Fieldbus communication
Foundation Fieldbus
i
2 Technical Manual Fieldbus communication
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Technical Manual Fieldbus communication 3
Contents
Contents
1Introduction.............................................................................................. 4
1.1 Target group ................................................................................... 4
1.2 General safety statements.............................................................. 4
1.3 Meaning of the warning notes......................................................... 4
2 Basic principles of the Foundation Fieldbus technology .................... 5
2.1 HSE bus.......................................................................................... 6
2.2 Linking devices ............................................................................... 7
2.3 H1 bus basic principles................................................................... 7
2.4 Bus access ..................................................................................... 9
2.5 Device management....................................................................... 14
2.6 Current and voltage on the H1 bus................................................. 15
3 Installation in the H1 segment - field devices in general ..................... 18
3.1 Grounding and shielding................................................................. 18
3.2 Termination..................................................................................... 19
3.3 PD tag and addressing ................................................................... 20
4 Installation in the H1 segment - Polytron 8000 ..................................... 21
4.1 Opening the gas detector ............................................................... 21
4.2 Connecting the gas detector........................................................... 21
4.3 Connecting the fieldbus cable......................................................... 22
4.4 Checking grounding and shielding.................................................. 22
4.5 Applying the termination ................................................................. 23
4.6 Connecting the power supply ......................................................... 23
4.7 Closing the gas detector ................................................................. 24
5 Commissioning - Polytron 8000 ............................................................. 25
5.1 Checking the installation................................................................. 25
5.2 Configuring the gas detector via DTM ............................................ 25
6 Troubleshooting....................................................................................... 28
6.1 Fault analysis.................................................................................. 28
7Annex........................................................................................................ 29
7.1 Overview of registers and parameters of the function blocks ......... 29
7.2 Appendix 1 List of parameters for Polytron 8000............................ 29
4 Technical Manual Fieldbus communication
Introduction
1 Introduction
This document is a supplement to the instructions for use for the following gas
detectors:
–Dräger Polytron 8100
–Dräger Polytron 8300/ Dräger Polytron 8310
–Dräger Polytron 8700/ Dräger Polytron 8720
This document contains additional information on the PROFIBUS-PA interface.
1.1 Target group
This manual is intended for experts who are specialized in PLC programming,
certified electricians, or persons instructed by certified electricians who are also
familiar with the applicable standards.
1.2 General safety statements
Before using this product, carefully read the associated instructions for use. This
document does not replace the instructions for use.
1.3 Meaning of the warning notes
The following alert icons are used in this document to provide and highlight areas of
the associated text that require a greater awareness by the user. A definition of the
meaning of each icon is as follows:
Alert icon Signal word Consequences in case of nonob-
servance
WARNING Indicates a potentially hazardous situation
which, if not avoided, could result in death
or serious injury.
CAUTION Indicates a potentially hazardous situation
which, if not avoided, could result in injury.
It may also be used to alert against unsafe
practices.
NOTICE Indicates a potentially hazardous situation
which, if not avoided, could result in dam-
age to the product or environment.
Technical Manual Fieldbus communication 5
Basic principles of the Foundation Fieldbus technology
2 Basic principles of the Foundation Fieldbus
technology
Foundation Fieldbus (FF) is an internationally standardized digital communication
system. In many areas, it is replacing analog signal transmission using a 4-20-mA
interface, which is costly in terms of time and resources. Digital communication
offers the following benefits over analog data transmission:
–Significantly less wiring is required. Digital signals and supply voltage are
transmitted via one cable.
–It is much easier to commission and to add or remove field devices.
Standardization allows exchanging of field devices across manufacturers.
–Parameterization, diagnostics and maintenance of field devices can be
performed centrally.
–Data transmission is bi-directional and delivers more information, e.g. status and
error messages.
Foundation Fieldbus (FF) uses 2 bus systems. One or more slower buses (H1 bus)
with Manchester Coding (MBP) are connected to a fast bus system (HSE bus) with
Highspeed Ethernet. The field devices are connected in parallel to the H1 bus and
are supplied with energy via the bus line by a feed unit. The transition between H1
and HSE is made by means of bridges or gateways. With FF, individual field
devices can perform automation tasks so that they no longer act as mere actors or
sensors. This enables decentralized process processing, relieving the bus of part of
the load.
6 Technical Manual Fieldbus communication
Basic principles of the Foundation Fieldbus technology
2.1 HSE bus
Highspeed Ethernet (HSE) is based on Ethernet technology and has a data transfer
rate of 100 Mbit/s. Bus access is arbitrary. Devices can access the bus at any time.
