8 communication technologies

INTERNAL USE ONLY

Instrument Consultant Training

Module 8Communication Technologies

2009 Rosemount Inc.

2009 Rosemount Inc.

HART is a registered trademark of the HART Communication Foundation.FOUNDATION is a trademark of the Fieldbus Foundation.Tri-Loop is a registered trademark of Rosemount Inc.Modbus is a registered trademark of Modicon, Inc.

Table of Contents

Communication Technologies For Internal Use Only / 3 2009 Rosemount Inc.

Introduction..................................................................................................................................................... 1Performance Objective ............................................................................................................................. 1

The Importance of Communication Technologies ........................................................................................ 3Learning Objectives.................................................................................................................................. 3

Role of Communication Technology................................................................................................................ 4Transmitter Communication Components ....................................................................................................... 5

Basic Communication Components.......................................................................................................... 5Sensor ................................................................................................................................................ 5Signal Processor................................................................................................................................ 5Output Signal..................................................................................................................................... 6

Analog Communication Technology................................................................................................................ 7Analog Signals .......................................................................................................................................... 7

420 mA Signal.................................................................................................................................. 7315 psi Signal .................................................................................................................................. 7

Digital Communication Technology................................................................................................................ 8Digital Communication Protocols............................................................................................................ 8Advantages of Digital Communication..................................................................................................... 9

Decreased Wiring Costs .................................................................................................................... 9Remote Device Communication ........................................................................................................ 9Improved Accuracy in Data Transmission ........................................................................................ 9More Information from a Single Device.......................................................................................... 10

HART Communication Protocol .................................................................................................................. 11Learning Objectives................................................................................................................................ 11

HART Technology Overview ......................................................................................................................... 12Digital Process Values ........................................................................................................................... 13

How A/D Converters Work.............................................................................................................. 13How D/A Converters Work.............................................................................................................. 14

Advantages of HART Technology .................................................................................................................. 15Integration with Existing Equipment ...................................................................................................... 15

Burst Mode ...................................................................................................................................... 15Multiple Process Variables..................................................................................................................... 16Remote Device Communication.............................................................................................................. 16Transmitter Self-Diagnostics .................................................................................................................. 16Multidrop Networking ............................................................................................................................ 16Open Protocol......................................................................................................................................... 18

HART Communicators ................................................................................................................................... 19Connecting a HART Communicator to a Loop ...................................................................................... 19Electronic Device Descriptions .............................................................................................................. 20

Foundation Fieldbus Protocol ..................................................................................................................... 21Learning Objectives................................................................................................................................ 21

Table of Contents

4 / For Internal Use Only Communication Technologies 2009 Rosemount Inc.

Foundation Fieldbus Technology Overview.................................................................................................. 22Foundation Fieldbus Layers................................................................................................................... 22

Physical Layer ................................................................................................................................. 22Communications Stack .................................................................................................................... 23User Layer ....................................................................................................................................... 23

Foundation Fieldbus Blocks ................................................................................................................... 23Resource Block ................................................................................................................................ 23Transducer Block............................................................................................................................. 23Function Blocks ............................................................................................................................... 24

Advantages of Foundation Fieldbus .............................................................................................................. 26Protocol Design ...................................................................................................................................... 26Device Interoperability........................................................................................................................... 26Reduced Wiring Costs............................................................................................................................. 26Network Flexibility ................................................................................................................................. 27Control in the Field ................................................................................................................................ 27

Foundation Fieldbus Networks...................................................................................................................... 28Segments, Trunks, and Spurs .................................................................................................................. 28Network Topologies ................................................................................................................................ 29Device Communication on the Network ................................................................................................. 30Intrinsic Safety ........................................................................................................................................ 30

FOUNDATION Fieldbus and Redundancy ................................................................................................... 31FF Networks and Redundancy................................................................................................................ 31

Profibus Protocol .......................................................................................................................................... 33Learning Objectives................................................................................................................................ 33

Profibus Technology Overview...................................................................................................................... 34Profibus-FMS ......................................................................................................................................... 35Profibus-DP............................................................................................................................................ 35Profibus-PA ............................................................................................................................................ 35

Similarities to Foundation Fieldbus................................................................................................ 35Differences from Foundation Fieldbus ........................................................................................... 36

Proprietary Communication Protocols ........................................................................................................ 37Learning Objectives................................................................................................................................ 37

Proprietary Communication Protocols ......................................................................................................... 38Modicon Modbus .................................................................................................................................... 38Honeywell DE......................................................................................................................................... 38Foxboro FoxCom.................................................................................................................................... 39Yokogawa BRAIN ................................................................................................................................... 39

Table of Contents

Communication Technologies For Internal Use Only / 5 2009 Rosemount Inc.

