In a number of life situations, for example, when a client and a cashier communicate at a train station, in a bank, at a gas station, etc., they are helped by an intercom. Indeed, in these cases it is unlikely to be able to talk without such a technical intermediary. In addition, in production or in the office there is always a need for remote communication between the director and the secretary, the boss and subordinates, which is also provided by similar devices called intercoms or interphones abroad.
Intercom: general characteristics
The first thing to note is the assignment of all intercoms of the class in question to wired communication devices. Microphones and loudspeakers on both sides of the separating speaking partition are connected by electrical wires. Even if such a device is called "wireless" (abroad, the English term wireless is used), this is a very conditional name, since 220 V mains wires are used to transmit the audio signal.
If the voice message is played by a stationary speaker, thensuch a speakerphone is commonly called an intercom. If subscribers have an interphone instead of the usual handsets.
Typical intercom is a simplex device, i.e. subscribers cannot speak at the same time. Interphones are always duplex intercoms, like a regular telephone.
Both types of devices can be either single (for two subscribers) or multichannel.
The latter can be built either according to a radial scheme with one central and many subscriber consoles, or according to a "common bus" scheme with an arbitrary number of subscriber consoles of the same level.
Two-wire communication lines for intercoms and interphones
When the industrial production of equipment for wired intercom systems began in the early 70s of the last century, it required the development of a single standard, a description of the electrical and logical properties of the communication channel included in any intercom for the compatibility of equipment from different manufacturers.
The standard that soon appeared described a three-wire communication line, in which the actual audio signal is transmitted over two wires, and the third wire is the “plus” of the line power (the common wire is one of the audio wires). Such a communication line played the role of a “common bus”, to which all equal subscribers were connected, that is, the speaker at the moment was heard by everyone. Informally, this type of organization of the intercom was called party line, which means "shared line".
However, another name has taken root better - a two-wire line (two wire, TW). It is due to the fact that in a three-wire line only two wires are used directly for sound transmission. It should be emphasized that the term party line does not define the applicable communication standard, but only denotes the principle of its organization - "everything with everyone." But any two-wire intercom could only work on this principle. As a result, it began to be associated only with them, although the party line can be organized using any (for example, four-wire) communication standard.
Modern modifications of TW lines of intercoms and interphones
Despite its considerable age, two-wire (more precisely, three-wire) communication lines continue to be widely used in modern devices. As a rule, they are found in three modifications.
Thus, the well-known manufacturer Clear Com uses in its equipment a line with one common wire for power and audio signal, one signal wire and one power wire.
The second modification, used by Audiocom, includes a pair of audio wires, each of which carries power, and a common wire.
And finally, the third modification - with one common power wire, one wire for the first signal and power, and a wire for another signal.
Four-wire communication lines
In some modern intercoms and interphones for organizing noise-proof duplex communicationthe received and transmitted audio signals are galvanically isolated from each other, i.e. there are two separate signal wires and two common wires in the communication line. In such a four-channel line, power is transmitted through signal wires. At the same time, power supplies of modern devices are characterized by a very low level of (own) interference they create.
Components of intercoms and interphones
These include power supplies, central consoles (for multichannel intercoms with radial organization), subscriber kits (console, outdoor panels), connecting cables, etc.
The DC power supply is usually centralized. However, some subscriber consoles (especially those remote at a considerable distance) may have their own power supplies. Many intercoms are connected to the mains supply, but there are devices powered by two or three 9-volt batteries in series.
Subscriber kits are mainly available in three versions:
- with handset;
- in the form of a call panel "speaker-microphone";
- with headset and speaker combination;
- in the form of a handset.
Their design can also be represented by wall or desktop options. Typically, subscriber kits are equipped with a button (switch) for turning on the microphone (the “Transfer” button), sometimes combined with the “Call” light indicator, and a telephone volume control (in the version with a headset). The subscriber kit in the form of a calling panel (the “speaker-microphone” option) usually does not contain controls.
