RS-485 is a type of transducer thatis used in industrial networks. It is also used in differential lines. The most common are modifications for USB-connectors. The principle of the element is built on data transmission by sending low-frequency pulses.
Differents between themselves in the firstturn on the output resistance parameter. It should also be noted that the models are manufactured with different data rates. In order to understand them in more detail, it is necessary to consider the connection scheme for the modification.
Standard connection diagram of the converter
Conventional wiring diagram of the converterincludes self-regulating resistors, as well as an expander. The thyristor is most often used in a switched type. In order to avoid overloads from the network, the plates are applied. In some cases, electromagnetic-type kenotrons are installed to transmit the signal. In total there can be up to five capacitors in the circuit. On average, the output impedance does not exceed 5.5 Ohms. If we consider the industrial interface RS-485 with galvanic isolation, then a pulse expander is used there.
Model with a speed of 100 bits per second
The converter of the RS-232/485 interfacetype is connected exclusively through the transceiver. In this case, the maximum length of one segment does not exceed 1200 nm. On average, the current consumption parameter is equal to 130 mA. If we consider an Ethernet RS-485 converter without expanders, then it uses a buffer amplifier.
Calculated devices for connection no more thanfive transceivers. In this case, the stability of the signal depends on the current carrying capacity. The RS-485 interface cable provides a logic level of 200 mV. The sensitivity of the cascade depends solely on the type of transceiver.
Devices 300 bits per second
Modifications of this type are calculated, as a rule,to support no more than five transceivers. For half-duplex communication, the devices work well. The elements are connected most often through the main amplifier. In total, no more than three capacitors are used in the circuit. On the average, the rate of signal rise in converters does not exceed 1 V per microsecond. Expanders are only used in impulse type. If we consider the RS-422/485 (interface-converter) for modem cables, then it uses an electromagnetic kenotron. Interference in such circuits is observed quite often. It should also be noted that the level of the logical unit is 150 mV on the average.
Models 600 bits per second
Interface converter RS-485 USB of this typeused for modem cables. The maximum segment length in this case is 1300 nm. For bidirectional data transmission devices are suitable well. On average, the sensitivity of the cascade in the transducers does not exceed 210 mV. The rate of rise of the signal is about 1.2 V per microsecond.
The modification can be connectedthrough a buffer amplifier or a resistor. If we consider the first option, then in this situation we can not do without a wire thyristor. It is also important to note that the capacitor is only suitable with an overlay. If we consider a converter-interface RS-485 USB with resistors, then it uses a electromagnetic-type kenotron. In this case, the output impedance of the system fluctuates around 4.6 ohms.
Models for 10 transceivers
Transmitters for 10 transceivershave a high output resistance parameter. Suitable devices of this type are the most for bidirectional data transmission. The average current consumption parameter is 230 mA. The data transfer rate does not exceed 130 bits per second. For automated systems, the models are ideal.
The rate of signal growth in converters is notexceeds 1.3 V per microsecond. The sensitivity of the cascade in this case is insignificant. Direct connection of devices occurs through resistors of a regulated type or an expander. If we consider the first option, then in this case we can not do without a dynamic transceiver. Connections via the expander, as a rule, significantly increase the level of logical zero.
The scheme with 13 transceivers
Interface converter RS-232/485 for 13The transceivers are connected through an overlay. On average, the current consumption parameter in the devices is 120 mA. Trimming resistors are used to reduce the risk of interference. Thyristors are usually installed in a commutated type.
Directly the lining is used withamplifier. For half-duplex data transfer such converters are suitable. On average, the output resistance of these devices does not exceed 4.5 ohms. The sensitivity of the cascade in this case is no more than 170 mV.
Converters 50 mA
RS-485 (interface-converter) for 50 mAsuitable only for automated systems. A distinctive feature of the models is the high data transfer rate. Direct connection of modifications is carried out through galvanic isolation. In this case, the sensitivity of the cascade does not exceed 150 mV. The logical zero level is 230 mV. If we consider devices for bi-directional data exchange, then their expander is of the impulse type. In turn, the transceiver is suitable only for dynamic.