Advantages of HART and Fieldbus................................................................................................................ 40Comparing HART With FoxCom and BRAIN ........................................................................................ 40

Open Protocol ................................................................................................................................. 40Widely Adopted in the Industry ....................................................................................................... 40

Comparing HART With DE .................................................................................................................... 41Maintained Analog Signals ............................................................................................................. 41Simultaneous Variable Transmission .............................................................................................. 41Broad Industry Support ................................................................................................................... 42

Foundation Fieldbus Added Advantages................................................................................................ 42Workbook Exercises....................................................................................................................................... 43Workbook Answers ........................................................................................................................................ 61

Introduction

Communication Technologies Page 1 2009 Rosemount Inc. For Internal Use Only

IntroductionCommunication is the transmission of information between two or more points (e.g., transmitter and controller) without alteration of sequence or structure of the information content. Communication technologies tie process control instruments together with host systems, network masters, and other nearby devices. The field of communication technology has evolved substantially over the last twenty years. The accuracy and utility of device communication continues to improve dramatically, especially over the last few years. Most recently, the trend in communication has been toward fieldbusesall-digital device networksin which individual devices are taking over network control responsibilities, directing their fellow devices, and managing entire loops in the field.

The following pages will introduce you to the range of device communication technologies commonly used in the process control industry. You will start by learning about basic analog communication technology. You will also learn about the various digital communication technologies that have appeared and evolved over the last twenty years, and the benefits and limitations of each technology.

This module contains the following seven sections:T Importance of communication technologiesT HART communication protocolT FOUNDATION Fieldbus protocolT Profibus protocolT Proprietary communication protocolsT Modbus protocolT OPC

PERFORMANCE OBJECTIVEAfter completing this module, you will be able to discuss relevant communication technologies with your customers and recommend communication technology strategies to your customers.

The Importance of Communication Technologies



LEARNING OBJECTIVESAfter you have completed this section, you will be able to:T Explain the role that communication technology plays in process controlT Identify the fundamental components involved in transmitter communicationT Define communication protocolT Explain the difference between analog and digital communication signalsT Briefly describe the key advantages of moving from analog communication technologies to

digital communication technologies


Activities

Page 4 Communication TechnologiesFor Internal Use Only 2009 Rosemount Inc.

Role of Communication TechnologySensor equipment does not generally produce usable signals on its own. Typically, a sensor will emit or regulate a small voltage or current. The fundamental job of communication technology is to transform the raw signals from transducers into intelligible values that can be transmitted to other locations such as a control room or maintenance shop.

1. The fundamental job of communication technology is to transform the raw signals from a _______________ into values that are typically transmitted to _______________________.

For the last several decades, communication technology has been continuously improving its ability to carry out this fundamental job. Transmitters and communicators are able to produce and communicate more accurate and repeatable process values every year.

Recent digital communication systems have enabled a number of additional roles, including:T Remote device maintenanceTechnicians can interact

with, test, and configure field devices from remote locations using two-way digital communications.

T Self-diagnosticsInstruments and valves can observe their own status and report problems back to a control room or maintenance shop.

2. Name three tasks that digital communication can perform.

T Process diagnosticsInstruments and valves can observe abnormal process conditions and report problems back to the control room or maintenance shop.

T Control in the fieldTransmitters can handle network traffic in the absence of a control host. Furthermore, transmitters and other devices can be linked together in complex, decision-making networks.

