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This robustness is the main reason why RS-485 is well suited for long-distance networking in noisy environment. It is better to educate oneself on RS485 and Ethernet because you would be facing customers in the networking field and very familiar with these terms. We use 2 pair telephone cable for RS485 communication up to 1200 metres. As a rule of thumb, the speed in bit/s multiplied by the length in metres should not exceed 108. Thus a 50-meter cable should not signal faster than 2 Mbit/s. Under some conditions it can be used up to data transmission speeds of 64 Mbit/s. In a computer system, SCSI-2 and SCSI-3 may use this specification to implement the physical layer for data transmission between a controller and a disk drive. RS-485 signals are used in a wide range of computer and automation systems. These characteristics make RS-485 useful in industrial control systems and similar applications. These characteristics include: definition of a unit load, voltage ranges, open-circuit voltages, thresholds, and transient tolerance. RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems. In contrast to RS-422, which has a driver circuit which cannot be switched off, RS-485 drivers use three-state logic allowing individual transmitters to be deactivated.

RS-485 standard conformant drivers provide a differential output of a minimum 1.5 V across a 54-Ω load, whereas standard conformant receivers detect a differential input down to 200 mV. The foreword to the standard references The Telecommunications Systems Bulletin TSB-89 which contains application guidelines, including data signaling rate vs. In theatre and performance venues, RS-485 networks are used to control lighting and other systems using the DMX512 protocol. The WattNode® BACnet and Modbus® meters communicate using RS-485 (TIA/EIA-485-A) half-duplex, differential signaling at 9600, 19200, 38400, and 76,800 baud. The EIA has officially disbanded and the standard is now maintained by the TIA as TIA-485, but engineers and applications guides continue to use the RS-485 designation. The EIA once labeled all its standards with the prefix "RS" (Recommended Standard), but the EIA-TIA officially replaced "RS" with "EIA/TIA" to help identify the origin of its standards. It does not specify or recommend any communications protocol; Other standards define the protocols for communication over an RS-485 link. The most common cable type is Cat 5e-UTP (unshielded twisted pair) which may work over shorter distances in less demanding applications with low EMI noise levels. Can i use Cat 5e-UTP instead of Shielded cables?

Category 5 (Cat 5, Cat 5e, and Cat 6) cables are the most common Ethernet cables in use today. This way, the lines will be biased to known voltages and nodes will not interpret the noise from undriven lines as actual data; without biasing resistors, the data lines float in such a way that electrical noise sensitivity is greatest when all device stations are silent or unpowered. The shield works as a "drain" for any noise that could be picked up by the RS485 network and "drain" it to ground. It gets away most of the time with this configuration, with the shield draining noise and providing the ground reference at the same time. GND connection. You still need to pay attention to the shield connection in either case. You need a third ground wire to make sure that no one on the network violates the common mode voltage specification. Also, when some devices on the RS485 are NOT opto-isolated, the third wire becomes essential to avoid the units being damaged. LAPP manufactures a range of Unitronic Serial RS485 Cable range. A CAT6 cable can theoretically carry data for 100m but after 80m, there would be signal attenuation and it would be impractical.

An RS485 cable can carry data upto 4000ft (or 1.2km) @ 100kbps as shown below. It is important to know how to wire devices on an RS485 network, especially when a non opto-isolated device is present. Be sure to use a wire pair such as the blue and blue/white pair for the data lines and a third wire or pair twisted together for the common connection. And you should never use the shield as a third conductor. No matter the devices, it is always good on real site installation to use a shielded cable, with 18-22AWG wiring and the shield connected ONLY to one end of the line. End of line termination resistor (120 ohm 1/4 watt) to be installed at both ends of network. And the results before was a degraded signal that the devices near the end would interpret the signal incorrectly. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. RS-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. This cable is supplied in a 200 metre length on a timber drum and provides a one cable run solution to each access controlled door.