This may negatively impact on real time processing, thus limiting suitability for
applications in automation technology. However, if only a limited number of devices
is connected, the high data transfer rate allows real time processing. In order to
avoid high bus loads resulting from a large number of devices, it is possible to set
up multiple HSE buses that are connected with each other by means of switches.
Switches read out the target addresses of the data packets and pass data on to the
appropriate sub-network.
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Technical Manual Fieldbus communication 7
Basic principles of the Foundation Fieldbus technology
2.2 Linking devices
Linking devices connect the fast HSE bus and individual H1 buses. They convert
the different data rates and telegrams. Linking devices can be bridges or gateways.
2.3 H1 bus basic principles
2.3.1 H1 bus overview
The field devices are connected to the H1 bus. They are capable of executing
automation tasks autonomously and of exchanging data directly at defined points in
time. Several mechanisms are in place to ensure that multiple devices cannot
transmit simultaneously.
2.3.2 Cable type
Field devices and fieldbus network are connected by means of twisted pair cables.
It is not permitted to have multiple electric circuits connected to one cable. The
electrical characteristics of the fieldbus cables determine essential properties such
as the number of participants or distances. Cable type B and cable type A can be
used. If cable type B is used, it is possible to connect multiple fieldbuses of the
same type of protection to one cable. The shielded cable type A must be used for
Dräger gas detectors. If cable type B is used, it is possible to connect multiple
fieldbuses of the same type of protection to one cable.
Standard IEC 61158
Data transmission
(physical layer)
Manchester Coding Bus Powered (MBP)
Max. length from seg-
ment coupler
–1900 m: intrinsically safe and standard category ib
applications
–1000 m: intrinsically safe category ia applications
–With 4 repeaters up to 9.5 km
Number of participants
in the segment (max.
126 per network)
–Non-ex: max. 32 participants per segment
–Ex ia: max. 10 participants
–Ex ib: max. 24 participants
Number of repeaters Max. 4 repeaters
Remote power supply Alternatively via the signal wires
Types of protection intrinsic safety (Ex ia/ib)
Transmission rate 31.25 kbit/s
Bus access method Publisher/subscriber
Client/server
Report/Distribution
Protocol Foundation Fieldbus H1 in acc. with IEC 61158 and
IEC 61784-1
Topology Mostly line structure, with linking assemblies (Junction
Box); star, tree and mixed topologies are also possible
Bus termination Each segment must be terminated at the beginning and
at the end by a bus terminator. In the case of branched
bus segments, the participant that is the most distant from
the transition to HSE forms the end of the bus.
8 Technical Manual Fieldbus communication
Basic principles of the Foundation Fieldbus technology
1) Depends on the type of protection and the cable specifications.
2) A maximum of 4 repeaters is permitted between participant and master.
2.3.3 Stubs
The line between a connection box and a field device is called a stub. The following
must be observed:
–In explosion-hazard areas, stubs must not be more than 30 m in length.
–Short stubs (< 1 m) count as linking devices and are not considered in the
calculation of the total bus cable length. However, this does not apply if the sum
of all short stubs amounts to 2 % of the total length of a bus.
–In non explosion-hazard areas, the maximum stub length depends on the
number of field devices.
2.3.4 Explosion-hazard area application
To ensure intrinsically safe use of the H1 bus, barriers must be installed between
safe areas and explosion-hazard areas
If networks are designed to be intrinsically safe, the “Ex i” type of protection applies.
This type of protection does not only require intrinsic safety of the connected
equipment but also relates to the entire electric circuit. The intrinsic safety of a
network depends on the connected electric circuits. The circuit with the lowest
intrinsic safety determines the intrinsic safety of the entire network. If a connected
circuit is designed to comply with Ex ib type of protection, this type of protection
applies to the entire network.
Intrinsic safety is verified using the FISCO model.
