Switching devices and elements. Communication in rural areas refers to the telecommunication system of the organization


Federal agency on education of the Russian Federation

Oryol State Technical University

Oryol Technological Institute

Oryol Polytechnic College

By discipline: "Typical elements of self-propelled guns"

Subject: "Switching elements"

Speciality: 220301

The abstract is protected with the following rating:

Supervisor: Garanzha T.S.

SWITCHING ELEMENTS

Purpose. Basic Concepts

Switching elements are designed to enable, disable and switch electrical circuits. Switching usually means performing these three operations. There are switching elements of manual and automatic control. Manual control switching elements are activated by direct mechanical action on their controls. Automatic switching elements are activated under the influence of electromagnetic forces on their drive elements. The main part of such elements is usually an electromagnet; the input signal for them is electricity or tension. Automatic switching elements are used in automation systems and remote control various mechanisms and devices. These are discussed in subsequent chapters in this section.

This chapter covers mechanically driven switching elements. They are used, as a rule, for local control and for signaling the achievement of any intermediate and final positions. According to their purpose, switching elements are divided into two types: for switching power circuits (windings of electric motors, powerful electromagnets, transformers, heaters and other consumers) and for switching control circuits (windings of relay contact equipment, control, regulation and signaling devices). This division is due different meanings currents and voltages in switched circuits, which, in turn, affects the design and overall dimensions. The study of switching elements for power circuits is not our task. We only note that the most widely used for these purposes are switches and switches of the chopping type, providing quick opening and having special devices to extinguish the electric arc.

All switching elements used in control circuits must have the following components: fixed contacts, moving contacts and a control element. In addition, they may have elements for fixation, installation and adjustment, arc extinguishing, etc. The necessary switching elements are selected according to acceptable values current and voltage. But the most important characteristic of switching elements for practice is their reliability, i.e., maintaining operability with a large number of operations.

Switching elements are distinguished by the number of switched circuits (single-circuit and multi-circuit) and by the number of fixed positions, and there are switching elements with self-return initial position, i.e. without fixing the switched position, which may be necessary for a number of control circuits.

Mechanically driven switching elements include control buttons, microswitches, toggle switches, key, rotary, lever and cam switches, as well as limit and limit switches.

Control buttons and toggle switches

Control buttons are devices whose movable contacts move and are activated when the button pusher is pressed. A set of buttons mounted on a common panel constitutes a push-button station. The control buttons used in automation circuits are distinguished by the number and type of contacts (from 1 to 4 normally open and closed), the shape of the pusher (cylindrical, rectangular and mushroom-shaped), and the method of protection against impact environment(open, closed, sealed, explosion-proof, etc.).

Regardless of the design and overall dimensions buttons (Fig. 1, a, b) they all have fixed contacts 1 and moving contacts 6, moved by pusher 3. The external circuit is connected to the button using screw terminals 7. Housing 2 buttons are fixed on the control panel with nuts 4 And 5.

Rice. 1. Control button designs

Electrical parameters The most common buttons are shown in Table 1. Control buttons for general industrial use of the KU and KE series have different designs and pusher shapes.

Table 1. Electrical parameters of control buttons of various types

For switching circuits, electronics are produced special buttons(for example, type VK14-1). Small-sized control buttons are made on the basis of a microswitch of the MP type, which is used as an actuating contact element in toggle switches of the MT1 and MTP types. The durability and reliability of control buttons is assessed by switching wear resistance, which is expressed in the guaranteed number of on-off cycles under load. This option is different for different buttons and operating conditions. For example, for buttons of the VK14-21 type with copper contacts it is 0.25 * 10 6 cycles, with bimetallic contacts - 2.5 * 10 cycles, with silver contacts - 4 * 10 "" cycles. Mechanical wear resistance always exceeds commutation resistance. IN Lately Control buttons with a rectangular pusher shape have become increasingly widespread - they are called keys.

Based on control buttons, pushbutton stations are manufactured containing up to 12 buttons of various designs, assembled on a common panel or in one housing. Such switching devices are called push-button or key switches (Fig. 2).


