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Figure 2: An example of a switch interconnection diagram
PHY forms the physical interface and is responsible for coding and decoding the data between the transmission medium and the digital system.
Linking 10BASE-T1L to machines 10BASE-T1L is designed to replace the 4-20mA standardised signal in many, if not most, process automation applications. However, this does not mean that older fi eld instruments connected via 4-20mA current loops will have to be replaced with 10BASE-T1L-capable fi eld instruments. These conventional devices can be connected via software-confi gurable I/O (SWIO) modules, while remote I/Os serve as a collection point for connection to the PLC with a 10Mbps Ethernet uplink. Software-confi gurable I/O modules
have reconfi gurable module channels, which allows them to work quickly, easily and remotely, without requiring extensive
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rewiring. The channels can be confi gured either as input or output, both for currents and voltages, or digital and analogue signals.
In some cases, there is a requirement that both power for the devices and their data be provided via 10BASE-T1L, which is defi ned as part of the standard. Figure 1 shows an example of a mix of conventional fi eld instruments connected via a 4-20mA current loop and new 10BASE-T1L-capable fi eld instruments. 10BASE-T1L supports two amplitude modes: 2.4V for cable lengths to 1000m and 1V for shorter distances, to 200m. Through the 1.0V peak-to-peak amplitude mode, this technology can also be used in explosion-protected environments (hazardous areas) and meets the strict maximum energy consumption requirements applicable there. An industry consortium has specifi ed
the advanced physical layer (APL), which builds on the 10BASE-T1L standard, defi ning intrinsically safe operation for process automation. Ethernet-APL likewise enables the transition to seamless process automation installations with fi eld-to- cloud connections, including areas with potentially explosive atmospheres for installations in the food and beverage, pharmaceutical, and oil and gas industries. Furthermore, APL also defi nes the power provisioning classes over the single twisted pair lines. No concrete transmission medium (cable) is defi ned with 10BASE-T1L. Only the requirements for return and insertion losses of the cables are specifi ed. Fieldbus Type A cables are the cables of choice. This allows the reuse of existing PROFIBUS or Foundation Fieldbus cabling. 10BASE-T1L works with a balanced pair of conductors over a cable length to 1000m without any problems. However, in noisy industrial environments, a shielded cable like Type A cable is required – using connectors, screw terminals, or punch-down blocks. Some 10BASE-T1L switch chips have integrated diagnostics functions that check the signal quality over the cables. 10BASE- T1L is thus a very robust communication technology – even a mix-up of the wires does not pose a problem.
10BASE-T1L advantages Conventional 4-20mA with HART and fi eldbus devices have a limited data bandwidth of just a few kbps. With 10BASE-T1L, speeds of 10Mbps can be reached. This makes it possible to transmit not only a process value but also additional device parameters such as confi guration and parameterisation information. In the future, possible software updates for the increasingly- complex sensors, as well as fault and network diagnostics, such as short circuits on the line to the sensor, will be performed relatively quickly via the data line. Confi guration is also easier because gateways and converters are no longer
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