Type A Type B
Cable structure Twisted wire pair,
shielded
One or more twisted
wire pairs, overall
shielding
Core cross-section 0.8 mm² (AWG 18) 0.32 mm² (AWG 22)
Loop resistance (DC) 44 Ω/km 112 Ω/km
Characteristic impedance at
31.25 kHz
100 Ω ± 20 % 100 Ω ± 30 %
Wave attenuation at 39 kHz 3 dB/km 5 dB/km
Capacitive asymmetry 2 nF/km 2 nF/km
Group delay distortion 1.7 µs/km -
Shielding coverage rate 90 % -
Recommended maximum net-
work size (including stubs) 1)
1900 m 1200 m
Recommended maximum net-
work size (including stubs) with
repeaters 2)
1900 *2 1200 *2
Number of field devices 25-32 19-24 15-18 13-14 1-12
Stub length ≤ 1 m 30 m 60 m 90 m 120 m
Technical Manual Fieldbus communication 9
Basic principles of the Foundation Fieldbus technology
2.3.5 FISCO model
The FISCO model (Fieldbus Intrinsically Safe Concept) was developed by the PTB
(Physikalisch-Technische Bundesanstalt, the National Metrology Institute of
Germany) in order to facilitate planning, extending and installing of networks in
explosion-hazard areas. Network design in accordance with FISCO makes it
possible, for example, to exchange field devices or to extend the system without the
need for recalculation. Field devices can be exchanged by plug-and-play.
Certain constraints need to be observed in order to ensure these and other
advantages. All bus participants must comply with the FISCO model. Only one
device may feed energy into the network. Field devices may only take out energy.
When a field device is transmitting, no additional energy is fed into the bus. Field
devices that require additional auxiliary energy must be at least one type of
protection higher than the fieldbus circuit. For installation in accordance with
FISCO, corresponding control drawings are included in the instructions for use for
the respective gas detector.
Properties according to the FISCO model
2.3.6 Power supply and communication
Field devices can have their own power supply or be supplied with energy via the
bus by a feed unit. In a bus-powered network, the field devices connected to the H1
segment derive the required current from the bus cable. Field devices have a
current consumption of 10 - 30 mA at 9 - 32 V. When a field device is transmitting, it
changes its current consumption by ±10 mA at 31.25 kbit/s. At an impedance of 50
Ω, this leads to a voltage change of ±0.5 V in the network. The voltage change is
modulated onto the direct current supply of the H1 bus.
2.4 Bus access
2.4.1 Link active scheduler (LAS)
Via commands they send to the field devices, link active schedulers (LAS), also
referred to as link masters, control and schedule the bus communication.
Addressing of field devices is also controlled by the LAS. Assigned and unassigned
device addresses are cyclically queried by the LAS. As a result, new field devices
can be connected at any time. Bus systems can contain multiple LASs, which
means that a failure of an LAS can be compensated for quickly.
Ex ia/ib IIC Ex ib IIB
Cables
Loop resistance (DC) 15...150 Ω/km 15...150 Ω/km
Specific inductance 0.4...1 mH/km 0.4...1 mH/km
Specific capacitance 45...200 nF/km 45...200 nF/km
Stub length ≤ 60 m ≤ 60 m
Line length ≤ 1000 m ≤ 5000 m
Feed units Type A Type B
Max. current requirement ≤110 mA ≤110 mA
10 Technical Manual Fieldbus communication
Basic principles of the Foundation Fieldbus technology
2.4.2 Scheduled traffic
Data transmissions that are time-critical are performed by means of scheduled
traffic. This includes, for example, controlling of process variables. Scheduled data
transmissions follow a strict time schedule that is processed cyclically. This ensures
that all data are transmitted in time and that bus access conflicts are prevented. The
LAS synchronizes the field devices by means of a TD command (timer distribution).
Every field device has the time schedule in its system management. It defines the
task to be processed and the times at which data must be received or transmitted.
The LAS can also use a CD command (compel data) to request transmission of the
data.
Publisher subscriber method
When a field device transmits data, it takes on the role of the publisher, transmitting
the data that are present in the transmission buffer. The data transmitted into the
bus can then be directly read out and evaluated by field devices that are configured
as subscribers. The data are not sent to a master first which would then control the
appropriate field devices. This reduces the number of data transmissions within the
bus to a minimum.
Example:
A gas detector is continually measuring gas concentrations and communicates its
measured values cyclically. A fan is configured as subscriber of the gas detector..
2.4.3 Unscheduled traffic
Data transmissions that are not time-critical are performed by means of
unscheduled traffic. This includes, for example, the parameterization and the
diagnostics of the field devices. Free gaps in the time schedule for the scheduled
traffic are used for unscheduled traffic. During these time gaps, the LAS releases
the bus for unscheduled traffic. The LAS uses a live list and the PT command (Pass
Token) for releasing the bus. When a device receives the token, it can access the
bus until the time elapses or until it returns the token.