Fig.2. Push Button Switches

The switch is a dial panel of buttons 1 (or keys) mounted on a common frame 2 and equipped with a locking mechanism, which can be independent for each button (key) or mutually interlocked. The buttons may also have a self-return to their original position or alternating on and off fixed positions. Each button or key switches one or more circuits. Some types of switches are equipped with a special button to return (reset) the switched buttons to their original position. In this case, it is possible to turn on several buttons at the same time. A special feature of these switches is the two-position position (on, off) of each button or key. The required mode or control program is set by dialing the on and off positions of the corresponding buttons (keys). In this case, the position of the buttons or keys (raised or recessed) plays the role of a pointer. Light signaling devices are also used for this purpose. 3 (lamps or LEDs) mounted in the housing of the switch block (Fig. 2). The closed design and the use of high-quality materials (bimetals, silver alloys, etc.) for contacts provide low transition resistance, which is very important when installing these switches in low-voltage and low-current circuits of automation and electronics.

For more powerful automation circuits, toggle switches are used, used as switches, as well as two- and three-position switches. Figure 3 shows the device of a two-position toggle switch. A bridge contact, made in the form of a conductive roller /, closes one of two pairs of fixed contacts 2. The toggle switch contacts are switched by pressing the lever 3, and acceleration of response (instantaneous action) is provided by a spring 4. The rated current of the toggle switch is I and 2 A at a voltage of 220 V, their weight does not exceed 30 g.

Fig.3. Two position toggle switch

To switch multiple circuits at several fixed positions, batch switches are used to select different operating modes. Such a switch (Fig. 4, A) consists of a number of layers - packages 3 (shown separately in Fig. 4, b), inside which there are movable 5 and motionless 4 contacts. Movable contact 5 fixed on an axis 2, rotating with a handle 1 and having a number of fixed positions, and which close the fixed contacts of one of the packages. conclusions 6 fixed contacts are fixed in the switch body. The disadvantage of such packet switches is the low reliability of the sliding contacts.

Cam-type stack switches, in which the electrical circuit is closed by fixed contacts, are more reliable. They have movable dielectric cams, which close the contacts depending on the profile of the cam and the position of the axis. The designs of package switches designed for control circuits allow you to obtain dozens and hundreds of options for various connection schemes with the number of switched circuits up to 24 (12 packages) and the number of fixed positions up to X (every 45, 60 or 90°).

Chapter 15

SWITCHING ELEMENTS

§ 15.1. Purpose. Basic Concepts

Switching elements are designed to turn on, turn off and switch electrical circuits. Switching usually means performing these three operations. There are switching elements of manual and automatic control. Manual control switching elements are activated by direct mechanical action on their controls. Automatic switching elements are activated under the influence of electromagnetic forces on their drive elements. The main part of such elements is usually an electromagnet; the input signal for them is electric current or voltage. Automatic switching elements are used in automation systems and for remote control of various mechanisms and devices. These are discussed in subsequent chapters in this section.

This chapter covers mechanically driven switching elements. They are used, as a rule, for local control and for signaling the achievement of any intermediate and final positions. According to their purpose, switching elements are divided into two types: for switching power circuits (windings of electric motors, powerful electromagnets, transformers, heaters and other consumers) and for switching control circuits (windings of relay contact equipment, control, regulation and signaling devices). This separation is due to different values ​​of currents and voltages in the switched circuits, which, in turn, affects the design and overall dimensions. The study of switching elements for power circuits is not our task. We only note that the most widely used for these purposes are circuit breakers and switches of the cutting type, which provide quick opening and have special devices for extinguishing the electric arc.

All switching elements used in control circuits must have the following components: fixed contacts, moving contacts and a control element. In addition, they may have elements for fixing, installation and adjustment, arc extinguishing, etc. The necessary switching elements are selected according to the permissible current and voltage values. But the most important characteristic of switching elements for practice is their reliability, i.e., maintaining operability with a large number of operations.

Switching elements are distinguished by the number of switched circuits (single-circuit and multi-circuit) and by the number of fixed positions, and there are switching elements with self-return to their original position, that is, without fixing the switched position, which may be necessary for a number of control circuits.

Mechanically driven switching elements include control buttons, microswitches, toggle switches, key, rotary, lever and cam switches, as well as limit and limit switches.

§ 15.2. Control buttons and toggle switches

Control buttons are devices whose movable contacts move and are activated when the button pusher is pressed. A set of buttons mounted on a common panel constitutes a push-button station. The control buttons used in automation circuits are distinguished by the number and type of contacts (from 1 to 4 normally open and closed), the shape of the pusher (cylindrical, rectangular and mushroom-shaped), the method of protection from the environment (open, closed, sealed, explosion-proof, etc. .).