Converters 120 mA
RS-485 (interface-converter) for 120 mAconnected via duplex transistors. If we consider modifications with an indication system, then they use a dynamic transceiver. For a half-duplex exchange, these devices work well. In total, it is possible to connect no more than ten transceivers. As a rule, the level of a logical unit does not exceed 130 mV.
In this case, the number of drivers depends on thepower of the main amplifier. The expander is mainly of the impulse type. The maximum length of one segment is 1300 ns. For automation systems, the devices work well. The rate of signal growth, as a rule, does not exceed 1.1 V per microsecond.
Half-duplex devices
RS-485 (interface converter)half-duplex type is able to connect through a code transistor. For this purpose, the thyristor is used with a main amplifier. The transceiver is used both as a dynamic and field type. The output resistance in the circuit does not exceed 5.4 ohms. The average current consumption is 130 mA. The data reception indication in this case is standard.
The file transfer rate does not exceed 100 bits ingive me a sec. The sensitivity of the cascade is at the level of 230 mV. It is also important to note that the connection of the transducer can be carried out through a truncated expander. In this case, the resistor is of the adjustable type. Directly the thyristor is used with a switched amplifier. There are three capacitors in the circuit.
Differential Modifications
Differential RS-485(interface-converter) are used exclusively for modem cables. The data reception indication in this case is provided. The power supply of the converters is via the Yusb-port. Many models support "Windows 7" and XP. The current consumption is equal to 190 mA. The logical unit level is not more than 90 mV.
To connect the equipment is not usedonly capacitors, but also field resistors. The logical zero level, as a rule, does not exceed 120 mV. The speed of signal generation in this type of model is very high. The sensitivity index of the converter-interface RS-485 (RS-232) has a level of 170 mV. The rate of signal growth does not exceed 1.2 V per microsecond.
Connection via the operative expander
If we consider the connection scheme throughoperational amplifier, it is important to note that the current consumption parameter should not exceed 200 mA. At the beginning of the circuit is the terminal box. The thyristor is used only for a couple of capacitors. In total, the system provides two plates. The transistor is suitable only for the code type. In this case, the logical unit level does not exceed 150 mV. Buffer amplifiers for such circuits are not suitable. In total, it is allowed to connect to the transducers no more than six transceivers.
Converter and single-ended expander
Interface converter RS-485 with single-cycleexpanders need for modem cables. The system of indication of data reception for models is provided by a diode type. On average, the current consumption does not exceed 230 mA. Only devices for half-duplex data exchange are suitable. The transmission speed of the information does not exceed 120 bits per second.
It is also important to note that models usehigh current protection system. Directly powered device is from the Yusb-port. The average sensitivity of the cascade is 160 mV. The speed of signal generation in the models is quite high. The transceiver in galvanic interchanges, as a rule, is used dynamic type. The cover is mainly used with a buffer amplifier. Splitter interface RS-485 output impedance has no more than 5.8 Ohm.
Application of open resistors
Devices with open resistors are producedat 120 and 200 mA. Direct connection is via the terminal box. The power supply of the models is through the Yusb-port. The rs 485 interface converter is suitable for half-duplex communication. Trunk amplifiers are very rare in systems of this type. Expanders are most often used by impulse type. On average, the level of the logical unit is no more than 135 mV. The maximum length of one segment fluctuates around 1300 nm.
Using a Wave Transceiver
Modifications with wave transceivers are suitable ashalf-duplex, and bi-directional data exchange. The data transfer rate in this case is about 230 bits per second. In total, the device is capable of supporting about ten transceivers. On average, the length of one segment does not exceed 1400 nm. In turn, the output resistance is 5.1 ohms. The rate of increase in the signal in this case depends on the type of amplifier.
