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Specific Application Profiles

PROFIBUS stands out from other fieldbus systems primarily due to the extraordinary breadth of application options. The PROFIBUS concept has set new standards. Not only has it developed specific profiles that take into account key industry-specific user demands – it has also successfully united all key aspects across all applications in a standardized and open fieldbus system, thus ensuring full protection of existing investment.

Table 8 shows all current specific PROFIBUS application profiles as well as those pending.

5.1 PROFIdrive

The PROFIdrive profile defines device behavior and the access procedure to drive data for electric drives on PROFIBUS, from simple frequency converters through to highly dynamic servo-controls.

PROFIdrive positioning with central interpolation and position control

Fig. 21: PROFIdrive, positioning with central interpolation and
position control


The integration of drives in automation solutions is highly dependent on the task of the drive. For this reason, PROFIdrive defines six application classes, which cover the majority of applications.

With standard drives (class 1), the drive is controlled by means of a main setpoint value (for example rotational speed), whereby the speed control is carried out in the drive controller.

In the case of standard drives with technological function (class 2), the automation process is broken down into several sub-processes and some of the automation functions are shifted from the central programmable controller to the drive controllers. PROFIBUS serves as the technology interface in this case.

Slave-to-slave communication between the individual drive controllers is a requirement for this solution.

The positioning drive (class 3) integrates an additional position controller in the drive, thus covering an extremely broad spectrum of applications (for example the twisting on and off of bottle tops). The positioning tasks are passed to the drive controller over PROFIBUS and started.

The central motion control (classes 4 and 5) enables the coordinated motion sequence of multiple drives. The motion is primarily controlled over a central numeric control (CNC). PROFIBUS serves to close the position control loop as well as synchronize the clock (Fig. 21). The position control concept (Dynamic Servo Control) of this solution also supports extremely sophisticated applications with linear motors.

Distributed automation by means of clocked processes and electronic shafts (class 6) can be implemented using slave-to-slave communication and isochronous slaves. Sample applications include "electrical gears", "curve discs" and "angular synchronous processes".

PROFIdrive defines a device model as functional modules that operate together internally and which reflect the intelligence of the drive system. These modules are assigned objects that are described in the profile and defined with regard to their functions. The overall functionality of a drive is described by the sum of its parameters.

 

Designation

Profile contents

Current status of PNO guideline

PROFIdrive

The profile specifies the behavior of devices and the access procedure to data for variable-speed electrical drives on PROFIBUS.

V2

3.072

 

V3

3.172

PA devices

The profile specifies the characteristics of devices of process engineering in process automation on PROFIBUS.

 

V3.0

3.042

Robots/NC

The profile describes how handling and assembly robots are controlled over PROFIBUS.

V1.0

3.052

Panel devices

The profile describes the interfacing of simple human machine interface devices (HMI) to higher-level automation components.

V1.0D

3.082

Encoders

The profile describes the interfacing of rotary, angle and linear encoders with single-turn or multi-turn resolution.

V1.1

3.062

Fluid power

The profile describes the control of hydraulic drives over PROFIBUS. In cooperation with VDMA.

V1.5

3.112

SEMI

The profile describes characteristics of devices for semiconductor manufacture on PROFIBUS (SEMI standard).

3.152

Low-voltage switchgear

The profile defines data exchange for low-voltage switchgear, switch-disconnectors, motor starters, etc.) on PROFIBUS DP.

3.122

Dosing/weighing

The profile describes the implementation of weighing and dosage systems on PROFIBUS DP.

3.162

Ident systems

The profile describes the communications between devices for identification purposes (bar codes, transponders).

3.142

Liquid pumps

 

The profile defines the implementation of liquid pumps on PROFIBUS DP. In cooperation with VDMA.

3.172

Remote I/O for PA devices

Due to their special place in bus operations, a different device model and data types are applied to the remote I/Os compared to the PROFIBUS PA devices.