Regardless of the design and overall dimensions of the buttons (Fig. 15.1, a, b) they all have fixed contacts / and moving contacts 6, moved by pusher 3. The external circuit is connected to the button using screw terminals 7. Frame 2 buttons are fixed on the control panel with nuts 4 and 5.

The electrical parameters of the most common buttons are given in table. 15.1. Control buttons for general industrial use of the KU and KE series have different designs and pusher shapes.


For switching electronic circuits, special buttons are produced (for example, type VK14-21). Small-sized control buttons are made on the basis of a microswitch of the MP type, which is used as an actuating contact element in toggle switches of the MTI and MTH types. The durability and reliability of control buttons is assessed by switching wear resistance, which is expressed in the guaranteed number of on-off cycles under load. This setting varies for different buttons and operating conditions. For example, for buttons of type VK14-21 with copper contacts it is 0.25 * 10 6 cycles, with bimetallic contacts - 2.5 * 10 8, with silver contacts - 4 * 10 6 cycles. Mechanical wear resistance always exceeds commutation resistance. Recently, control buttons with a rectangular pusher shape have become increasingly widespread - they are called keys.

Based on control buttons, pushbutton stations are manufactured containing up to 12 buttons of various designs, assembled on a common panel or in one housing. Such switching devices are called push-button or key switches (Fig. 15.2).

The switch is a dial panel of buttons / (or keys), mounted on a common frame 2 and equipped with a locking mechanism, which can be independent for each button (key) or mutually interlocked. Buttons can also have a self-return to their original position or alternating between on and off fixed positions.


assigned positions of the corresponding buttons (keys). In this case, the position of the buttons or keys (raised or recessed) plays the role of a pointer. Light signaling devices are also used for this purpose. 3 (lamps or LEDs) mounted in the housing of the switch block (Fig. 15.2). The closed design and the use of high-quality materials (bimetals, silver alloys, etc.) for contacts provide low transition resistance, which is very important when installing these switches in low-voltage and low-current circuits of automation and electronics.

For more powerful automation circuits, toggle switches are used, used as switches, as well as two- and three-position switches. In Fig. Figure 15.3 shows the device of a two-position toggle switch. A bridge contact, made in the form of a conductive roller /, closes one of two pairs of fixed contacts 2. The toggle switch contacts are switched by pressing the lever 3, and acceleration of response (instantaneous action) is provided by a spring 4. The rated current of the toggle switch is 1 and 2 A at a voltage of 220 V, their weight does not exceed 30 g.

§ 15.3. Batch switches

To switch several circuits with several fixed positions, batch switches are used to select different operating modes.* Such a switch (Fig. 15.4, A) consists of a number of layers - packages 3 (shown separately in Fig. 15.4, b), inside which there are movable 5 and fixed 4 contacts. Movable contact 5 is fixed to the axis 2, rotating with the help of a handle / and having a number of fixed positions in which the fixed contacts of one of the packages are closed. conclusions 6 fixed contacts are fixed in the switch body. The disadvantage of such packet switches is the low reliability of the sliding contacts.

Cam-type stack switches, in which the electrical circuit is closed by fixed contacts, are more reliable. They have movable dielectric cams, which close the contacts depending on the profile of the cam and the position of the axis.

The designs of package switches designed for control circuits allow you to obtain dozens and hundreds of options for various connection schemes with the number of switched circuits up to 24 (12 packages) and the number of fixed positions up to 8 (at 45, 60 or 90°).

There are switches without fixing the switched position - with self-return to the original position. A special feature of these switches is the presence of a locking (key) device, which eliminates uncontrolled switching.

The most common control circuit switches are devices of the PKU2 and PKUZ series. Rated (long-term permissible) current of switches of the PK.U2 series is 6 A at a voltage of 380 V alternating current and 220 V DC, and for switches of the PKUZ series - 10 A at 500 V AC. As can be seen from the technical parameters, such switches are suitable for directly turning on and off quite powerful consumers electricity, for example electric motors with a power of several kilowatts.

Switches of the PU and PE series have smaller dimensions, having rotary drive mechanisms for two or three positions. Among them there is a version with a removable key-handle. Such switches, as a rule, block the supply of voltage to the control circuit and change control modes and methods. At the same time, it is possible to lock the switch both in the off and in its other positions. Rated current of switches of the PU and PE series is 5 A at a voltage of 220 V AC and 1 A at PO V direct current.

