Technology Update of Fieldbus

If your fieldbus network had a report card, the most important area for  connectors to get high  marks in would be "Plays Well with Others." The connector plays a key role in the ability of each device to "talk" on the network. The fundamental philosophy of open bus networks is to have each device interconnect and communicate with all the other devices, regardless of manufacturer. As such, the vendor associations or foundations of open buses provide specifications to device, connector and cable vendors to designate connector types, wire colors and pin outs. This ensures that a device added to the network today or in the future will connect to the network without making any existing connection obsolete.


Some of the leading open buses are DeviceNet, Profibus DP, Foundation Fieldbus, AS- Interface, Interbus-S, SDS, Seriplex and CANbus. These systems have been standardized on all or a combination of these industrial connectors:

* mini - a sealed connector (IP67, NEMA 6P) based on a 0.875 --7/8-16-- in. barrel; connectors are rated for 600 V, 9.0 A and available with two to seven contacts.

* micro - a sealed connector (IP67, NEMA 6P) based on a 12 mm barrel. Connectors are rated for 300 V, 4.0 A and are available with two to six contacts.

* 9DB - a subminiature, nine-pin, D-shell connector.

* open - a nonsealed, pluggable connector in which the conductors are inserted into a screw- terminal or spring-loaded contact.


The sealed connectors are suitable for the harsh environments found on most factory floors. These types of connectors are capable of keeping out damaging fluids and providing strain relief when the cable is subjected to mechanical stress. The 9DB and open connectors are not suitable for harsh environments; they are used primarily for connections to either a bus coupler or a PLC.


The cabling system of a network consists primarily of a data trunk cable, data drop cables, tees and terminators. The trunk cable is the main busline that carries the network messages. The data drop cables are connected with a tee coming off of the main busline, and they carry the data to and from the addressable devices, known as nodes. The terminator resistor is connected to the beginning and end of a network, in lieu of another extension of the main bus line, to stabilize and tune the signal. Because all of the data is carried through the main trunk line, poor connections have a cumulative effect on the system. 


With the cost of troubleshooting and downtime in today's manufacturing plants, the concept of the connectors "playing well with others" is extremely important. All components must plug-and-play seamlessly without creating network problems.


This article is written and provided by Ann Feitel of InterlinkBT. InterlinkBT supplies bus components for all of the major open buses. They recommend and supply the best bus protocol and hardware topology to meet your specific needs. For more information about InterlinkBT or their products please visit their website at: