Can Ethernet Gateway

Intrinsic Safe Ethernet equipment for hazardous areas from MTL Instruments

Different methods are used in process automation to power and communicate with end devices, including 4-20mA, a variety of different Fieldbus standards, serial communications such as RS232, RS422 and RS485 as well as video, telephony and Ethernet.  

Ethernet is the ideal solution where applications require high bandwidth as it provides open connectivity and can be combined with Ethernet Remote I/O and Linking Devices to connect to low bandwidth 4-20mA and Fieldbus systems.  

Use of Ethernet in hazardous areas is very rare because of the high cost of installation and the limitations involved in carrying out maintenance.  

The 9460-ET Series from MTL Instruments provide cost-effective Intrinsically Safe (IS) Ethernet equipment for installation in hazardous areas with easy maintenance.    

The intrinsically safe hazardous area certification permits the components to be mounted in a Zone 1, or Division 1 hazardous area with connectivity into Zone 0 and the associated apparatus certification of the 9468-ET IS Ethernet isolator and 9491-PS IS power supply allow this equipment to be mounted in a Zone 2 hazardous area and connected to intrinsically safe equipment in a Zone 0 or 1, or Division 1 hazardous area.  

The 9460-ET Series of IS Ethernet equipment consists of IS Copper to Fibre Converter, IS Ethernet Switch, IS Ethernet Isolator, IS Serial – Ethernet Gateway and IS Wireless AP/Bridge with all components being certified IECEx.

Ethernet Gateway Extends the Reach of CAN Applications | esd ...

One of the ingenious features of CAN, the bit monitoring, contributes not only to the enormous reliability of Controller Area Network, but it is ironically also responsible for its biggest drawback, the limited physical distance of the CAN bus. Restricted physical distance is definitely an issue especially for applications such as elevators, security systems and other building technologies. The one and only way to extend the usable bus length without compromising the reliability is to lower the baud rate. In cases where baud rate is not the main focus, e.g. diagnostics and low priority messaging, a CAN bus can be extended as far as the reach of the Internet.

While a distance of roughly 150 ft. at 1 Mbit/sec seems to be restrictive, especially for building technologies, a baud rate of 1 Mbit/sec can nevertheless be considered an overkill for such applications. Experience has shown that the vast majority of automation applications can work sufficiently with baud rates of 500 kbit/sec or even 250 kbit/sec and that includes demanding motion control applications.

The bus length extension per CAN repeaters is a myth that is unfortunately being maintained by some manufacturers and vendors of these devices. CAN repeaters provide primarily electrical isolation and signal conditioning.

While CAN can be operated with a simple twisted pair of wires, the quality of the CAN bus cable can be a major factor in terms of maximum bus length. Poor cable quality will quickly knock a signal strength down below a receiver’s threshold. The result will be signal errors and consequently increased bus traffic due to error frames and repeated messages.

CAN repeaters can be used to boost the signal strength and maintain standard bus lengths, but not extend them. The only extension is the one from a poor quality network to a properly functioning network. Ironically, CAN repeaters, due to their internal delay times in the range of milliseconds, will actually shorten the usable bus length in the range of several meters.

Some vendors in the CAN business offer a variety of interfaces that support the communication between two separate CAN networks (e.g. the CAN-CBM-Bridge by esd electronics, Inc. See: http:// www.esd-electronics-usa.com). Such devices allow to extend a CAN network by a factor of two, but they, too, have latency times due to reception, processing and re-transmission of CAN frames. Another disadvantage is that, for instance, both CAN networks cannot exchange error frames.

Architecture of Computing Systems Arcs 2011, 24th International Conference, Lake Como, Italy, February 24-25, 2011

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