Automatic and program control require very complex switching, which requires multi-position and multi-circuit switches (with the number of circuits and positions sometimes reaching several dozen). Structurally, such switching elements are made in the form of two, four (or more) fixed sections mounted on boards, and movable contacts mounted on a common shaft and fixed with a special spring-ball retainer in specified positions.

In Fig. 15.5 shows the most common slide switches of the PP series of single-soldered design for 35 circuits


They provide reliable switching at load currents of up to 1 A of alternating (380 V) and direct (220 V) current circuits.

IN radio-electronic equipment similar packet switches are used - the so-called biscuits. They have from 2 to 11 positions with the number of sections (biscuits) from 1 to 4. In Fig. Figure 15.6 shows a 10-position ASG series switch.

Recently, automation has increasingly used the achievements of microelectronics, for example large integrated circuits. For switching in circuits containing such elements, switches are needed whose contacts would ensure the reliable passage of very weak currents (milli- or microamps) at low voltages (up to 5 V). The switches discussed in this paragraph, as a rule, do not have such properties, since their contacts have significant (sometimes several ohms) transition resistances. In this case, it is preferable to use key switches with bimetallic or silver contacts.

§ 15.4. Travel and limit switches

Track and limit switches are switching elements that are kinematically connected to the working machine and are triggered depending on the movement of the moving part of the working machine. Track switches are triggered at certain intermediate points along the path of movement, limit switches are triggered at the extreme points: at the beginning and end of the path. Travel and limit switches are especially widely used in automated electric drive circuits of various production mechanisms. automatic control drive on certain sections of the track and automatic shutdown in the extreme positions of the mechanism.

Depending on the device that closes or opens contacts, travel and limit switches can be divided into push-button (push-type), lever, spindle and rotary. Switching contacts in these switches is carried out as follows. In push-button systems - by pressing the working part of the mechanism on the rod to which the switch contacts are connected. In lever ones - by the action of the working body of the mechanism on the lever to which the contacts are connected. In spindle ones - by moving the nut along a screw connected through gears to the mechanism shaft. In rotating ones - by switching cam washers connected to the mechanism shaft.

In rod switches, the switching speed of the contacts is determined by the speed of movement of the production mechanism. At low speeds, the mutual movement of movable and stationary contacts occurs slowly, which leads to prolonged burning of the arc that occurs between the opening contacts and their rapid destruction due to melting and increased oxidation. For normal operation of such a switch, the movement speed of the mechanism must be at least 0.5 m/min. And to ensure instant switching of contacts, special spring mechanisms are used, which are released using trigger mechanisms (pawls). Springs are also used to provide the necessary contact pressure. In Fig. Figure 15.7 shows the design of a simple limit switch. It is fixed in such a way that the emphasis on the moving part of the production mechanism is opposite the rod 4. When pressing the stop on the rod 4 the latter presses on the spring 3. When a certain force is pressed, the spring 3 moves to the left, opening the contact 2 and closing contact 1. In this case, the current will flow through another control circuit. External connections of the switch are made by soldering to the terminals: 5 -fixed contact (general); 6 - open contact 2; 7 - closing contact /. Flat spring 3 made of three parts. The middle part is longer than the extreme ones, so it is always in a curved state and tends to press the contacts in their extreme positions (/or 2). The switch is capable of operating in circuits with voltages up to 380 V at currents up to 3 A. The movement of the rod is 0.5-0.7 mm, the required force for operation is no more than 5-7 N. The operation time is 0.01-0.02 s at switching frequency up to two times per minute.

In Fig. Figure 15.8 shows a VK-111 type limit switch with bridge contacts. Contacts are switched by pressing rod 1, and the contacts return to their original position by a spring 2. Using a bridge contact 3 reduces the likelihood of an arc occurring because the circuit is broken at two points. Such switches can operate at a switching current of up to 20 A and a continuous current of 6 A. The wear resistance of the switches is 10 6 operations. Permissible frequency -

600 starts per hour.

In Fig. Figure 15.9 shows a switch with a short response time (torque action). The contacts of such switches switch at a constant speed at a certain position of the production mechanism, regardless of the speed of movement. Therefore, they are used at low speeds (up to 0.5 m/mi) or when increased operating accuracy is required (up to 0.05 mm).