3.132

 Table 8: The PROFIBUS specific application profiles

In contrast to other drive profiles, PROFIdrive only defines the access mechanisms to the parameters and a subset of approx. 30 profile parameters, which include fault buffers, drive controllers, device identification, etc.

All other parameters (which may number more than 1,000 in complex devices) are manufacturer-specific, which provide drive manufacturers great flexibility when implementing control functions. The elements of a parameter are accessed acyclic over the DP-V1 parameter channel.

PROFIdrive V3 uses the version DP-V2 as its communications protocol with its innovative slave-to-slave communication and isochronous mode, see Chapter 3.2. Both application profiles are available on the Internet: "Profiles for variable speed drives", V2, Order-No.: 3.072; "PROFIdrive Profile Drive Technology", V3, Order-No.: 3.172.

 

5.2 PA Devices

Modern process devices are intrinsically intelligent and can execute part of the information processing or even the overall functionality in automation systems. The PA Devices profile defines all functions and parameters for different classes of process devices that are typical for signal flow - from process sensor signals through to the preprocessed process value which is read out at the control system together with a measured value status. The various steps of information processing (signal chain) and the status forming process are shown in Fig. 25.

The PA devices profile is documented in a general requirement part containing the currently valid specifications for all device types and in device data sheets containing the agreed specifications for specific device classes. The PA device profile is available in version 3.0 and contains device data sheets for the following:

  • Pressure and differential pressure
  • Level, temperature and flow rate
  • Analog and digital inputs and outputs
  • Valves and actuators
  • Analyzers

The Block Model - In process engineering it is common to use blocks to describe the characteristics and functions of a measuring point or manipulating point at a certain control point and to represent an automation application through a combination of these types of blocks. The specification of PA devices uses this function block model to represent functional sequences as shown in Fig. 22.

The following three block types are used:

 Physical Block (PB) - A PB contains the characteristic data of a device, such as device name, manufacturer, version and serial number, etc. There can only be one physical block in each device.

 Transducer Block (TB) - A TB contains all the data required for processing an unconditioned signal delivered from a sensor for passing on to a function block. If no processing is required, the TB can be omitted.

Multifunctional devices with two or more sensors have a corresponding number of TBs.

 Function Block (FB) - An FB contains all data for final processing of a measured value prior to transmission to the control system, or on the other hand, for processing of a setting before the setting process.

The following function blocks are available:

Analog Input Block (AI) - An AI delivers the measured value from the sensor/TB to the control system.

Analog Output Block (AO) - An AO provides the device with the value specified by the control system.

Digital Input (DI) - A DI provides the control system with a digital value from the device.

Digital Output (DO) - A DO provides the device with the value specified by the control system.

Block structure of a field device with multifunctionalitFig. 22: Block structure of a field device (with multifunctionality)


The blocks are implemented by the manufacturers as software in the field devices and, taken as a whole, represent the functionality of the device. As a rule, several blocks work together in an application, see Fig. 22, which shows a simplified block structure of a multifunctional field device.

The configuration corresponds to the division of a signal chain in two sub-processes:

The functionality of the first sub-process "measuring/actuating principle" (Fig. 25- calibration, linearization, scaling) is in the transducer blocks, the functionality of the second sub-process "preprocessing measured values/post-processing settings" (Fig. 21- filter, limit value control, failsafe behavior, operating mode selection) is in the function blocks.

 

Specifications in the PA Device Profile

It is only possible to show a selection of the specifications in brief. For further details, please refer to the specification or the relevant literature, for example "PROFIBUS PA" (Ch. Diedrich/ Th. Bangemann, Oldenbourg-Industrieverlag).


Illustration of the Signal Chain

The profile PA Devices specifies the functions and parameters that are related to each step of the signal chain, as shown in Fig. 25. As an example, Fig. 23 and Table 9 provide details of the step "calibration" and Fig. 24 shows the step "limit-value check".


