Profibus PA device commissioning and maintenance - Andy Verwer

PROFIBUS PA Device
commissioning and
maintenance
Andy Verwer,
Verwer Training
& Consultancy
Ltd
Accredited PI
Training Centre
Practical Aspects of
PROFIBUS and
PROFINET in
Process. Held at
Endress+Hauser
Manchester, 29th
June 2016
PROFIBUS PA device commissioning & maintenance , Andy Verwer, page 2Practical Aspects of PROFIBUS and PROFINET in Process, 29 June 2016
Outline of presentation
This presentation will introduce the concept of profiles and in
particular the PA profile, which is mandatory for all PROFIBUS
PA devices.
The presentation will briefly explain the structure of the PA
profile and show the benefits that this can bring when working
with extensive and complex plants.
We will include a practical demonstration showing
manufacturer independent remote device access for device
which provides functions for commissioning, maintenance,
calibration and monitoring.
2

What is PROFIBUS PA?
Most people understand that:
The PROFIBUS PA protocol is exactly the same as PROFIBUS
DP. I.e. the structure and content of the telegrams are the
same.
But the PA physical layer uses Manchester Bus Powered
(MBP) wiring instead of the RS485 wiring used in DP.
However, this is not totally correct!
PA devices can have an RS485 interface.
The real difference between DP and PA is that PA devices must
adhere to the “PROFIBUS PA profile”.
The PA profile defines how the device data is organised and
accessed and defines which functions and parameters must be
provided on PA devices.
4-20mA transmission
PA was designed to replace 4-20mA technology.
With 4-20mA each device needs a separate cable and
input/output on the controller.
The IO card on the controller contains an Analogue to
Digital Converter (ADC).
PLC with
4-20mA
or 1-5V
input
24V
250Ω1-5V
4-20mA

4-20mA calibration
Transmitted signal
Measured
value
Calibrated range or
span
Minimum
Measured
Value
Maximum
Measured
Value
20mA
4mA
Example:
Temperature transmitter span =
0 to 250°C
Transmitted current = 10mA,
what is the temperature?
Fraction of range
10 4
20 4
6
16
0.375
Therefore temperature
0 0.375 250
93.75
10mA
?
PROFIBUS PA
4-20mA devices always connect to a 4-20mA input on a
remote IO unit or controller IO card.
Communication is analogue.
Scaling is done in the controller (PLC).
The controller only sees the value as a 12 or 16 bit integer
value (range 0 to 4095, or 0 to 65535).
PROFIBUS PA is quite different.
The Devices all communicate digitally.
The scaling is done in the device (i.e. the instrument).
Transmitted process values are sent as floating point
numbers, scaled and calibrated in engineering units (e.g.
°C, mBar, litres/minute, m3 etc.)

The PA Profile
The PROFIBUS PA Profile provides a mandatory specification
for all PA devices.
Defines the device functions, data organisation and
formatting.
The Process Value is always communicated in a standardised
format:
Standard floating point format for analogue values.
Standard digital format for discrete values.
Plus a standardised status value which encodes the quality
of the measurement (good, bad, usable etc.)
The profile also specifies mandatory device parameters so that
standardised tools can be used to access this data with any
manufacturer’s devices.
Data representation
The process values of PA devices are transmitted as:
32-bit floating-point values (analogue devices), or
discrete bits or bytes (switching devices).
Together with a “status byte” containing information about
the “quality” of the process value.
Typical analogue instrument or actuator value:
Byte 1 Byte 2 Byte 3 Byte 5Byte 4
Floating point number representing the
process value in “engineering units”
Status byte
representing the
quality of the value

Status byte interpretation
The status byte consists of eight bits representing signal
quality.
The most significant bit is used to indicate the overall quality
of the associated value:
= Bad (‹80hex, 12810)
= Good (≥≥≥≥80hex, 12810)
The remaining bits in the status byte give further
information on the device status.
0 X X X X X X X
1 X X X X X X X
The PA profile structures a device into “Blocks”:
A Physical Block, PB
Contains the parameters and functions of the device
hardware and installation etc.
One or more Transducer Blocks, TB
Describes the interface to the process, i.e. the sensor or
actuator characteristics.
One or more Function Blocks, FB
Contains common signal manipulation and automation
functions.
Each device also incorporates a Resource or Device
Manager.
Describes which blocks are available in the device and a look-up
table for the device parameters.
PA device model

Block header
Block header
Block header
Block header
Device
Physical block, PB
Transducer block, TB Function block, FB
Resource Manager
Directory header
List of blocks
Pointers to blocks
PB pointer
TB pointer
TB pointer
FB pointer
FB pointer
Block header
Block header Block header
parameters
parameters parameters
Parameter order
and semantics
described in PA
profile.
PA device model
The blocks can execute functions that manipulate the process
value or device state.
Each TB/FB pair is responsible for a process value, which can
be a measurement from an instrument or an actuator value to
a valve or positioner.
Each process value is exchanged with the controlling Class-1
master using normal cyclic data exchange.
The parameters of the blocks can be read from or written to
the device using acyclic functions.
These are normally accessed by a Class-2 master
(Engineering Tool),
or alternatively by the controlling Class-1 master.
Data access