When pressing the stop on the roller 1 lever 2 rotates and presses against a set of coil springs 3, instantly acting on the leash 4. The leash turns and the roller 10, compressing the spring 11, moves along the plank 9, occupying a position to the right of the bar's rotation axis 9. At the same time the dog 6 the contact bridge is also retracted under the action of a spring 11 and roller 10 changes to another position, opening contact 7 and closing contact 8. After the stop moves away from the roller, 1 leash 4 and the contact bridge returns to its original position under the action of a spring 5.

In some cases, multi-position three- and five-contact sensors are used, sequentially controlling several control circuits. The designs of such sensors are more complex, and they are much more expensive than two-pin ones.

The considered travel and limit switches have relatively low reliability associated with increased wear of the contact pair. Higher reliability is ensured when using non-contact sensors (for example, inductive or photoelectric types), the instantaneous response of which is ensured using electronic circuits.

Switching– the process of closing, opening and switching electrical circuits.

Switching unit (CU)- an integral part of the telecommunication network on which switching is carried out. The CU is connected to each other by trunk lines (local or long-distance).

Switching station (station)- KU, which includes subscriber lines. Subscriber– a person using a subscriber device to transmit and receive information.

Channel (line)– set technical means(line and station, providing connection and transmission of information between two adjacent CUs, as well as between the subscriber device (stationary telephone, teletype, computer, etc.) and the station.

KU– a device designed to receive, process and distribute incoming information.

To perform its functions, the CU must have:

  1. Switching field (CF), which is intended for switching incoming and outgoing lines (channels) for t transmission of information.
  2. The control device (CD), which ensures the establishment of a connection between the incoming and outgoing lines in the control panel, as well as the reception and transmission of control information to the equipment for receiving and transmitting control information, includes: registers (PN sets), checkpoints, and converters.
  3. Linear LC sets (these are AK and KSL), which receive and transmit linear signals (interaction signals)
  4. Cord sets (CS) are designed to power SLT microphones and issue service signals
  5. Cross – device for input and output of lines.
  6. Power supplies.
  7. Alarm devices US
  8. Devices for recording load parameters (number of messages, losses, duration of exercise, etc.)

The control system of communication networks is classified according to a number of characteristics:

  1. By appearance transmitted information: telephone, telegraph, broadcasting, telecontrol, data transmission, etc.
  2. According to the method of servicing connections: manual, semi-automatic, automatic.
  3. According to the place occupied in the telecommunication network: regional, central, hub, terminal, transit stations, UVS, UIS.
  4. By type of communication network: long-distance, urban, rural, institutional.
  5. By type of switching and control equipment: electromechanical, mechanoelectronic, quasi-electronic, electronic.
  6. According to the systems of switching equipment used: DS, coordinate, machine, quasi-electronic, electronic.
  7. By capacity, i.e. by the number of incoming and outgoing lines, included subscribers: small, medium, large capacity.
  8. By type of switching: operational, cross, mixed.
  9. According to the method of channel separation: spatial, spatial-temporal, spatial-frequency.
  10. According to the method of transmitting information from the transmitter to the receiver: circuit switching nodes, message switching nodes, packet switching nodes.

There will be no decoding of the information received, since this is precisely the task and object of our study in the future.

4.2. Construction of single-link switching blocks

Single-link switching is called one in which the input and output of the CS (switching system) are connected through one switching point.

KB– a set of switching devices having all or part of common outputs and combined general parameters(this concept is practically not used in DS ATS)

Load Sources– lines through which the TF load is supplied to the input of the switching system.

Bunch of lines– a set of lines connected to the output of the CS and available to a certain group of load sources.

Load group– a set of load sources that have access to a specific bundle of lines, for example, connected in a given direction of the search stage (to all inputs of a given KB).

Search stage– part of the CP of a given CU, consisting of interconnected KBs of the same type. KB has certain structural parameters. They can be obtained by combining the inputs and outputs of switching devices in a certain way.

The KB is characterized by the following structural parameters: the number of inputs and outputs, the number of PLs, D-availability of inputs in relation to outputs, the number of links (switching points), the total number of switching points for building a block, the conductivity of lines switched in the block, the number of simultaneous connections in the block .