Live list
One after the other, all devices that are entered in the Live List receive from the LAS
the token for unscheduled traffic. The LAS sends the PN command (Probe Node) to
update the devices and addresses contained in the Live List. Newly connected
devices then respond by sending the PR command (Probe Response) and are
added to the Live List. Based on the order in the list, the device then receive the
token for unscheduled traffic.Devices are removed from the Live List if they do not
respond to the PT command issued by the LAS or immediately return the token
after 3 attempts. Changes to the Live List are communicated to all devices. This
helps prevent loss of information in the event of failure of an LAS.
Time 0: The gas detector is measuring. The fan is off.
Time 10: The LAS passes the token to the gas detector.
Time 20: The gas detector transmits its measured value or
alarm into the bus.
Time 30: The fan receives the data sent by the gas detector.
If it is an alarm, the fan switches itself on.
Technical Manual Fieldbus communication 11
Basic principles of the Foundation Fieldbus technology
2.4.4 Sequence control for scheduled and unscheduled traffic
The LAS ensures, by means of sequence control, that the scheduled traffic is not
interfered with by unscheduled data transmissions (PT Token, TD or PN command
etc.). Before an unscheduled data transmission is performed, the LAS checks the
time schedule for scheduled traffic. If unscheduled data transmission is not
possible, the LAS waits in Idle state for a gab in the time schedule. When a gap
occurs, the LAS issues the CD command. If there is enough time for a further
unscheduled action, the LAS issues further command, such as the PN, TD or PT
command.
2.4.5 Fieldbus access sublayer (FAS)
The fieldbus access sublayer builds communication relationships (VCRs) between
the bus participants. Foundation Fieldbus uses 3 VCRs. They describe
communication processes that enable speedy processing of tasks.
Publisher/subscriber
Sending and receiving of process data in scheduled traffic.
Report distribution
Sending of alarms, events and trend data in unscheduled traffic.
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12 Technical Manual Fieldbus communication
Basic principles of the Foundation Fieldbus technology
Client/server
Diagnostics and modification of field device settings in unscheduled traffic.
2.4.6 Fieldbus message specification (FMS)
Data transmission between bus participants is carried out by means of a set of
standard telegrams, which are defined by the FMS. The data contained in standard
telegrams are allocated to object descriptions. Each object description has data
from specific blocks and associated objects of the field devices. To make sure that
the object description can be correctly interpreted by the receiver, the description of
the object description itself is included in Index 0. This description is referred to as
object dictionary. The entries of indices 1-255 contain standard data types. From
index 256 upward, the telegrams contain application specific data.
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Technical Manual Fieldbus communication 13
Basic principles of the Foundation Fieldbus technology
2.4.7 Function block model
An open protocol specification is needed to ensure that devices from different
manufacturers can communicate with each other. The protocol specification defines
consistent device functions and application interfaces. The general structure of the
data transmission is assigned to 3 different blocks. In addition to the blocks, 4
objects are defined. Blocks and objects are represented in the software of the
respective field device and define the functionality of the field device. The further
subdivision by objects reduces the time for access to the data.
2.4.8 Transmission of measured values and status
The data blocks for the transmission of measured values and status are 5 bytes in
length. The first 4 bytes contain the measured value as a floating point number in
accordance with the IEEE standard. The 5th byte is used for device specific status
information. The device specific status information is given in accordance with the
NAMUR standard NE 107. If an error is present, it can be read out using the DTM.
Block types
Resource block
(RB)
Each field device has only one RB. It contains the character-
istic data of the field device, such as manufacturer, serial
number of each assembly, software version, command for re-
setting to factory settings, the status of the field device.
Transducer block
(TB)
The TB bundles parameters that describe the type of sensor
or influence the sensor. In addition, parameters for calibrat-
ing, for target gas adjustment, for alarm configuration (alarm
thresholds), maintenance and self-testing function, etc., are
integrated. Nearly the entire menu functionality is contained.
The raw data of the sensor are converted in the TB into a
measured value. The measured value is then processed in
the function block.
Function block (FB) Each field device has at least one Function block. It defines
the access to the functions of the field device. The FB also
forms the basis of the time schedules for scheduled traffic.
Objects
Link Link objects define the connections between function blocks
in a field device and in the field bus network.
Alert Alert objects document alarms and events in the field bus net-
work.
Trend Trend objects support long-term storage of function block
data.
View View objects support the representation of the function block
data and parameters. To this end, the data and parameters
are subdivided into different groups that correspond to the
respective type of task, e.g. process control, configuration,
maintenance, additional information.
