Endress+Hauser iTEMP TMT85, Руководство по эксплуатации

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System integration iTEMP TMT85
28 Hauser
• All fieldbus devices are powered via the H1 bus. Like the fieldbus devices, the power
supply unit is connected in parallel to the bus line. Devices requiring external power
must use a separate power supply.
• The line structure is one of the most common network structures. Star, tree or mixed
network structures are also possible using connecting components (junction boxes).
• The bus connection to the individual fieldbus devices is achieved by means of a T-
connector or via a spur. This has the advantage that individual fieldbus devices can be
connected or disconnected without interrupting the bus or the bus communication.
• The number of connected fieldbus devices depends on various factors, such as use in
hazardous areas, the length of the spur, cable types, current consumption of the field
devices, etc. (→  16).
• When fieldbus devices are used in a hazardous area, the H1 bus must be equipped with
an intrinsically safe barrier before the transition to the hazardous area.
• A bus terminator is required at each end of the bus segment.
High Speed Ethernet (HSE):
The superior bus system is realized via the High Speed Ethernet (HSE) with a transmission
rate of max. 100 MBit/s. This serves as the 'backbone' (basic network) between various
local sub-networks and/or where there is a large number of network users.
7.1.2 Link Active Scheduler (LAS)
The FOUNDATION Fieldbus TM works according to the 'producer-consumer' relationship.
This offers many advantages.
Data can be directly exchanged between field devices, e.g. a sensor and an actuating valve.
Each bus user “publishes” its data on the bus and all the bus users configured accordingly
obtain these data. The publication of these data is controlled by a “bus administrator”,
known as the “Link Active Scheduler”, which centrally controls the time sequence of the
bus communication process. The LAS organizes all the bus activities and sends
corresponding commands to the individual field devices.
Other tasks of the LAS include:
• Recognizing and reporting newly connected devices.
• Logging out devices that are no longer communicating with the fieldbus.
• Maintaining the “Live List”. This list contains a record of all the fieldbus users and is
checked regularly by the LAS. If devices are logged on or logged off, the "Live List" is
updated and sent immediately to all the devices.
• Requesting process data from the field devices according to a fixed schedule.
• Allocating send rights (tokens) to devices between unscheduled data transfer.
The LAS can run redundantly, i.e. it exists both in the process control system and in the
field device. If one LAS fails, the other LAS can accurately take over communication.
Thanks to the precise timing of bus communication via the LAS, the FF can run exact
processes at regular, equidistant intervals.
Fieldbus devices, such as this head transmitter, which can take over the LAS function
if the primary master fails, are called “Link Masters”. This contrasts with simple "Basic
Devices", which can only receive signals and send them to the central control system.
The LAS functionality is deactivated in this head transmitter when the unit is
delivered.
7.1.3 Data transfer
A distinction is made between two types of data transfer:
•
Scheduled data transfer (cyclic): All time-critical data, i.e. continuous measurement or
actuating signals, are transmitted and processed according to a fixed schedule.
• Unscheduled data transfer (acyclic): Device parameters and diagnostic information
that are not time-critical for the process are only transmitted over the fieldbus when
required. Data transmission only takes place in the intervals between cyclic (scheduled)
communication.