Endress+Hauser RID14 Anleitung Seite 47

RID14
H1 bus system:
In the field, fieldbus devices are connected only via the slower H1 bus system that is specified
following IEC 61158-2. The H1 bus system allows simultaneous feed to the field devices and
data transfer on the two-wire line.
The following points describe some important characteristics of the H1 bus system:
• All fieldbus devices are powered via the H1 bus. Like the fieldbus devices, the power supply is
connected in parallel to the bus line. Devices requiring external power must use a separate
power supply.
• One of the most common network structures is the line structure. 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, length of spur, cable types, current consumption of field devices etc. (see
Operating Instructions).
• If using fieldbus devices 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 ' b ackbone' (basic network) between various local
sub-networks and/or where there is a large number of network users.
6.3.2 Link Active Scheduler (LAS)
The FOUNDATION Fieldbus™ works according to the ' p roducer-consumer' relationship.
This provides various 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 this
data. Publication of this data is carried out by a 'bus administrator' known as the 'Link Active
Scheduler', which controls the sequence of bus communication centrally. The LAS organizes all
the bus activities and sends appropriate commands to the individual field devices.
Other tasks of the LAS are:
• Recognition and reporting of newly connected devices.
• Reporting the removal of devices no longer communicating with the fieldbus.
• Keeping the 'Live List'. This list, in which all the fieldbus users are recorded, is checked by the
LAS regularly. 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 in accordance with a fixed schedule.
• Allocation of send rights (tokens) to devices between the untimed data transfer.
The LAS can be 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. Through precise
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Operating the field indicator
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