Byte 1Byte 2Byte 3Byte 4Byte 5
Measured value as a floating-point number in acc. with IEEE 754 Status
14 Technical Manual Fieldbus communication
Basic principles of the Foundation Fieldbus technology
2.5 Device management
2.5.1 Device description (DD)
The device description (DD) of a field device is required for diagnostics,
maintenance and integration of the field device into the process control system. The
DD is written in a standardized file format and is included in the scope of supply of a
field device. It contains device specific parameters that are needed to integrate the
field devices with the fieldbus, including: input data, output data, data format,
amount of information and, if required, device icons that are represented in the
network tree of the control system. For the scheduled exchange of measured
values the DD suffices.
Standard DD and manufacturer specific DD
There are manufacturer specific DDs and standard DDs. The standard DD differs
with regard to the number of the individual function blocks and makes it possible to
exchange devices independently of the manufacturer. Thus it does not offer the full
functional scope of a manufacturer specific DD.
Dräger recommends the use of the manufacturer specific DD.
2.5.2 Device management in scheduled traffic
The device management in scheduled traffic is controlled by the LAS. Here, the
measured value and the status of a field device are queried. The DD is required to
integrate a field device into the scheduled traffic.
2.5.3 Device management in unscheduled traffic
In unscheduled traffic, field devices are set up by means of a PC or a service tool.
The PC is connected to the HSE segment via an interface. The interface
descriptions FDT and DTM were specified in order to capture device properties and
operating functions of the field devices across manufacturers:
FDT and DTM
The FDT/DTM concept serves the purposes of integration and management of
intelligent field devices. The concept makes it possible to configure field devices
centrally, to document their measured values and their behavior and to perform
device diagnostics.
DTMs (Device Type Managers) are software components that can be used to
implement all functions, properties and parameters of the gas detector.
Manufacturer specific DTMs also contain the complete control panel and the menu
structure of the field device.
The FDT (Field Device Tool) is a cross-manufacturer concept enabling
parameterization of different field devices using just one software. This software is a
framework application into which the required DTMs can be loaded. This concept
can be compared with the way printer drivers are loaded into an operating system.
Technical Manual Fieldbus communication 15
Basic principles of the Foundation Fieldbus technology
Communication DTM (COM_DTM)
The Communication DTM is a driver that sets up the interface between fieldbus
cable and the PC. This interface can for example be a USB-Ethernet converter. The
Communication DTM is installed within the FDT framework application.
2.6 Current and voltage on the H1 bus
2.6.1 Current calculation
The following values need to be known for the calculation:
–IS = Feed current of the power hub
–IB = Base current of each field device
–IFDE= Fault current of each field device
The maximum number of field devices on the H1 bus is a function of the feed
current of the Power hub used and the current consumption of the field devices.
The current requirement of the segment ISEG is calculated as follows: ISEG = ∑IB +
max. IFDE
A segment is permissible if IS ≥ ISEG.
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16 Technical Manual Fieldbus communication
Basic principles of the Foundation Fieldbus technology
2.6.2 Voltage at the last field device
The minimum operational voltage (9 V) must be verified at the field device that is
the most distant from the feed unit, since the cable resistance causes a voltage
drop.
The voltage is calculated using Ohm's law:
UB = US – (ISEG * RSEG)
Where: UB = Voltage at the last device
US = Feed voltage of the feed unit (manufacturer's data)
ISEG = Current requirement of the segment
RSEG = Cable resistance = bus length * specific resistance
2.6.3 Voltage calculation and line length
The following formula is used to calculate the maximum cable length for a specific
cable resistance.
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Technical Manual Fieldbus communication 17
Basic principles of the Foundation Fieldbus technology
2.6.4 Example of worst case calculation
In certain cases, the maximum line length can be negatively affected by the
distribution of the bus participants in the segment.
RL = Line resistance of line segment χ
In = Current consumption of the nth field device
Given values (from current calculation and data sheet of the cable type):
ISEG = max. direct current (incl. IFDE) = 100 mA
RL = Specific resistance of cable type A = 44 Ω/km.
To ensure proper functioning of a field device, the input voltage at the bus line must
not be lower than 9 V.
Thus the following obtains for the maximum voltage drop over the line: ULmax = US -
9V.
Example: Feed unit with Ex interface
Feed units with Ex interface supply a voltage of 12.8 V.... 13.4 V.
Thus we obtain the maximum voltage drop over the line
ULmax = US - 9 V = 12.8 V - 9 V = 3.8 V
The max. line resistance RLmax[Ω] = (ULmax/ ISEG) = 3.8 V / 0.1 A = 38 Ω.
