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Industrial comms call for next-gen components

Posted: 01 May 2007 ?? ?Print Version ?Bookmark and Share

Keywords:industrial communication next-gen components? sensors for industrial communication? industrial networking hierarchy?

Industrial communication includes data monitoring and processing, diagnostic and sensing, and visualizing. It also includes various methods of maintaining data integrity against group loop current or common mode noise, with optocouplers as the most commonly used, as they eliminate both problems. Requirements change over the years. Different technologies and communication buses allow users to select according to their specific requirements, such as speed, switching specifications or security. The hierarchy of industrial networking includes: enterprise (Ethernet PCs, servers and gateways), control (high-performance Ethernet, Ethernet and ProfiNet), device (Profibus DP and DeviceNet) and sensor levels (CAN bus and remote I/O).

Smart sensors are increasingly being used in industrial systems, thus changing device-level communication to a more complex information exchange. Due to increased miniaturization, a sensor becomes a small PC with memory and networking capabilities, allowing sophisticated feedback and more accurate information by onboard calibration to compensate nonlinearity, offset or temperature-related errors. These advantages and the new flexibility result in a success story of smart sensors and boost overall industrial communication. More intelligence is also added in the form of programmable logic controllers (PLCs). They are used to control and handle the information flow on the lower network protocol layers, especially on the sensor and device levels.

Fieldbus is another area that shows great promise, as it also benefits from smart sensors. Fieldbus is often used to connect these individual PLCs together. Among the most popular used today are Profibus, DeviceNet, Interbus and CAN bus with regional emphasis.

To achieve signal integrity, optocouplers are often used on interface cardsfrom slow RS-232 or CAN bus to high-speed RS-485 interfaces. To optimize space consumption, multichannel packages are often preferred. Bidirectional communication channels are very helpful in further reducing board space.

The hierarchy of industrial networking includes enterprise, control, device and sensor levels.

Isolator factor
Requirements for isolators are often expressed in speed or Megabaud (MBd). More valuable for designers are switching-related specifications such as propagation delay and pulse-width distortion (PWD). DeviceNet specifies relatively slow data rates125-, 250- and 500kBaudbut requires less then 40ns propagation delay. CAN bus specifies 125Kbps for low speed and 1Mbps for high speed, but no sharp requirement on propagation delay. Profibus transmits in the 12MBd range and specifies a total PWD delay for isolator, transceiver and connection. To meet overall requirements, an isolator typically needs a PWD delay of 6ns or lower to achieve a higher safety margin for longer distances. Emerging technologies such as capacitive and magnetic isolators offer faster speeds of up to 100MBd, but decreases in communication speed are caused by PWD. Established isolators in the market such as optomagnetic or capacitive couplers provide a PWD delay of as low as 2ns, setting the maximum speed in asynchronous data communication. This can effectively be used without additional components to 50MBd, which optocouplers provide today.

New transceiver generations reflect a shift toward lower supply voltages, especially in the control area where noise is not much of a problem. Supply voltage in the range of 3V is becoming standard now. The availability of 3V isolators allows designers to eliminate one supply and save cost.

New generations of optocouplers optimized for communication applications are thus measured by the flexibility of supply voltage and overall board space consumption. Avago Technologies offers multichannel and bidirectional optocouplers and digital optocouplers that operate at 3V and 5V.

In the future, Ethernet-based communication will become more important. ProfiNet is promoted in Europe by Siemens, while EtherCat is another open standard supported by Beckhoff. Both allow data rates of up to 100Mbps. Isolation is done with transformer technology inherited from computing Ethernet.

Optocouplers have not yet found their place and are challenged by new speed requirements. Use of new-generation high-speed optocouplers and optical fiber-based solutions will be possible in the future. Industrial Ethernet and established field buses will co-exist for at least the next 10-15 years. Thus, optocouplers will continue to provide isolation, guarantee signal integrity and play a key role in industrial communication in the coming years.

- Alexander Jaus
European Business Development Manager, Optical Communication Solutions Division
Electronic Components Business Unit
Avago Technologies Ltd




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