COMPLETE WORKBOOK EXERCISE 8.1 ON PAGE 43

1.Sensor; control room or maintenance

shop

2.Remote device maintenance,

self-diagnostics, and control in the field

Activities



Transmitter Communication Components

BASIC COMMUNICATION COMPONENTSThe basic communication components are:

3. Name the basic communication components.

T TransducerT Signal processorT Output signal

Figure 8.1 illustrates how the basic communication components interoperate.

Figure 8.1: Basic Communication Components

Sensor4. What is the function of a

sensor?The sensor interacts with the physical process and generates an electrical signal usable by a signal processor (i.e., transmitter) For example, a pressure sensor might convert pressure into millivolts.

Signal ProcessorWithin a transmitter, a signal processor accepts the raw electrical signal from a sensor, performs calculations on the signal according to preset values (e.g., range, span), and sends out a new electrical signal suitable for transmitter output.

Output signal

Signalprocessor

Transducer(converts the physical process signal into an electrical signal process)

Physical processsignal (e.g., pressure,

temperature)

Signal uses a communication protocol (e.g., 420 mA, HART, Fieldbus)

3.Sensor, signal processor, and output

signal

4.To convert a physical process signal

into an electrical signal.

Activities



Transmitter Communication ComponentsAnalog-to-Digital ConverterThe signal processor may convert the incoming analog signal from the transducer to a digital signal before processing the signal. By converting the raw signal to a digital value, the processing electronics can perform more sophisticated calculations and produce a more accurate value than with a pure analog signal.

5. Define communication protocol.An analog-to-digital (A/D) converter changes an analog signal into an equivalent digital signal.

Output Signal6. What does an A/D converter

do?The output signal component transmits the electrical impulse from the signal processor to a host system or to the field device network.

The output signal conforms to the specification of a communication protocol. A communication protocol is a set of rules that two devices use to talk to each other. The rules enable the output signal sent by the transmitter to be received

7. Why are D/A converters still in use today?

and correctly interpreted by a host system or other devices on the network. Most transmitters use communication protocols that are based on a small range of electrical signals. For example, a transmitter might use the signal 6 milliamps (mA) to mean steam is moving through the pipe at a rate of 50 cubic feet per minute.

Digital-to-Analog ConverterPrior to sending the output signal, the transmitter may convert a digital value (used internally by the signal processor) to an analog value. Transmitters convert digital values to analog values because many process control devicesuse analog signals for monitoring and process control.

A digital-to-analog (D/A) converter changes a digital signal into an equivalent analog signal.


5.A set of rules that two or more devices

use to talk to each other

6.Convert analog signals into digital

signals

7.Some process control devices require

analog signals

Activities



Analog Communication TechnologyAnalog signals are signals which can be continuously varied across a scale of values. Analog signals change in non-discrete stepsany value within the minimum to maximum range of the device is possible.

ANALOG SIGNALSThe process control industry uses two main analog signals:T 420 mAT 315 psi

8. What are the two main analog signals?

420 mA SignalThe 420 mA signal is by far the most prevalent analog signal in the process control industry. This signal varies the current of an electrical signal to convey information. The 420 mA range represents the normal 0100% range of the value being transmitted. Failure/alarm conditions are transmitted using mA values outside this normal range (i.e., signals between 04 mA and/or above 20 mA).

9. Why does the 4-20 mA signal use 4 mA for its lowest value?

Using 4 mA as the lowest value in the range is primarily beneficial for diagnostic purposes. Users calibrate the transmitter to output 4 mA when the process condition is in a zero state (e.g., empty tank). In a system where the zero state corresponded to 0 mA, as with 0-20 mA, a reading of 0 mA may represent a valid reading, or be the result of a device failure.

315 psi SignalThe 315 psi signalsometimes called the pneumatic signaldoes not vary an electrical signal to convey data. Instead, pneumatic systems use compressed air; the greater the air pressure, the higher the value communicated.

Pneumatic signals are often used with dedicated devices such as switches and valves.

8.4-20 mA and 3-15 psi

9.The 4 mA signal is primarily used for

diagramatic purposes


Activities


Digital Communication TechnologyDigital signals are signals that change only in discrete steps. A digital signal does not continuously change like an analog signal; digital signals jump directly from one value to the next. For example, a digitally-tuned radio can be tuned to 94.7 FM or 94.8 FM but it cannot be tuned between those two steps.

