This article is about terminators used in FF Segment, number of fieldbus devices connected per segment of fieldbus devices, current consumption in fieldbus devices, Foundation fieldbus segment.
Number of Fieldbus Devices Connected per Segment of Fieldbus
The following explains how the number of Fieldbus devices connected to one segment should be determined.
How many terminators are used per segment in FF?
Up to 32 Fieldbus devices can be connected to one H1 segment based on the FOUNDATION fieldbus standard. Because the host interface is included among these Fieldbus devices, a Fieldbus communication module ALF111 is also counted as one device.
Therefore, up to 31 Fieldbus devices can be connected for the single ALF111 configuration, and up to 30 Fieldbus devices can be connected for the duplexed ALF111 configuration.
Taking the Current Consumption into Consideration When Determining the Number of Connected Units
The number of Fieldbus devices that can be connected to one segment should be determined in such a way that the total current consumption of the Fieldbus devices does not exceed the supplied current capacity of the power supply unit.
If it has not been determined which Fieldbus devices should be used, tentatively set the current consumption per Fieldbus device to be 20 mA on average (the rated current consumption of Yokogawa Electric-made EJX devices is 15 mA, and 17 mA for YVP devices), and decide the number of Fieldbus devices connected to one segment so that the total current consumption of Fieldbus devices does not exceed the supplied current capacity of the power supply unit.
The table below lists the supplied current capacity of typical power supply units.
Supplied Current Capacity of Power Supply Units
Note: If a Fieldbus device has a built-in power supply (battery), it is excluded from the calculation of power supply capacity. The current
oscillates by approximately 10 mA when a Fieldbus device sends data; therefore, allow margin for that (multiple Fieldbus devices
do not send data at the same time).
Number of Units Connected with Consideration of the Macro Cycle and the Communication Schedule
It is necessary to determine the number of Fieldbus devices, the number of fieldbus blocks and the number of communications so that the execution time of the fieldbus block and the communication schedule fit in the macro cycle.
If Fieldbus devices made by Yokogawa are used, allocate approximately 19 msec per communication and a maximum of 100 msec per fieldbus block as a guideline. The execution time of the fieldbus block varies depending on the Fieldbus device and fieldbus block. For more information, contact your device vendor.
Taking the Function Block Capacity of Each Database Type into Consideration When Determining the Number of Connected Units
The function block capacity is determined by the total number of FOUNDATION fieldbus faceplate blocks (hereinafter referred to as FF faceplate blocks) plus regulatory control blocks and calculation blocks, and varies depending on the database type.
The table below lists the function block capacity of each database type.
Number of Regulatory Control/Calculation Blocks for Each Database Type
Following keywords explains above topics.