Intercom "client-cashier"
To ensure communication between a client and an employee of an enterprise (manager, cashier, administrator), a special type of “client-cashier” communicators has been created, since they are most widely used in cash desks of banks, cultural facilities, air, auto and railway stations. Such loud-speaking intercoms occupy an intermediate position between intercoms and interphones, since they are usually duplex, but can be switched to simplex communication mode by the cashier. This is necessary, for example, so that he can consult with his management about the problems of the client, without transferring this conversation to his side. At the same time, the client himself at the checkout can be heard.
Features of voice transmission in "client-cashier" devices
The cashier's workplace is usually reliably soundproofed from the room where the customers are. Therefore, for such devices it is important to transmit the client's speech with maximum filtering of extraneous noise.
Manufacturers deliberately narrow the spectrum of the transmitted signal to the frequency band from 100 Hz to 8.2 (sometimes 9.5) kHz, which is known to fall any human voice. Higher frequency sounds only distort speech, making it difficult to understand.
Usually, specialdigital signal processing algorithms implemented by electronic microcircuits of audio processors, for example, from Motorola. Due to the accuracy and speed of signal processing, such a digital intercom transmits even the first phrase clearly, without “swallowing” the first sounds.
Single-channel intercoms
Such an intercom has the main electronic equipment in the console on the side of the cashier. On the client side, only a remote panel with a speaker and a microphone is mounted. In order to protect against vandals, the speaker is covered with a metal (usually aluminum) cover. Depending on the operating conditions, the customer's panel can also be wind- and waterproof versions with a call button, usually made in the form of a membrane, which prevents moisture from leaking inside.
If several cashiers work simultaneously in the cash register, it is preferable to equip their workplaces with "client-cashier" systems with headphones or a headset. At the same time, the speech of colleagues will not distract the attention of any of the cashiers, who are focused only on their customers.
Multichannel devices
The gas station cashier (or the central security post of the enterprise) must have communication with several anti-vandal client panels located in different places on fuel dispensers (or peripheral posts). Therefore, the central console must be multi-channel, and at the filling station it must also ensure the performance of dispatching functions by transmitting loud announcements. To do this, it must have a line output connected to a sound amplifier,related to the speakers.
The multi-channel intercom "client-cashier", including communication lines with fuel dispensers and a public address subsystem, controlled from a single central control panel of the gas station, significantly speeds up customer service, and also allows the cashier to inform the refuelers of the necessary information.
Organization of a multichannel intercom
So, what kind of equipment, besides the central console and outdoor panels, includes a multi-channel intercom? Its scheme contains the included switch block. It is connected by a four-wire wire line to the central console. Each call panel is connected to the switch unit with a separate wire.
The central console of the device contains a set of digital buttons for selecting call panels. In order to make the cashier's messages clearly audible in the conditions of the gas station, these panels provide for the output of his voice to the speakerphone through an external amplifier and loudspeakers, made in the 2nd category of execution - "Work under a canopy".
Features of intercoms with speakerphone
The hands-free intercom (for gas stations and other facilities) is designed with some design features in order to simplify the communication of the cashier with customers and refuelers. To ensure communication between the cashier and interlocutors at a distance of several tens (or even hundreds) meters from the console, the microphone of his console must be highly sensitive and have wind protectionfor high speech intelligibility regardless of the source of wind noise (e.g. fans). In order to confidently parse the speech of interlocutors at a high noise level, the central console and outdoor panels are equipped with loudspeakers made of Mylar with a high specific area of diffusers.
Popular Commax intercoms
One-channel intercom Commax VTA-2D type "client-cashier" provides duplex communication (without the need to press the "Transmission" buttons). It consists of two identical subscriber sets in the form of "speaker-microphone" calling panels in gray plastic cases. There are wall and desktop execution of panels. It is powered by a 12 V DC source with a consumption of no more than 3.5 W. Its cost is about 1700 rubles.
Also, a single-channel duplex device Commax DD-205 of the "client-cashier" type contains a cashier's console with a flexible microphone mount, electronic adjustment of its sensitivity, light and sound indication of adjustments. An anti-vandal client panel is included in the package of the device. The device is controlled by the Motorola audio processor. Its cost is about 6,000 rubles.