10. True or False? Tuning the radio frequency by pressing a control button is an example of digital control.

Because process values are inherently analog, transmitters must obtain a digital process value by sampling the analog process value many times per second, which causes the value to step to discrete values. Figure 8.2 illustrates digital process values.

Figure 8.2: Digital Process Values

DIGITAL COMMUNICATION PROTOCOLSThe process control industry uses a wide variety of digital protocols for device communication. Four of the most common protocols are:T HARTT FOUNDATION FieldbusT ProfibusT Modbus

Digital communication protocols are explained in detail throughout the remainder of this module.

Analogprocess

value

Sampleddigitalvalues

Digitalprocess

value

10.True

11.b, c, d, e

11. Which of the following are commonly used digital communication protocols? Select all that apply.

a. 420 mAb. FOUNDATION fieldbusc. HARTd. Profibuse. Modbus


Digital Communication Technology


ActivitiesADVANTAGES OF DIGITAL COMMUNICATIONDigital communication technology offers significant advantages over simple analog technology. Some of the most important advantages of digital communication are:T Decreased wiring costsT Remote device communicationT Improved accuracy in data transmissionT More information from a single device

Decreased Wiring Costs12. Name three advantages of

digital communication.Digital communication allows multiple transmitters to operate on the same set of communication wires, or band of the radio spectrum. Because each transmitter does not need to be individually wired to a control system, the wiring cost per transmitter is lower.

Remote Device CommunicationTwo-way digital communication permits hosts (e.g., hand-held devices, control systems, asset management systems) to communicate with transmitters either locally or from a remote location. Thus, users can perform the following functions from a remote location:T Diagnose the health of the field device, process

equipment, or the process itselfT Determine a transmitters current status, which may

include predictive maintenance informationT Conduct a loop testT Commission a new device

Improved Accuracy in Data TransmissionA digitally transmitted value is either accurately received by the control system or not received at all. Environmental influences (e.g., electrical interference) never alter the values of digitally transmitted data. Environmental influences do affect data transmitted with an analog protocol (e.g., 420 mA).

12.Decreased wiring costs, remote device

communication, improved reliability in

data transmission, and more

information from a single device

Activities



Digital Communication TechnologyMore Information from a Single DeviceAn analog signal represents a single parameter. A digital signal can contain many different parameters, each uniquely identified within the digital message.


HART Communication Protocol


HART Communication ProtocolLEARNING OBJECTIVESAfter completing this section, you will be able to:T Briefly describe how HART devices communicateT Briefly describe the analog-to-digital (A/D) and digital-to-analog (D/A) conversion processT Explain the key advantages of HART communication technology over simple analog

communication technologyT Briefly describe burst modeT Briefly describe multidrop networking with HART devicesT Explain how a HART communicator is connected to a control loopT Define device descriptionT Briefly describe wireless HART


Activities


HART Technology OverviewTransmitters capable of using HART technology can overlay a digital signal on top of an analog signal. The HART signal conveys digital information (a series of 0s and 1s) by using frequency shift keying. A frequency of 1100 Hz equals a 1, and a frequency of 2200 Hz equals a 0. Because the average modulating current value is zero, the digital HART signal has no effect on the regular analog signal. Figure 8.3 illustrates frequency shift keying.

1. Which technique does HART technology use to convey digital information?

Figure 8.3: Frequency Shift Keying

2. What is the minimum resistance that must be present in the loop to establish HART communication?

A minimum of 250 must be present in the loop for HART communication to work. The resistance is required so that the digital HART signal will create enough voltage to be recognized by a host system or HART communicator.

Analog signalHART

signal


1.Frequency shift keying

2.250 ohms


HART Technology Overview


ActivitiesDIGITAL PROCESS VALUESHART-capable transmitters use digital process values. Therefore, the transmitter must convert the analog value from the transducer to a digital value (A/D conversion). And because HART-capable transmitters send a digital and an analog output signal, the transmitter must also convert the output signal from a digital value back to an analog value (D/A conversion).