Specification of the calibration functionFig. 23: Specification of the calibration function

Addressing Parameters

Blocks are determined by means of their start address and parameters through a relative index within the block; as a rule, these can be freely selected by the device manufacturer. For access to the parameters (for example using an operator tool) the device-specific block structures are stored in the directory of the device.


Batch Parameter Sets

For implementation of field devices in batch processes, the profile allows storage of several parameter sets even during the commissioning phase. The current batch process is then switched to the assigned parameter set during runtime.


Modular Devices

With PROFIBUS a distinction is made between compact and modular devices, whereby a function block is a "module" in this context. The PA Device profile offers a selection of function blocks for this purpose. Devices with a configured modularity are described as multivariable devices.


Devices with Several Process Variables

Process devices increasingly offer several process variables, for example using several sensors or in the form of derived variables. This is taken into account in the transducer blocks of the profile by differentiating between Primary Value (PV) and Secondary Value (SV).


Specification of the limit-value check functionFig. 24: Specification of the limit-value check function

Limit-Value Check

Part of the information processing transferred to the device is the limit-value check. For this purpose, PA Devices offers corresponding mechanisms for signaling when warning/alarm limits are exceeded or fallen below (see Fig. 24).


Value Status

A value status information item is added to the measured value, which delivers a statement of the quality of the measured value. There are three quality levels bad, uncertain and good and additional information is provided on a sub-status that is assigned to each quality level.


Fail-Safe Behavior

The PA Device profile also provides fail-safe characteristics. If a fault has occurred in the measuring chain, the device output is set to a user-definable value. Users can select between three different failsafe behavior types.

Please refer to the relevant document, the PROFIBUS Guideline "Profile for Process Control Devices", Order No. 3.042.

Signal chain in the PA device profileFig. 25: Signal chain in the PA device profile

5.3 Fluid Power

This profile describes data exchange formats and parameters for proportional valves, hydrostatic pumps and drives and is based closely on the PROFIdrive definitions. Either a parameter channel on DP-V0 or acyclic communication over DP-V1 are used for supplying device parameters.


Parameter

Parameter description

LEVEL_HI

Range of measured filling level

LEVEL_LO

CAL_POINT_HI

Section from the sensor measuring range with which the level range is mapped.

CAL_POINT_LO

Table 9: Parameters for the calibration function

Please refer to the corresponding document, the PROFIBUS Guideline "Profile Fluid Power Technology", Order No. 3.112.

 

5.4 SEMI Devices

Some kind of devices used in process automation are, together with others, also applied in semiconductor manufacturing, such as  vacuum pumps or flow meters.

The organization "Semiconductor Equipment and Materials International" did already specify a branch-specific device standard (SECS, Semiconductor Equipment Communication Standard) to which the PROFIBUS Application Profile SEMI is compatible.

SEMI is structured in 4 parts (General Definitions, Massflow Controllers, Vacuum Pressure Gauges and Vacuum Pumps).

 

5.5 Ident Systems

Ident systems is a profile for barcode readers and transponder systems. These are primarily intended for extensive use with the DP-V1 functionality. While the cyclic data transmission channel is used for small data volumes to transfer status/control information, the acyclic channel serves the transmission of large data volumes that result from the information in the barcode reader or transponder. The definition of standard function blocks has facilitated the use of these systems and paves the way for the application of open solutions on completion of international standards, such as ISO/IEC 15962 and ISO/IEC18000.

 

5.6 Remote I/O for PA

Due to their largely (fine) modular design, remote I/O devices are difficult to bring in line with the "ideal" PA Device model. For this reason, they have a special place in the field of distributed process automation. Furthermore, economic sensitivity also strongly influences the selected device configurations (modules, blocks, ...), resources (memory, records, ...) and functions (for example acyclic access). For this reason a simplified device model has been defined and the quantity framework restricted. The aim is to offer maximum support on the basis of cyclically exchanged data formats.

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