Properties of the FOUNDATION Fieldbus H1

Like PROFIBUS PA, the FOUNDATION Fieldbus H1 is also based on IEC standard 61158-2. With MBP (Manchester coded Bus Powered) transmission technology, digital data is transmitted and power is supplied to the bus nodes on a shielded two-wire cable. The constant transmission rate is 31.25 Kbps.

Up to 32 bus nodes (1 coupler + field devices) can be operated on one fieldbus segment (typically 8 to 12 devices). The field devices are integrated into the fieldbus segment via active field distributors AFD4 and AFD8 (approval for Ex zone 2/22) as well as via AFDiS (approval for Ex zone 1/21). Intrinsically-safe FF devices connected via AFDiS active field distributors can be installed in hazardous areas in accordance with Ex zone 1/21 or 0/20.

The total length of the fieldbus segment is restricted to 1 900 m. If AFD4/AFD8 are used, the length of the spur lines for connecting devices and the quality of the cable used must also be considered when calculating the total length of the bus segment. Spur lines on the AFDiS are not relevant to the total length of the bus segment.

The spur lines can have the following maximum lengths:

• Up to 120 m in accordance with IEC 61158?2
• Up to 60 m in accordance with IEC 60079?27 (FISCO)

With AFD4/AFD8 active field distributors, the maximum values may be reduced depending on the number of spur lines of the bus segment (for details, see section "Technical specification"). With the active field distributor AFDiS, this reduction is canceled by the integrated repeater function.

The SIMATIC Fieldbus Calculator provides help in calculating and designing fieldbus segments:
http://support.automation.siemens.com/WW/view/en/53842953

The FOUNDATION Fieldbus H1 combines cyclic and acyclic communication. Time-critical tasks such as the transfer of process data are executed cyclically according to an exact processing schedule. On the other hand, non-time-critical information such as maintenance/diagnostics data, configuration or configuration data is transferred acyclically.

Device management with EDD

The field device data for the following block types are distributed according to the block model:

• Device block (device-specific information)
• Function block (implemented functions)
• Transmission block (function for controlling input/output variables of a function block)

Fieldbus Foundation provides pre-defined device descriptions (standard DD) for the basic functions of specific field device types. The basic functions of the devices (e.g. analog input, digital output, etc.) are implemented by means of various standard function and transmission blocks.

The device descriptions are interpreted with SIMATIC PDM.

Control in the field

Function and transmission blocks can also be interconnected to form control loops. Together with suitable field devices, such a control application operates independent of the controller (automation system) of the control system.

Characteristic features at a glance

• Bus power supply to the field devices
• Topology: Line, tree, ring
• Integration of intrinsically safe field devices in hazardous areas with barriers
• Deterministic time response
• Interoperability due to standardized bus interface and device integration with standardized device descriptions
• Support of "Control in the field"