3. What factors can affect the quality of an A/D conversion?

Figure 8.4 illustrates how the components of a HART-capable transmitter work together.

Figure 8.4: HART Communication Components

How A/D Converters WorkHART-capable transmitters change analog transducer information into digital information by passing the analog signal through an A/D converter. A/D converters work by sampling an analog signal many times per second. Each time the analog signal is sampled, the A/D converter records a digital value that is as close as possible to the analog value.

Two factors affect the quality of digitally sampled values:T Sampling rateThe number of times per second that the

analog signal is sampledT Sampling precisionThe smallest change in the analog

value that will cause the digital value to change

Output signal

Signalprocessor

Transducer

Mechanicalsignal

Signal uses an analog protocol(e.g., 420 mA) and the HART protocol

A/Dconverter

D/A converter

Digital information (i.e, HART values)

3.Sampling rate and sampling precision

Activities



HART Technology OverviewFigure 8.5 illustrates the sampling rate and sampling precision of an A/D conversion. The higher the sampling rate and sampling precision, the closer the digital signal will be to the original analog signal.

4. What determines the quality of the output of a D/A conversion?

Figure 8.5: Sampling Rate and Precision

How D/A Converters WorkTo produce an analog output, HART-capable transmitters use a D/A converter to convert digital process information into an analog signal. A D/A converter produces an analog wave based on the digital samples taken during the A/D conversion.

Figure 8.6 shows an analog signal produced by a D/A converter. The signal comprises many individual steps that represent the individual digital values recorded during the A/D conversion.

Figure 8.6: Analog Output of a D/A Converter

Analogtransducer

signal

Samplingprecision(10 steps)

1 sec 2 sec 3 sec

Sampling rate(10 samples per second)

Analog output

1 2 3

Time (seconds)


4.The quality of the original A/D

conversion and the quality of the D/A

conversion

Activities



Advantages of HART TechnologyHART communication technology offers additional capabilities over analog-only communication. Some of the most important capabilities are:

5. Which of the following are significant capabilities of HART technology? Select all that apply.

T Compatible with existing analog equipmentT Multiple process variablesT Remote device communicationT Transmitter self-diagnosticsT Multidrop networkingT Open protocolT Equipment and process diagnosticsT Wireless communications

INTEGRATION WITH EXISTING EQUIPMENTA key capability of HART technology is that it can be used with existing equipment that uses the 420 mA signaling standard, because HART devices can transmit data both as an analog signal and as a digital signal at the same time. Therefore, HART technology can be used with over 90% of the equipment installed today, including control systems, calibration equipment, and other maintenance tools.

Burst Mode6. The purpose of burst mode is to

enable the HART device to send data continuously / intermittently that is not requested by the ___________.

Burst mode is a user-selectable HART option that enables the HART device to continuously send data in digital form without the primary host requesting the data. In normal mode, a HART device can typically complete two message transactions per second; in burst mode, a HART device can complete three or more message transactions per second.

The Model 333 Tri-Loop also uses burst mode transmission to receive data from multivariable transmitters. The Tri-Loop converts the burst mode data into three analog signals that can be used by analog host systems.

5.a, b, c, e, f

6.Continuously; primary host

a. Integration with existing equipment

b. Multiple process variablesc. Remote device

communicationd. Safely used in any hazardous

area withou approvale. Transmitter self-diagnosticsf. Equipment and process

diagnostics

Activities



Advantages of HART TechnologyMULTIPLE PROCESS VARIABLESHART-capable transmitters send two output signals simultaneously: a regular analog output signal and a digital HART signal overlayed on the analog signal. Therefore, HART-capable transmitters can send two (or more) process variables at the same time. The HART digital signal alone is capable of sending up to four variables simultaneously to support multivariable transmitters and more complex devices (e.g., analyzers, valve positioners).

REMOTE DEVICE COMMUNICATION7. True or False? HART

communicators are commonly used to communicate remotely with HART devices.

To configure or test an analog-only transmitter, a technician must physically go to the transmitter and use analog adjustments on the device itself. HART-capable transmitters can engage in two-way digital communication, which means a technician can make adjustments to a transmitter from anywhere in the loop.