Physical block
Transducer block
(Pressure)
Function block
(Analogue Input)
Sensor signal
Measured value
transmitted
cyclically to
Class-1 master
Transmitter block model
Parameters read
and written
acyclically by
Class-2 master
Process Value
Parameters Parameters
Parameters
PA device model
Pressure
Transmitter
Transducer blocks reflect the measurement or actuation that is
taking place.
Transducer blocks are available for a wide range of
instruments and actuators:
Temperature – RTD, thermocouple etc.
Pressure/differential pressure etc.
Level – hydrostatic, displacement, microwave, capacitance
etc.
Flow – head meters, electromagnetic, Coriolis etc.
Transducer blocks

Temperature transducer block
Level transducer block

Function blocks contain common signal conditioning and
automation functions.
There are currently three function blocks for inputs and two
for outputs defined in the PA profile:
Analogue input, Analogue output,
Discrete input, Discrete output,
Totaliser (for use with flow measurement),
The analogue input block is the most common block, being
used for all analogue instruments. It provides for each
measurement:
Linearisation, filtering, alarms, fail-safe action, simulation
facilities and auto/manual mode control.
Function blocks
Analogue input function block

PA engineering tools
The functions and addressing to access parameters is defined in
the PA profile.
Specialist PA engineering tools are available that can interact
with devices without requiring explicit addresses.
PA engineering tools come in two types:
EDD tools (such as Siemens PDM)
FDT tools (such as E+H FieldCare, P+F PactWare etc.)
(EDD = Electronic Device Description, FDT = Field Device Tool)
PA engineering tools
Siemens supply an extensive package for Process Automation.
Process Device Manager, PDM, provides a universal,
manufacturer-independent tool for configuration, parameter
assignment, commissioning, diagnostics and maintenance of
intelligent field devices and components.
PDM is based on EDD technology.

FDT/DTM tools
FDT is an open technology that is defined by international
standards and supported by several manufacturers (E+H
FieldCare, P+F PactWare etc.)
The FTD tools use Device Type Managers (DTMs) to establish
the required communications and to access parameters in the
different devices.
Two different types of DTM are available:
Communications DTMs (CommDTMs) – establish a
communication route to the devices.
Device DTMs – to access data within a particular type of
device.
FDT/DTM tools
ProfiTrace is a widely-used fault-finding and
commissioning tool for PROFIBUS DP and PA.
COMbricks is a widely-used modular
PROFIBUS network monitoring solution,
which incorporates a built-in ProfiTrace
analyser available over Ethernet.
These products both support a CommDTM that allows them to
be used in any FDT environment.

COMbricks
COMbricks is a modular unit from PROCENTEC, the people
who make ProfiTrace.
COMbricks is designed to be part of your PROFIBUS network
infrastructure, built in to provide:
A modular, expandable system incorporating network
components such as repeaters, hubs, DP/PA links and many
other functions.
All connected networks and segments are monitored by a head
station which incorporates a built-in ProfiTrace analyser that
monitors up to 4 separate networks with 20 segments. The
analyser communicates with standard tools over Ethernet to
provide 24/7 access and monitoring of the health of all
connected networks, segments and devices.
COMbricks also incorporates a built-in commDTM server that
allows COMbricks to be used with any standard FDT tool for
device commissioning, calibration and maintenance functions.
2
3
Head Station
with
ProfiTrace
built in
Repeater
modules with
optional
‘scope and
redundancy
PROFIBUS
DP slave
modules
IO modules
digital,
relay,
analogue
etc.
PROFINET
IO device
modules
Optical link
modules
(1 or 2
channel)
mix and match to produce the required functionality
The Modules available include:
PA module
Coupler
and/or MBP
monitor
with ‘scope
COMbricks

Our Demo
For our demo, we have a COMbricks unit consisting of a head
station, A DP repeater module and a PA coupler/link module:
1 channel
‘scope
repeater
Head
Station
PA
coupler
module
Ethernet
DP
(RS485)
PA
(MBP)
The Head Station
monitors both the DP
and PA segments via the
built-in ProfiTrace,
which communicates via
standard Ethernet.
The DP repeater module
and PA coupller/link
module together make a
transparent DP/PA
coupler which provides
access to the PA devices
for the controlling
master.
And provides access for
the FDT tools via the
built-in commDTM.
FDT/DTM
• The FDT provides a standardised framework in
which the required DTMs can be loaded and run.
• The device DTMs operate underneath the
CommDTM in order to provide a route to the
devices.
CommDTM
Device DTMs
DP
PA
COMbricks
transparent
coupler and
Ethernet
gateway
Devices
Ethernet

Profibus PA device commissioning and maintenance - Andy Verwer

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