When building a KB, you can perform the following operations: combining inputs, combining outputs, serial connection switching devices (organization of multi-link circuits). Operations can be combined.

In a CS, the inclusion of outputs in relation to inputs can be fully accessible or NAP.

PD switching on- this is when any input of the CS can be connected to any free output

NAP inclusion– this is when the input can be connected only to a part of certain outputs of the block.

D availability– the number of CS outputs with which the CS input can receive a connection (the number of CS outputs in a given direction - for the GI stage)

Direction- this is a bundle of lines, along any of which you can arrive at the required commutation point.

Merging inputs:

Switching parameters n x m
n - input
m – output

Design bureaus can be built on the basis of any switching devices Shi, DSHI, MKS, MSF, etc.


The result is a KB with parameters 1x2m, each input has access to 2m outputs, therefore D = 2m

Symbols of the ISS on the diagram:

Parameters n x 2m

Increasing the number of outputs and D by combining inputs requires an increase in the volume of equipment, i.e. increasing the number of switching devices.

Output merging

to m
D = m

The inputs of all switching devices have access to the same group of outputs. The maximum number of simultaneous connections in such a KB is determined by the number m, if k > m, or the number of inputs k, if k< m .

In addition to the line switching function, KB can perform other functions, for example:

What was discussed above is practically switches.

Switch- this is the simplest single-link fully accessible KB, in which any input has access to any output.

The disadvantage of single-link CBs is that to create a CS with parameters n x m, n × m switching devices will be required - a lot: for example, 100x100, MKS type 10x10 - you need 100 such MKS (unthinkable)

4.3. Single-link search stages

Search stage– part of the control panel for the entire set of inputs of which there is access to the same directions that combine the outputs.

The CP is built from individual KBs, which are then combined into search stages.

There are several types of search stages: preliminary, group, linear and register search stages. In accordance with this, SI can operate in free, group and linear (forced) search modes.

4.3.1. Search modes

  1. Free search mode – when there is no reception of address information (dialing information) and the incoming line is provided with any free channel (output) from among the available ones.

    In this case, the number of directions H = 1, and D = M

    The PI and RI stages operate in this mode.

  2. Forced search mode (linear search) - when the search is performed under the influence of received address information and incoming channel a specific outgoing channel is represented, therefore H = M, and D = 1

    The LI stage operates in this mode.

  3. Group search mode - when the search for a certain direction is carried out under the influence of address information, i.e. in the forced search mode, and the output in a given direction is in the free search mode. That. an incoming channel is given any free outgoing channel in a certain direction, therefore

    1 < Н < М, а Д > 1

    The GI stage operates in this mode.

  4. Some systems have combined search stages. For example, in ATSC, the AI ​​stage combines the PI and LI stages, but only one connection can be established at a time, so for of this connection either free or linear search mode is performed.

4.3.2. Stage LI

A single-link LI stage can be built using DSHI-100. The maximum capacity of a station built in this way can be equal to 100 (no more)

In this case, each AL has its own individual DSHI. The AL is connected to the brushes of its finder and is also connected to the corresponding contacts of all 100 finders of this automatic telephone exchange. Pamels of the same name in decades of the same name. are parallelized and connected to the corresponding AL. AK is used to receive a call signal from a subscriber and coordinate 2-wire subscriber lines with multi-wire lines of station devices. To establish a connection, the subscriber must dial a 2-digit number. According to the first digit, the brushes rise to the required decade (selection of ten), and according to the second in this decade, they select the desired pamel (selection of one). Consequently, both the lifting and rotation of the brushes will be forced, and the search mode at the LI stage is called linear. This method of construction is uneconomical, because it requires big number dear seekers (for each subscriber).

4.3.3. Stage PI

During operation, it was found that 10-15% of connections from the total number of subscribers on a PBX may be required at the same time (on a PBX for 100 subscribers, the maximum number of simultaneous connections is 50, but in reality it is even less - 10-15). Therefore, it is enough to have 10 - 15 DSHI at the LI level, but all 100 subscribers should be able to use them.

Then each subscriber can be assigned an individual LI, which is called a predictor, and outputs to the LI can be included in its contact field.