The most common methods for remote HART communication are a hand-held communicator such as the Rosemount Model 375 HART Communicator. HART communicators are discussed later in this module.

TRANSMITTER SELF-DIAGNOSTICSThe digital electronics in a HART-capable transmitter or an online asset management application such as AMS Device Manager allow the transmitter to periodically run its own self-test suite. If the transmitter locates a problem, it can communicate the error condition in its digital HART information.

Transmitter self-diagnostics can significantly aid technicians with device maintenance by proactively reporting problems to an asset management system.

MULTIDROP NETWORKINGAnalog-only transmitters must be individually wired to a control system. By contrast, up to 15 HART-capable transmitters can share a single analog loop in a networking configuration called multidrop. Figure 8.7 shows a HART

7.True


Advantages of HART Technology


Activitiesmultidrop network. When on a multidrop network, transmitters can only communicate using digital HART signals; the analog signal for each device is fixed at 4 mA.

Figure 8.7: HART Multidrop Network

Each transmitter on a multidrop network identifies itself with a unique polling address from 1 to 15 or from its unique TAG ID. The output of each transmitter is accompanied by its network address, which allows the control system to differentiate the data of one transmitter from another. The network address also allows a technician to engage in two-way communication directly with a particular transmitter on the network.

Multidrop networking has a number of key advantages, including dramatically reduced wiring costs, the ability to communicate easily with many devices, and the improved reliability of a digital-only network.

Due to the limited communication speed of the HART protocol in a multidrop network, it is typically used only for monitoring applications, such as level and temperature.

Power supply

2 3 4 1

HART-capable transmitters

Digital communication only

Activities



Advantages of HART TechnologyOPEN PROTOCOL

8. What is an open protocol?HART technology is an open protocolit is openly published and is not controlled by a single vendor. Therefore, users of HART technology can be assured that the technology will remain stable and well supported by their suppliers long term. Other benefits of an open protocol include:T Competitive, market-based pricingT Several price/performance options for software and

hardwareT Lower maintenance and training costsT Continued product evolution and innovation


8.A protocol that is openly published and

is not owned by a single vendor.

Activities



HART CommunicatorsThe most common tool used to configure and test HART-capable transmitters is a HART communicator, such as the Model 375 HART communicator. HART communicators can engage in two-way communication with any HART-capable transmitter on a loop.

CONNECTING A HART COMMUNICATOR TO A LOOP

9. Where can a HART communicator be connected in a control loop?

A HART communicator can be connected anywhere in the loop across a minimum loop resistance of 250 (Figure 8.8).

Note: Even if there is 250 resistance in the loop, if the connection is not parallel to this load, communication cannot be established.

Figure 8.8: Connecting a HART Communicator to a Loop

9.Anywhere across a minimum loop

resistance of 250 ohms

Activities



HART CommunicatorsELECTRONIC DEVICE DESCRIPTIONSHART communicators recognize HART-capable transmitters

10. An electronic device description is:

by using device descriptions. Electronic device descriptions (EDDs) are electronic files that list a particular transmitters capabilities and modes of operation. EDDs allow HART communicators to know about and configure all of a transmitters features.

A HART communicator can be updated with new EDDs at any time. New EDDs let a communicator recognize new transmitters or keep up-to-date with changes in the way transmitters work.


a. A data sheet that describes the cpabilities of the HART communicator.

b. A file that describes the HART communicators modes of operation.

c. A file that describes a transmitters capabilities and modes of operation.

d. A data sheet that describes a transmitters functional capabilities.

10.c

Foundation Fieldbus Protocol


FOUNDATION Fieldbus ProtocolLEARNING OBJECTIVESAfter completing this section, you will be able to:T Define physical layerT Define function blockT Briefly describe the function of the resource block and transducer blockT List the most common FOUNDATION Fieldbus function blocks and their usesT List the key benefits of FOUNDATION Fieldbus technology over other types of device

communicationT List three restrictions of FOUNDATION Fieldbus networksT Define network topologyT Briefly describe how instruments communicate on a FOUNDATION Fieldbus networkT Explain how intrinsic safety concerns impact a FOUNDATION Fieldbus network


Activities


FOUNDATION Fieldbus Technology OverviewFOUNDATION Fieldbus (FF) is a two-way, digital-only communication protocol. FF provides an open, configurable system for connecting many different process control devices on a single network.

