Maintenance in Modern Remote I/O and Fieldbus Installations

Modern process instrumentation makes use of digital data transmission to interface the plant level of sensors and actuators with the process control system. These relatively new technologies often raise concerns with plant maintenance engineers who may be more familiar with conventional 20 mA signals. However, these concerns are not warranted!

Remote I/O in particular has a decade of field experience offering simple means to help with everyday maintenance issues. As an example, conventional multimeters can be used for many tasks - even down to a check of the bus line. It is even possible to detect multiple bus terminations as well as non-terminated bus lines while measuring from the control room. This also applies to hazardous area applications with PROFIBUS or Modbus using increased safety RS485 busses.

PROFIBUS PA and FOUNDATION fieldbus can be diagnosed with modern PC based, user-friendly analyzers referencing the physical layer. These can be installed on a permanent basis to monitor for aging connections which might degrade signal quality.

Remote I/O offers additional benefits for conventional field devices. HART field equipment can be addressed from a central position making use of the HART-via-PROFIBUS standard. Handheld communicators are no longer required. Remote I/O receives HART data from the operator station via PROFIBUS. This digital communication is superimposed on the 20 mA current loop of all connected transmitter supplies and output isolators. Field devices can also be addressed via PROFIBUS using their device specific parameters.

Remote I/O makes use of a combination of explosion protection techniques such as intrinsic safety for I/O channels, increased safety for power connections, and flame proofing for power supplies. These techniques ensure that live maintenance is possible even to the extent that flame proof modules can be hot swapped under hazardous conditions in Zone 1 without the need for a hot work permit.

There are also Zone 1 replaceable fuses to protect high power valves or other equipment. Pepperl+Fuchs offers our expertise in systems and solutions to ensure that Zone 1 or Zone 21 mounted cabinets are as safe as those for Zone 2 and 22 or the safe area. This includes temperature proofing for all hazardous location installations.

Maintenance personnel can build on their experience to service Remote I/O and fieldbus installations at their plant. By employing established tools like multimeters and laptops, maintenance crews can analyze a bus and ensure quick and efficient service operations.