2 x wire communication line. The principle of signal transmission over a two-wire communication line. Construction of analogue addressable security systems based on the S2000-KDL controller

The equipment that transmits black and white or color video over twisted pair (two-wire communication line) consists of a transmitter and a signal receiver. With the help of such a set, a video signal over a twisted pair cable can be produced from a video camera to a VCR (or any similar monitor) at a distance of more than 1500m.

The principle of signal transmission over twisted pair is that the input signal coming from the video camera is converted by the video image transmitter at the transmitter output into two analog antiphase signals.

Two-wire communication line ( twisted pair) connect to the output of the transmitter "A" and "B". The other side of the twisted pair is connected to the signal receiver. Similar inputs, designated "A" and "B", have the input of any receiver. The video signal arriving at the inputs of the receiver is attenuated. Any signal receiver has a sufficiently large gain for the signals that arrive at its inputs and are antiphase.

For your information: network cables Twisted pair connectors are connected to 8P8C connectors, which are often confused with RJ-45. You can see real RJ-45 network cables on the site sokol.ua. This is the online store of household appliances "Sokol".

Also, signal receivers have a large coefficient of suppression of common-mode signals, which are also fed to inputs "A" and "B". Thus, the receiver automatically amplifies the antiphase signals transmitted by the transmitter by the set gain.

At the same time, the suppression of common-mode noise, which was directed to the communication line, is automatically performed. Thus, at the input of a video monitor or a video tape recorder from the output of the receiver, there is already a standard video signal, "cleaned" of interference.

High-quality receivers and transmitters have special amplifiers that provide the necessary parameters (signal processing speed, the required differential gain and common-mode suppression, received at the input of the receiver, signals) by matching the communication line with the transmitter and receiver.

Electromagnetic interference resulting from a lightning discharge is also an induced interference and will be automatically suppressed by the receiver circuitry. A more reliable option would be a receiver and transmitter that have built-in lightning protection circuits, since the induced interference can reach high voltage values, which can damage the equipment.

Previous publications:

Construction of analogue addressable security systems based on the S2000-KDL controller

Controller two-wire line communication S2000-KDL is one of the main elements of the address-analogue subsystem Bolide "Orion". The device constantly monitors all devices connected to it with further signal transmission via RS-485 to the S2000 / S2000M console.

Up to 127 different addressable devices are connected to the S2000-KDL address loop, ranging from security and fire detectors to flow meters and relay modules. However, it should be noted that some devices occupy not 1, but several addresses in the system at once. Therefore, it will be more correct to count not the devices, but the addresses they occupy. This will avoid overloading the loop and incorrect work the controller itself.

The ring topology of the loop of the device significantly increases the reliability of the system, since in the event of a short circuit or a break in the loop, the address line will simply be divided into 2 parts, while remaining fully operational. In this case, all devices in the system (except for the damaged ones) will continue to work as usual. In addition, it is possible to create branches from the main line with the connection of conventional devices to it. For this, special address expanders for 1 or several devices are used.

To protect the addressable loop and devices from short-circuit, branching-isolating blocks Breeze and Breeze isp.01 are installed in the loop. The devices allow you to cut off the short-circuited sections of the addressable loop, thereby blocking further damage to the system. Also, using BRIZ, it is possible to create a loop with a tree topology. The device is placed in the place of the branch and in the event of a short circuit, it cuts off the entire branch completely.

The S2000-KDL controller is also equipped with a circuit for connecting readers using the Touch Memory or Wiegand interface, with which you can control the controller's inputs.

Based on the S2000-KDL controller, it is also possible to organize security systems for hazardous areas. In this case, the S2000-BRShS-Ex signaling loop expansion unit is used, which provides protection at the level of an intrinsically safe circuit. The device is installed outside the protected area and monitors 2 intrinsically safe loops with relaying information to the S2000-KDL.

S2000-KDL operates exclusively under the control of S2000 and S2000M network controllers. The device constantly exchanges data with them, transmits alarm messages to the consoles and executes commands received from the consoles via RS-485. Transmission of notifications is carried out with reference to date and time (internal clock with synchronization function).

Since the controller communicates with control panels and AWPs via the RS-485 interface, there is no need to install all equipment in one room. This feature makes it possible to build distributed systems in which S2000-KDL devices are placed as close as possible to the controlled areas. In this case, control is carried out from a remote control room or fire station of the building. Such systems can significantly reduce the cost of cable products, simplify and speed up installation and maintenance. cable lines and equipment.

DPLS assumes the use of a connection between addressable devices (AC) and the controller "S2000-KDL" of the "bus" type (see the figure below), when all ACs are connected by one pair of wires ("DPLS +" and "DPLS-"). No terminating resistors are required.

It is allowed to connect up to 127 devices with a typical total current consumption of 64 mA to the DPLS (maximum total current consumption is not more than 100 mA). For example, the current consumption of most addressable devices, for example, "DIP-34A" is 0.5 mA, 127 detectors will consume 63.5 mA, which is less than the boundary 100 mA. Accordingly, 127 DIP-34A detectors can be connected to one S2000-KDL.

When calculating the length of the DPLS, to ensure the stable performance of the AU, the following must be taken into account:

• the difference between the voltage at the input contacts of the AC and the output voltage of the controller should not exceed 2 V;
• the resistance of the line from the controller to the AC should not exceed 200 Ohm.
• the total capacitance of the wires should not exceed 0.1 μF (100 nF).

For example: the current consumption of 127 DIP-34A detectors is 63.5 mA, for simplicity, let's imagine that all detectors are installed at the end of the line (boundary condition). A voltage drop of 2 V will be generated with a DPS resistance of approximately 30 ohms. For a section of 0.75 sq. mm, under the above conditions, the length of the DPLS will be ≈ 600 m, and for a section of 0.9 sq. mm ≈ 700 m. In reality, the load on objects is distributed in nature and a voltage drop of 2 V will occur at large distances, but the line resistance to the remote control unit should not exceed 200 Ohm.

There may be branches in the DPLS, but the total capacity of the wires must be taken into account (no more than 0.1 μF).

It is desirable to use a twisted pair of wires as a two-wire communication line.

For the safety of the exchange between the controller and the AU in the event of a DPLS malfunction (short circuit, open circuit), you can use the BRIZ branching-isolating blocks, as well as organize the DPLS structure in the form of a “tree” or “ring”.

At the same time, up to 40 short-circuit insulators "BRIZ" can be connected to the line without additional calculations.
When calculating the length of the DPLS, to confirm the correct cable cross-section and optimize costs, you can use the following technique:

1. DPS is divided into sections, for example, from the controller to AU1, from AU1 to AU2, and so on up to AUn (n is the number of connected AUs). For each section, the values ​​of the resistances R1 ... Rn are calculated.
2. The voltage drop U1 in the first section with resistance R1 is considered taking into account the total current consumption of all the sections connected after this - from AU1 to AUn.
3. Further, the voltage drop U2 in the second section with resistance R2 is considered, taking into account the total current consumption of all connected after this section - from AU2 to AUn.
4. The calculation of the voltage drop in the sections of the circuit is carried out until the last AUn.
5. As a result, it is necessary to sum up the obtained values ​​of voltages U1 ... Un, resistances R1 ... Rn and electrical capacitance of the wires - the obtained values ​​should not exceed those indicated in the table below.

This table shows the maximum values ​​of the DPS lengths for various parameters of the cable cores and the total load used. The table allows, without additional calculations, the use of cables with the presented core parameters for specified values current consumption of addressable devices with arbitrary distribution of AC over the DPS.

Maximum values ​​of DPS lengths, km:

* - the value of the length of the DPLS is limited by the total electrical capacity of the cable

For the convenience of design, the "Program for calculating the DPLS" is posted, which allows you to select the optimal cable for the developed DPLS topology or check the correctness of the choice of cable