FOUNDATION FIELDBUS LAYERS1. Name the three layers of FF

operation.FF communication is logically divided into three layers:T Physical layerT Communications stackT User layer

Figure 8.9 illustrates the three FF communication layers.

Figure 8.9: FOUNDATION Fieldbus Layers

Physical Layer2. True or False? H1 and H2 are

the two speeds of FF.The physical layer handles the physical connections necessary to enable FF communication. The wiring connections for power and data exchange are part of the physical layer. The physical layer converts signals between the FF network and the communications stack.

The physical layer of an FF network segment can be either H1, which operates at 31.25 Kbits/second, or FF HSE (high-speed ethernet), which operates at 100 Mbits/second or faster. H1 and HSE were specifically designed as complementary networks. H1 is optimized for traditional process control applications using two-wire, bus-powered devices. HSE is designed for use with field-powered devices that have large amounts of data to transmit. HSE can also provide interconnectivity for high-data/high-performance control applications and plant information integration.

Communicationsstack

User layer

Physical layer

FF network

1.Physical layer, communication stack,

and user layer

2.False


Foundation Fieldbus Technology Overview


ActivitiesCommunications Stack3. What job does the

communications stack perform?The communications stack handles the FF network communication. The communications stack holds a queue of outgoing network messages, receives incoming mesasages, schedules time on the network for broadcasting those messages, and negotiates sending unscheduled network messages.

User LayerThe user layer controls the transmitter-human interface elements, such as transmitter configuration and alarms. The user layer is represented as function blocks. For example, two input blocks that hold the data from two temperature sensors can be linked into a mathematical block that averages the two temperatures. The user layer also provides function blocks used for monitoring and closed loop control.

4. True or False? The transducer block provides information about a devices status to control systems.

FOUNDATION FIELDBUS BLOCKSThe three main types of block contained in an FF device are:T Resource blockT Transducer blockT Function blocks

Resource Block5. Which block retrieves sensor

information and transfers it to the other block?

The resource block describes the resources that a device can provide to an FF network. For example, the resource block might list the function blocks available in a transmitter. The resource block provides the control system with information needed to recognize a devices capabilities. The key function of the resource block is to provide information about a devices status to control systems and to other applications that require the information.

Transducer BlockThe transducer block is the interface between a sensor or actuator and the function blocks in the transmitterfunction blocks can only interact with sensor or actuator data through the transducer block.

Transducer blocks are used to define the sensor type, perform sensor calibrations, configure LCD displays, support diagnostic functions, and perform other tasks.

a. It handles network communication.

b. It controls the transmitter-human interface elements.

c. It regulates the flow of signals to different Fieldbus blocks.

3.a

4.False; the resource block provides

information about a devices status to

control systems

5.Transducer block

Activities



Foundation Fieldbus Technology OverviewFunction Blocks

6. True or False? A transmitter may need to use an AO function block because some control devices may need to reduce an analog signal from the transmitter.

Function blocks provide the mechanism for acquiring, manipulating, selecting, sharing, and using information to monitor or control a process. Function blocks are interoperable computing elements used for monitoring and process control. They are interoperable since blocks from any device and any supplier can be used together.

The Fieldbus Foundation defines a very large number of function blocks. The most common function blocks are:T Analog input blockT Analog output blockT Proportional/integral/derivative block

Analog Input BlockThe analog input (AI) block obtains sensor data from the transducer block, optionally performs scaling algorithms, and sends out a digital process value. The AI block also reports a status of Good, Bad, or Uncertain based on its confidence in the process value.

7. Which of the following is an example of a PID function block in use?

The AI block is used with devices that measure a continuously varying process. Devices may have more than one AI block to handle multiple sensors.

Analog Output BlockThe analog output (AO) block accepts a digital process value as its input, optionally performs scaling and alarming, and sends a digital value to a transducer block. The transducer block then produces the appropriate signal to drive a final control element such as a valve.

