RS-485 is a type of converter that is used in industrial networks. It is also used in differential lines. Most often there are modifications for USB-connectors. The principle of operation of the element is based on the transmission of data by sending low-frequency pulses.
Converters differ among themselves primarily in the output resistance parameter. It should also be borne in mind that models are produced with different data rates. In order to understand them in more detail, it is necessary to consider the connection scheme of the modification.
Standard wiring diagram for the converter
The usual converter connection scheme includes self-regulating resistors, as well as an expander. A thyristor is most often used as a switched type. In order to avoid network congestion, linings are applied. In some cases, electromagnetic type kenotrons are installed to transmit the signal. In total, the circuit can have up to five capacitors. On average, the output impedance does not exceed 5.5 ohms. If we consider the industrial RS-485 interface with galvanic isolation, then a pulse expander is used there.
100 bps model
This type of RS-232/485 interface converter is connected exclusively through a transceiver. In this case, the maximum length of one segment does not exceed 1200 nm. On average, the current consumption parameter is 130 mA. If we consider the converter of Ethernet interfaces RS-485 without expanders, then it uses a buffer amplifier.
Designed to connect a maximum of five transceivers. In this case, the signal stability depends on the current throughput. The RS-485 interface cable provides a logic zero 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 designed, as a rule, to support no more than five transceivers. Devices are suitable for half-duplex communication. Elements are connected most often through the main amplifier. In total, the circuit uses no more than three capacitors. On average, the slew rate of the converters does not exceed 1 V per μs. Expanders are used only pulse type. If we consider 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 on average 150 mV.
600 bits per second models
An RS-485 USB interface converter of this type is used for modem cables. The maximum segment length in this case is 1300 nm. Devices are well suited for bidirectional data transfer. On average, the cascade sensitivity of the converters does not exceed 210 mV. The slew rate is about 1.2 V per μs.
The modification can be connected through a buffer amplifier or a resistor. If we consider the first option, then in this situation you can not do without a wire thyristor. It is also important to note that the capacitor is suitable only with a lining. If we consider the converter-interface RS-485 USB with resistors, then it uses an electromagnetic type kenotron. In this case, the output impedance of the system fluctuates around 4.6 ohms.
10 transceiver models
Converters for 10 transceivers have a high output impedance parameter. This type of device is most suitable for bidirectional data transmission. The current consumption parameter is on average 230 mA. The data transfer rate does not exceed 130 bits per second. Models are ideal for automated systems.
The slew rate of the converters does not exceed 1.3 V per μs. The sensitivity of the cascade in this case is negligible. Directly connecting devices through adjustable resistors or an expander. If we consider the first option, then in this case we can not do without a dynamic transceiver. Connections through an expander, as a rule, significantly increase the level of logical zero.
13 transceiver circuit
The RS-232/485 interface converter for 13 transceivers is connected via a plate. On average, the current consumption in devices is 120 mA. Trimmer resistors are used to reduce the risk of interference . Thyristors are usually installed in a switched type.
Directly lining is used with an amplifier. For half-duplex data transmission, such converters are well suited. On average, their output impedance does not exceed 4.5 ohms. The sensitivity of the cascade in this case is not more than 170 mV.
50 mA converters
50 mA RS-485 (converter interface) is only suitable for automated systems. A distinctive feature of the models is a high data transfer rate. Modifications are directly connected via galvanic isolation. In this case, the cascade sensitivity does not exceed 150 mV. The logical zero level is 230 mV. If we consider devices for bi-directional data exchange, then they have an expander using a pulse type. In turn, the transceiver is suitable only dynamic.
120 mA Converters
RS-485 (interface converter) 120 mA is connected via duplex transistors. If we consider modifications with an indication system, then they use a dynamic transceiver. For half-duplex communication, these devices are well suited. 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 the power of the main amplifier. The expander is mainly used in pulse type. The maximum length of one segment is 1300 ns. For automation systems, devices fit well. The slew rate, as a rule, does not exceed 1.1 V per μs.
Half duplex devices
The half-duplex RS-485 (interface converter) is capable of connecting via a code transistor. For this, the thyristor is used with a main amplifier. The transceiver is used both dynamic and field type. The output impedance in the circuit does not exceed 5.4 ohms. The average current consumption is 130 mA. Indication of data reception in this case is standard.
File transfer speed does not exceed 100 bits per second. The cascade sensitivity is at 230 mV. It is also important to note that the connection of the converter can be done through a spanning expander. In this case, the resistor is suitable for an adjustable type. The thyristor is directly used with a switched amplifier. In total, the circuit has three capacitors.
Differential modifications
Differential RS-485 (converter interface) are used exclusively for modem cables. Indication of data reception in this case is provided. Converters are powered via USB port. Many models support Windows 7 and XP. The current consumption indicator is not more than 190 mA. The level of the logical unit is not more than 90 mV.
To connect the equipment, not only capacitors are used, but also field resistors. The level of logical zero, as a rule, does not exceed 120 mV. The signal generation rate for models of this type is very high. The sensitivity index of the cascade converter-interface RS-485 (RS-232) is at the level of 170 mV. The slew rate does not exceed 1.2 V per μs.
Connection via online expander
If we consider the connection scheme through an operational amplifier, it is important to note that the current consumption parameter should be no more than 200 mA. At the beginning of the circuit is a terminal box. The thyristor is only used in conjunction with capacitors. In total, the system has two covers. The transistor is suitable only for code type. In this case, the level of the logical unit does not exceed 150 mV. Buffer amplifiers are not suitable for such circuits. In total, no more than six transceivers can be connected to the converters.
Converter and single stroke expander
An RS-485 interface converter with single-ended extenders is needed for modem cables. The data reception indication system for the models is provided for a diode type. On average, current consumption does not exceed 230 mA. Only half-duplex communication devices are suitable. The speed of information transfer they do not exceed 120 bits per second.
It is also important to note that the models use an overcurrent protection system. The device is directly powered by the USB port. The cascade sensitivity index averages 160 mV. The signal generation rate of the models is quite high. A transceiver in galvanic isolation is typically used of a dynamic type. The cover is mainly used with a buffer amplifier. The RS-485 interface splitter has an output impedance of no more than 5.8 ohms.
Open resistors
Devices with open resistors are produced at 120 and 200 mA. Direct connection is via a terminal box. Power supply of models is made through usb port. The rs 485 interface converter is suitable for half duplex communication. Trunk amplifiers are very rare in this type of system. Expanders are most often used pulse type. On average, the level of the logical unit is not more than 135 mV. The maximum length of one segment fluctuates around 1300 nm.
Using a wave transceiver
Modifications with wave transceivers are suitable for both half-duplex and bidirectional 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 impedance is 5.1 ohms. The slew rate in this case depends on the type of amplifier.