This is a direct pre-search mode (there is also a reverse pre-search mode) and line finders become group devices. Their number depends on the load.

a) The process of establishing a connection with direct pre-search goes like this: when the subscriber picks up the handset TA (calling the station), the PI brushes begin to move, searching in their field for an exit to a free this moment LI (free search mode). After seizing the LI from the station, the subscriber receives a “station response” and begins dialing a 2-digit number. The first digit causes forced lifting of the brushes, the second – forced rotation and then access to the called subscriber’s telephone station.

Simplified diagram

That. The PI stage allows you to create a more economical automatic telephone exchange scheme, because at a cost of 100 SHI + 10-15 DSHI cheaper than 100 DSHI.

Through the PI stage, the AL is connected to the station devices (LI).

b) With reverse pre-search, a cord pair is formed - IV - IL, the number of which = 10-15 per hundredth group.

IV - call seeker

AL is repeatedly included in the field of all IV and LI. When the subscriber picks up the handset, the “busy” signal arrives at the call center and is marked with the corresponding potential in the IV field. Starting device The PU activates the free IV, which searches for a line in its field caller, and from the LI “hard” connected to it, the subscriber receives a “station response” and begins to dial a 2-digit number. In the forced search mode, the LI brushes find an exit to the called subscriber's telephone station.

IV operates in a free search mode, which is called pre-search (pre-search)

The maximum capacity of an automatic telephone exchange with the PI and LI stages can be = 100 numbers, which is due to the capacity of the LI field.

4.3.4. GI level

Since increasing the capacity of the automatic telephone exchange by increasing the contact field of the seeker is impossible, the principle of group search is introduced, which is implemented with the introduction of the GI stage.

One GI stage increases the capacity of the telephone exchange by 10 times (by an order of magnitude), since at the stage we have 10 directions (10 decades), each of which connects 10 lines to the 100th capacity LI group, hence 100x10 = 1000 numbers.

If there are 2 levels of GI, then the capacity = 100x10x10 = 10000 numbers

The search mode at the GI stage is group, i.e. lifting of brushes is forced, rotation is free.

To implement the GI, 1 digit of the subscriber number is used.

Example: What is the capacity of an automatic telephone exchange with 2 stages of GI?
100x10x10=10000 numbers

What is the significance of the number dialed by the subscriber?
2(LI) + 1(IGI) + 1(IIGI) = 4

DSHI is used as switching devices at the GI stage of the automatic telephone exchange.

So, single-link search stages are used on automatic telephone exchanges of the DS type (mostly), because RI on ATSC too.

Chapter 7. Principles of building switching systems.

§ Structure and classification of switching nodes

Under switching refers to the closing, opening and switching of electrical circuits. Switching is carried out at switching nodes. On telecommunication networks, through switching, subscriber devices are connected to each other to transmit (receive) information. Switching is carried out at switching nodes (CU), which are components telecommunication networks.

Subscriber devices of the network are connected to the KU by subscriber lines. CUs located on the territory of one locality are connected by connecting lines. If CUs are located in different cities, then the communication lines connecting them are called intercity or intrazonal.

The switching node into which subscriber lines are connected is called switching station or simply station. In some cases, subscriber lines are included in substations. A person who uses a subscriber device to transmit and receive information is called subscriber. To transfer information from one network subscriber device to another, it is necessary to establish a connection between these devices through the appropriate nodes and communication lines. To make the connection, switching equipment is installed at the switching nodes.

The set of line and station facilities designed to connect terminal subscriber devices is called connecting path. The number of switching nodes between connected subscriber devices depends on the network structure and direction of connection.

To implement the required connection, the switching node and the subscriber device exchange control signals.

At the switching node, the connection can be established for the time necessary to transmit one message (for example, one telephone conversation), or at long time, exceeding the transmission time of one message. The first type of commutation is called operational, and the second - cross (long-term).

Switching node (CU) is a set of equipment designed to receive, process and distribute incoming information. The most typical example of a control system is a switching station, which includes subscriber and trunk lines. A simplified block diagram of the switching node is shown in Fig.

Rice. Switch node structure

To perform its functions, the CU must include the following: main blocks:

Commutation field (KP) - is a set of switching devices with the help of which the connection of subscriber and trunk lines included in the station is ensured.


Control device (CU) - designed to control the process of establishing connections. It includes equipment for receiving, generating and transmitting control information. Based on the information about the number of the called subscriber or the direction of communication received from the call source, the CU includes the corresponding elements of the switching field, resulting in a connection between the corresponding input and output.

