Fibre optic converters in industrial Ethernet networks
The development of advanced automation systems processing large volumes of data and the need to provide an effective, easy data exchange between the devices is the reason Ethernet is now commonly used in the industry. In most applications, devices providing communication through copper cables are used. Cat. 6a UPT cables are easy to connect, cheap and provide relatively good throughput. It can also supply energy to remote devices including cameras, Wi-Fi access points via a single cable using POE standard.
In the LAN framework, the solutions can be based on different media (optical fibres and copper) including:
10GBase-T - copper systems transmitting at a rate of 10 Gbit/s over unshielded Cat. 6a or 7 UTP over distances up to 100 m. Cat. 6 UTP may reach a distance of up to 55 m;
10GBase-SR - optical transport systems using multi-mode fibre with a reach of up to 82 m (850 nm wavelength). It allows distances up to 300 metres over multi-mode 2000 MHz/km fibres;
10GBase-LX4 - optical transport system using Dense Wavelength Division Multiplexing (DWDM) technology at a distance of 240-300 m over multi-mode fibre (1310 nm wavelength) or up to 10 km over single-mode fibre;
10GBase-LR - Ethernet transmission over single-mode fibre over distances up to 10 km;
10GBase-ER - Ethernet transmission with a reach of up to 40 kilometres over single-mode fibre;
10GBase-SW, 10GBase-LW and 10GBase-EW - solutions equivalent to 10GBase-SR,
10GBase-LR and 10GBASE-ER using synchronous transmission over the same fibre types and at a similar range.
Despite many advantages, using UTP in some applications is less than optimal. Due to parasitic resistances and capacitances, the distance is limited to approx. 100 m. It is theoretically possible to use the signal amplifiers every 100 m, however, it is costly and inconvenient. With an increase in cable length, a risk of electromagnetic interferences generated by high-power devices also increases. In this case, an optical fibre link offering a wider bandwidth, higher transmission distances and EMI immunity may be considered. At distances from 300 m up to tens of kilometres, the optical fibre is a good alternative in industrial applications which require monitoring of remote devices including pumping stations, water tanks, solar panels etc. The applications often use switches with an optical fibre port, however, a media converter may be considered for the next retrofitting or expansion of an existing infrastructure. The following parameters should be considered when selecting the converter:
- Data transfer rate. Standard PLC controller requires relatively low data transfer rates up to 100 Mb, however, 4K IP cameras generate large data volumes and require high data transfer rates up to 1 Gb.
- Transmission distance depends on fibre type: single-mode or multi-mode, and wavelength. The transmitters operating at higher wavelengths provide communication over longer distances. For example, at 850 nm, the transceiver provides transmission over up to 550 m, and at 1310 nm, the distance reaches up to 40 km.
- Power input - standard media converter up to 1 Gbs usually requires 3-5 W.
- Power supply of network devices. If the network devices require power supply, PoE technology might be considered.
Antaira Technologies offers a series of managed and unmanaged media converters with the following features:
- compact and easy to install in the existing control cabinets,
- 10/100Tx to 100Fx transmitters with optional SC / ST connection and multi-mode or single-mode fibre,
- optional passive PoE power supply compliant with IEEE 802.3af,
- 10/100 / 1000Tx / 1000SX / LX SFP for Gigabit fibre,
- built-in LLF (Link Loss Forwarding) and LFP (Link Fault Pass-Through),
- CE, FCC and UL Class 1 Division 2 certificates,
- wide operating temperature range -40 to 80°C.
We can now discuss the converter features advanced self-test functions providing stable operation. Advanced Antaira Technologies converters feature LFP (Link Fault Pass-through) and FEF (Far End Fault) functions. Let’s consider what would happen if the copper cable connecting the switch on the left with the optical fibre converter was unexpectedly disconnected (Fig. 1). In this case, the switch on the right would not receive any information about the interrupted transmission and the network would operate without reporting an error on the assumption that the connection is still available. The fault can be detected by the LFP function. Another key function is the FEF (Far End Fault). Let’s consider what would happen if the optical fibre connecting the media converter was unexpectedly disconnected (Fig. 2).
In this case, data transmission through the optical fibre would not be possible. The switch on the left would not be able to transmit data to the switch on the right. However, if the other fibre was connected, the switch on the right would continue transmission to the switch on the left, which may lead to transmission errors i.e. a far end fault. The functions will only work correctly with a pair of converters. For a converter connected to a network switch, LFP and FEF functions will not work correctly and the network will not be able to use its self-test function. The converters should not only be used in pairs but should be of the same brand and model, since different device suppliers may use proprietary protocols for those functions.
A series of standards regarding cybersecurity are available, including NIST 800-53, NERC CIP for power industry or IEC 62443. The standards include guidelines for system designers, network device manufacturers and users by defining good practices for secure industrial automation systems. IEC 62243 lists the potential problems that must be addressed when designing network devices to ensure security, including
The biggest advantages of using industrial Ethernet media converters is easy implementation and low cost. The fibre optic technology offers high data transfer rates and electromagnetic interference and overvoltage immunity. LFP and FEF provide self-test and connection fault detection function. All those features makes the converter very popular in industrial automation applications.