Thus we obtain the maximum line length
[km] = (RLmax/ RL) = 38 Ω/ 44 [Ω/km] = 0.863 km
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Installation in the H1 segment - field devices in general
3 Installation in the H1 segment - field devices in
general
3.1 Grounding and shielding
Intrinsically safe fieldbus circuits are operated in floating mode, although individual
measuring current circuits may be grounded. In some cases, overvoltage protection
needs to be placed upstream. The decision as to whether overvoltage protection is
to be used and the responsibility for proper integration into equipotential bonding
lies with the customer.
Sufficient equipotential bonding must be in place for the grounding of the
conductive shielding. The grounding of the shielding protects the digital signals on
the fieldbus against high-frequency electromagnetic interference.
Dräger gas detection equipment is only approved for capacitive grounding. The
legal EMC requirements are only met if the shielding is grounded at the control
unit at one end.
There are 3 methods for the grounding of the shielding.
–Isolated installation
–Installation with multiple grounding
–Capacitive installation
3.1.1 Isolated installation (IEC 61158-2)
The grounding of the cable shielding is separate from the device grounding and is
only applied at the feed unit. The disadvantage of this method is that the bus
signals are not optimally protected against interference. The degree of interference
depends on the length and topology of the bus.
3.1.2 Installation with multiple grounding (IEC 79-13)
All cable shields and devices are grounded locally. The grounding lugs are
connected to an equipotential bonding conductor that is grounded in the safe area.
This grounding method achieves increased protection of the signals against
interference and may be used, subject to conditions, in explosion-hazard areas.
3.1.3 Capacitive installation
The cable shields are grounded via a capacitor. The capacitors have an electric
strength of 1 nF/1500 V. The overall capacity connected to the shielding must not
exceed 10 nF. A shielded and twisted cable must be used.
Capacitive grounding in non-explosion-hazard areas:
–Field devices and connection boxes are capacitively grounded between cable
shielding and earth. The capacitors are installed inside the connection boxes.
–The feed unit is grounded using the normal method.
Technical Manual Fieldbus communication 19
Installation in the H1 segment - field devices in general
Capacitive grounding in explosion-hazard areas:
–The connection box is grounded using the conventional method.
–The feed unit is capacitively grounded. The bus shield must be grounded directly
at the feed unit.
–At the Dräger gas detector, the shield is inserted into the PIN provided for that
purpose.
3.2 Termination
Passive termination is required at the beginning and end of each segment. The
termination suppresses signal reflections on the bus line. Termination is achieved
by means of a combination of a resistor and a capacitor (RC element).
3.2.1 Termination of an MBP interface (on the H1 side)
–The linking device at the beginning of the segment has an in-built bus
terminator.
–In the case of a branched bus segment, the field device that is the most distant
from the linking device forms the end of the bus and needs to be terminated.
–If the connected stubs are longer than 30 m, termination must be installed
directly at the field device.
–If the bus is extended using a repeater, the extension also needs to be
terminated at both ends.
Termination in non-explosion-hazard areas
In most connection boxes, bus termination can be activated by means of a switch.
Where this is not the case, a separate bus terminator needs to be installed.
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20 Technical Manual Fieldbus communication
Installation in the H1 segment - field devices in general
Termination in explosion-hazard areas
Connection boxes with switchable termination resistors are not permitted. The
termination resistor must have appropriate approval and is installed separately.
3.3 PD tag and addressing
PD tags (physical device tags) are alphanumeric IDs for field devices. PD tags can
be up to 32 characters long. In addition, each bus participant needs to have a
unique address. Setting of the address is performed centrally by means of FDT and
DTM. Addresses occupy ranges between 0 and 255. LASs receive addresses in
the range 1-15. Basic Devices are addressed in the range 16-247. Field devices are
automatically detected by the LAS and then receive an address from the default
address range, i.e., 248-255. Dräger gas detectors can only be used as basic
devices and are supplied ex factory with the address setting of 247 and the PD tag
(product name serial number, e.g. Polytron 8000______ ERHK-0214). If two Dräger
gas detectors are present in the same segment, one device will keep its address,
while the second device will be assigned an address from the default range.
During setting, the field devices can assume 3 states. If the field device state is not
SM_OPERATIONAL, no function block can be executed. If the address of a field
device is deleted, the field device receives a random address from the default
address range, until it is set up again. To this end, the device ID must be known at
any time.
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