely necessary, and such permissions almost double the required volume of the stored database, plus it increases the costs of configuring the system. Very rarely does a system support the ability to work sometimes with a free exit (by button), and sometimes (for example, at night) with an exit only by reader.
By the way, when implementing a two-way access point, very often these will actually be two access points: the output relay of one of them will be connected to the input of the other instead of the exit button. In this case, it may turn out that even the simplest functions stop working, such as the control of «whether a passage was made».
An even more complex option is a turnstile. The turnstile has two readers. As a rule, two solenoids allowing passage in or out, but a single «door opening sensor» (in reality, a sensor indicating that the turnstile has been brought out of the resting state, no matter in which direction). Many controllers control the turnstile as if there were two different doors, each with one reader and one lock. And the single «door opening sensor» in this case cannot be connected anywhere. This is sometimes acceptable, but the very simple function of checking whether «there was a passage» will not work. And if the turnstile cannot automatically reset the latch after passage (and almost all turnstiles are like this), then the turnstile will rotate freely for the entire programmed «impulse to the lock» time. And what is the point of a turnstile then, if 20 people can quickly pass through it with one card?
Finally, the gateway. It doesn't have to be a fancy (and very expensive) rotating bulletproof cylinder, which is sometimes found in reputable banks. In important places, a gateway can be organized simply from two doors (vestibule). A gateway, like a turnstile, can guarantee that only one person will pass through at one «access permitted» signal. However, the controller must be able to sequentially open one door, wait until it is closed, and then open the second. Very few controllers can do this. But when it comes to a gateway, you immediately want to add a third reader (biometric) inside and lock in the gateway violators who try to get in with someone else's card. Or at least put scales there and monitor the weight so that two people don't try to squeeze into the vestibule at the same time.