Subtleties of using a long-range identification system.

Subtleties of using a long-range identification system.

We have recently covered some applications of long-range identification systems at sites, in particular for monitoring parking lots, access to premises and entry to parking lots. Today we will look at some more aspects of long-range identification applications using PR-G07 readers, manufactured under the Parsec brand.

Standard Problems…
If you turn the saying «every cloud has a silver lining» upside down, it will be exactly about long-range identification systems. Those who have never installed long-range readers in practice have not stepped on this rake and live in a world of illusions that installing such a reader will immediately raise their rating in the eyes of the boss or customer. However, there have been, are and will be problems. And the main one is the blurriness or smearing of the reading zone, which is determined by the very principles of the readers.
Anyone who has used proximity cards to gain access to premises has noticed that different cards on different readers have a spread in reading range even with ideal orientation. With a reading range of 10-15 cm (we are talking only about good readers — those that require «rubbing» the card are not worth mentioning at all), a spread of a centimeter or two will not affect the operation of the system in any way. Now replace centimeters with meters — you already get a spread measured in meters. Now you need to add the influence of the orientation of the active card or tag, the influence of various kinds of electromagnetic interference, which literally fills the surrounding space to the brim (and mobile phone radiation is also an interference for the reader) — and the spread will be up to 50% of the nominal reading distance.
If we talk about using long-range identification readers indoors, then an extra meter can be practically fatal. Imagine a corridor two meters wide, doors to rooms equipped with «long-range» readers, and people moving along the corridor… Of course, the door will open for the one who wants to enter through a specific door, but how will a standard access system controller react to everyone else passing by? — That's right: the controller will simply go crazy. An experienced installer will say: I will turn on the passage recording mode only after the door opens when the reed switch is triggered. Well, sit down — four! But who will the controller record as passing through the door if there are two or more identifiers in the reader field?
Another consequence of a large spread of the reading zone is the impossibility in some cases (for example, when equipping a doorway) to reliably determine the direction of passage.

…and how to deal with themSo, the problems are known, and this is already part of the success. Although we will immediately slightly disappoint both installers and users of long-range identification systems: in a number of cases, the problems remain insoluble. Such cases include installations in extremely limited space, when it is simply not possible to spread the readers or their antennas at an acceptable distance for operation. In such a situation, it is sometimes more economically advantageous simply not to use such a system, despite all its apparent advantages (especially convenience).
If there is enough space, then several factors will help to optimally configure and set up the system using PR-G07 readers.

Reader Configuration
When used together with standard access system controllers (these are controllers that do not have the function of user-programmable additional processing of read identifiers), the readers take on part of the system's operation logic. This is ensured by the fact that the reader is made dual-channel, which allows for the processing of the read identifier in one of the channels depending on the state of the second channel.
In addition, the readers allow for the identifier processing logic to be linked to signals from external sensors (for example, gate automation sensors), and up to two different sensors can be connected to each channel.
Other features of this type of readers include:
programmable reading range for each channel;
unique anti-collision mode, allowing for the simultaneous monitoring of more than one hundred tags in the reader's field.
Flexible configurable reader logic, depending on the operating mode of the access point or vehicle passage. The principle of using sensors and the internal logic of the reader using the example of entering a parking lot was discussed in the previous article devoted to the use of this equipment. Today we will consider other examples of using PR-G07 together with ActiveTag active tags.

Adaptation of tags
ActiveTag tags are programmed during production for a certain average application. However, even placing the tag in the same place (for example, on the inside of a car windshield) can give very different results. The fact is that any glass is welded with the addition of lead, which largely determines the properties of the glass. And lead, as is known, is a good conductor. In addition, different glass tinting technologies can also affect the reading range of tags in different ways.
This is why, in order to adapt each tag to specific conditions of use, a special programmer should be used, which allows the reading range to be changed within a wide range.
Another feature provided by the programmer is changing the exchange period of the tag with the reader. In the standard version, tags are programmed for an exchange rate of approximately three times per second. However, if you are not going to record cars passing by the reader at a speed of 100 or more kilometers per hour, then the exchange period can be safely reduced to once per second or even lower. The consequence of this will be an extension of the tag battery life before its replacement.

Calculating the tag exchange rate
If it is necessary to record fast-moving vehicles, the tag exchange period with the reader should be adapted to specific conditions, and the higher the vehicle speed, the shorter the battery life. The dependence of the maximum vehicle speed on the reading range and the tag exchange period with the reader is reflected in the table below.

For reliable identification, it is desirable that the tag be read at least 3-5 times per second. For a standard tag, the exchange period is approximately 3 times per second. The table shows that for 5-fold reading (1.7 seconds) at a speed of 100 km/h, it is necessary to have a reading zone of at least 50 m.
Note that the maximum reading area is provided at the maximum output power of the tag (0 dB), and additional increase is provided by using directional antennas with high gain. The PR-G07 reader is standardly equipped with an antenna with a beam width of about 60 degrees and a gain of 6 dB. To increase the reading range, you can use antennas with a 15-20 degree beam and a gain of up to 18 dB. You can buy or order such antennas from almost any supplier of Wi-Fi network equipment.

System installation options
Now that we have covered some of the features of using long-range identification systems in general, let's look at examples of specific configurations at sites.

Small parking lot
This example is based on a real installation in the office of a small European company. It was necessary to provide automatic entry into the office territory for employees' cars. At the same time, the standard radio button of the automatic gate system was used for exit. The general layout of the territory and the installed equipment is shown in Figure 1.

Figure 1. Installation in a limited area.

The main problem was that the internal parking area was very small and it was impossible to clearly ensure the reading boundary between the gate and the parking lot. Moreover, the area is so compact that there were cases of reading the tags of cars parked in the parking lot by the entry channel of the reader, which led to a false opening of the gate.
The problems were solved in two ways.
For exit, the gate was opened by a radio button attached to the exit door of the office, i.e. the employee presses the button when leaving, gets into the car and leaves the area.
For the smooth operation of the entry system, the built-in interchannel logic of the reader is used. When approaching the office, the tag is guaranteed to be read only by the entry channel of the reader, and its code is transmitted to the access controller that controls the gate. After entering the parking lot, the second channel begins to «see» the tag, but this does not lead to a false opening of the exit gate, since the first channel still «remembers» the tag. Further, since the second channel continues to record the tag continuously, its code is not transmitted to the controller. When leaving, when the first channel again records the tag, no response occurs, since the first channel checks this tag in the second channel, finds it there and does not consider the fact of the tag's appearance in its reading field a necessary condition for opening the gate.

Accounting for the movement of dump trucks
This example is also taken from practice. At the quarry, it was necessary to simply record the facts of entry and exit of dump trucks working there; no barrier devices were required according to the conditions of the task.
To solve this problem, we used one PR-G07 reader in the «drive-through» mode. The layout of the equipment is shown in Figure 2.

Figure 2. Accounting for dump trucks in a quarry.

In this configuration, the direction of travel is determined by the reader itself based on the sequence of intersections of the reading zones of the first and second channels and, in accordance with this, transmits the code of the tag attached to the dump truck to the entry or exit channel of the access system controller. Without the use of the built-in logic of the reader, the standard access system controller would hardly be able to determine the direction of movement of dump trucks.
There are many more examples of using the PR-G07 reader in various situations, but the article is too large to do so. We can only say with confidence that the unique capabilities of this product make it possible to solve many problems that cannot be solved using other similar equipment.