Trunk blocks (BSL), through sets of trunk lines (CLS) of which communication lines from (to) other CUs are connected via analog or digital trunk lines (CL). When using unidirectional trunk lines, incoming and outgoing trunk lines are separated.

Subscriber line blocks (BAL), through subscriber kits (SK) of which subscriber lines are connected to the station.

The CU equipment also includes additional blocks :

Cross - line input and output device.

Cord kits (ShK), which in coordinate-type automatic telephone exchanges serve to power telephone sets, as well as receive and send service signals during the process of establishing a connection.

Power supplies.

Equipment operation monitoring devices.

Load parameters metering devices.

The following types of connections can be established at switching nodes:

intra-station - the connection is made between subscribers of this telephone exchange;

outgoing - a connection is established at the initiative of a subscriber of a given station with a subscriber of another station through a connecting line;

incoming - a connection is established with a subscriber of a given station by a call received via a trunk line from another station;

transit - at this station two connecting lines are switched in order to connect subscribers of other stations.

Switching nodes of communication networks are classified according to a number of criteria:

by type of information transmitted (telephone, telegraph, broadcasting, data transmission, etc.);

by connection servicing method (manual, automatic);

by place occupied in the telecommunication network (district, central, hub, terminal, transit stations, nodes of incoming and outgoing traffic);

by type of communication network (urban, rural, institutional, intercity);

by type of switching and control equipment (ten-step, coordinate, quasi-electronic, electronic);

by capacity ,T. e. by the number of incoming and outgoing lines or channels (small, medium, large capacity);

by switching type (operational, cross-country);

by channel separation method (spatial, space-time);

by switching method (circuit switching, message switching, packet switching).

To carry out switching (connection) of lines (or channels) and control the connection establishment processes on the PBX, switching devices are used.

Switching device (KPR) is a device that provides an abrupt change in the conductivity of electrical circuits for a certain period of time. There are switching devices contact And contactless.

In contact devices, conductivity changes by closing and opening contacts included in the electrical circuit. In non-contact devices, a change in conductivity is achieved by changing any parameter (resistance, inductance or capacitance) of one of the elements of the electrical circuit. The conductivity of electrical circuits in the switching device is changed switching element (CE).

Lines with different conductivity (two-, three-wire, etc.) can be connected to the switching device, so their switching is carried out by several CE, which are combined into switch group. In this case, the switching elements switch simultaneously under the influence of the control signal.

According to the control methods, KPR can be divided into manual and automatic switching devices. Devices manual switching managed mechanical impact person (keys, push-button switches, telephone jacks and plugs). Devices automatic switching controlled by electrical signals.

Depending on the number of input and output lines, a different number of switching groups can be installed in a switching device. A set of switching groups that provides switching of inputs and outputs is called switching field of the device.

The location of a switching group in the switching field of a device (or in a switching block built from several devices) is called commutation point.

To switch electrical circuits, devices are used that provide two stable states of their switching elements (or groups). In this case, the electrical circuit passing through the CE is open in one state (i.e. closed state), and in the other it is closed (open state).

Switching devices differ from each other in structural and electrical parameters.

TO structural parameters include: number of inputs n, number of outputs m, accessibility of entrances D in relation to outputs, the number of simultaneously switched electrical circuits (conductivity), memory property. The derivatives of these parameters are the total number of switching points T,the number of switching groups and the number of switching elements, as well as the maximum number of simultaneous connections.

TO electrical parameters switching devices include: the resistance of the switching element in the closed (open) state and the open (closed) state, the ratio of which is called commutation factor ; time of switching CE from one state to another; insertion attenuation into the conversation path; noise level; supply voltage; the amount of current required to switch the CE; power consumption.

Some switching devices have property of memory ,those. the ability to maintain operating condition after the control input is stopped. This allows you to reduce energy consumption to maintain the operating condition of the device. To return the device to its original state, a new control action is required.

The switching devices currently used can be divided into four types according to their structural parameters:

1. Switching devices such as relays (1 x 1) have one input and one output.

2. Finder type switching devices (1 x m)have one entrance n= 1 and m exits.

3. Switching devices of multiple type connector n(1 x m) have n entrances and nm exits.

4. Connector type switching devices (n x m)have n entrances and m exits.

By means of switching devices, switching blocks, search stages and the switching field of automatic telephone (telegraph, etc.) stations and nodes, control devices, linear and service sets are built.


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