The basic IS application uses a redundant pair of H1 with Integrated Power cards to provide power to field devices connected through one or more IS Field Barriers. The available power to a field device depends on the length and resistance characteristics of the fieldbus cable to each Field Barrier and the output characteristics of the Field Barrier to the field device. The loads listed in the table in the topic Maximum distances per load with Field Barriers are the normal loads required by the barriers and devices. However, the numbers take into account the additional current required if a load on one barrier is accidentally shorted (during a maintenance operation) to protect the segment from being affected.
The P+F segment calculator tool was used to make the example calculations in the table in the topic Maximum distances per load with Field Barriers. The calculations show the maximum distance for a given load on the Fieldbus Power Hub for applications using 2, 3, and 4 Field Barriers to connect up to 16 field devices. Remember the redundant H1 card requires 24 mA of fieldbus power. The calculations are based on the following assumptions:
There will be different restrictions and limitations on your segment if these assumptions do not hold for your segment layout. If your devices average more than 20 mA per device, reduce the maximum cable length indicated in the table for that number of devices or reduce the number of devices on the segment. Refer to the device documentation for information on current requirements for the device. If these assumptions do not properly represent your specific application, it is recommended that a calculation be completed to verify that the segment design adequately meets your process requirements.