Proportional/Integral/Derivative BlockThe proportional/integral/derivative (PID) block operates like the cruise control of an automobileit reads a digital process value, compares the value against a predefined setpoint, and sends out a correctional value based on the PID algorithm. The PID block is useful for feedback loops. For example, a process may require a constant flow rate even if the pressure in the process changes. In the past, the PID block was executed in the control system. FF lets the user decide where the PID block is executed: in the control system, an instrument, or a final control element.

6.False

7.b

a. Controlling the radio signal with a frequency knob

b. Controlling a valve to keep flow in a process constant

c. Controlling the flow of two liquids manually by monitoring the transmitter readings

d. Controlling the flow of current with a fuse


Foundation Fieldbus Technology


ActivitiesSignal Characterizer (SGCR) Function BlockThe Signal Characterizer (SGCR) function block characterizes or approximates any function that defines an input/output relationship. The function is defined by configuring as many as 20 X-Y coordinates. The block interpolates an output value for a given input value using the curve defined by the configured coordinates, i.e., strapping table.

Input Selector (ISEL) Function BlockThe Input Selector (ISEL) function block can be used to select the first good, maximum, minimum, or average of as many as eight input values and place it at the output. The block supports signal status propagation.

Integrator (INT) Function BlockThe Integrator (INT) function block integrates one or two variables over time. The block compares the integrated or accumulated value to pre-trip and trip limits and generates discrete output signals when the limits are reached.

Arithmetic Function BlocksThe Arithmetic function block provides the ability to configure a range extension function for a primary input and applies different arithmetic types as compensation.

The Arithmetic functions include:T Flow Compensation LinearT Flow Compensation Square RootT Flow Compensation ApproximateT BTU FlowT Traditional Multiply and DivideT AverageT SummerT Fourth Order PolynomialT Simple HTG Compensate Level



Activities


Advantages of FOUNDATION FieldbusFF offers substantial advantages over other communication protocols. Some of the most important advantages of FF technology are:

8. True or False? One of the reasons protocol design is a meaningful advantage of FF is that FF offers better process control tools than other protocols.

T Protocol designT Device interoperabilityT Reduced wiring costsT Compatibility with existing plant wiringT More accurate and reliable process control

PROTOCOL DESIGN9. Why do FF devices need less

wiring than analog devices? Select all that apply.

FF is the only all-digital device communication protocol specifically designed for the process control industry. As such, it offers better process control tools (i.e., function blocks) and more useful communication and network options than other protocols.

Furthermore, FF is an open protocolit is openly published and not controlled by a single vendor. Therefore, users of FF technology can be assured that the technology will remain stable and well supported by their suppliers.

DEVICE INTEROPERABILITYAll FF devices are interoperable by design. Any FF device can be plugged into any FF network and be automatically recognized.

REDUCED WIRING COSTSFF devices require far less wiring overhead than their analog counterparts. FF devices need less wiring because they:T Can be powered by the same wires they use to

communicate (i.e., bus-powered devices)T Share network segments with other FF devicesT Require fewer control system components

FF wiring, as a consequence, costs only a fraction of the cost of wiring an equivalent number of analog instruments.

8.True

9.b, c, d

a. FF devices have short distances between network segments

b. FF devices are bus-poweredc. Multiple F devices can exist

on a single pair of wiresd. FF devices need fewer

control system components


Advantages of Foundation Fieldbus


ActivitiesNETWORK FLEXIBILITY10. True or False? The flexibility

of FF networking gives minimum control of wiring and placement of devices.

FF technology allows customers to configure their device networks into a wide variety of different topologies, unlike traditional analog point-to-point installations (see Network Topologies on page 29). No matter where a device is placed on an FF network, the device will announce itself to the network and receive a unique network ID.

11. True or False? Control in the field is characterized by control distributed within dedicated control systems.

The flexibility of FF networking gives customers the maximum amount of control in wiring and device-placement decisions.

CONTROL IN THE FIELDFF is the only communication technology that provides the capability to perform basic and advanced regulatory control and discrete process entirely in the field. Control in the field

12. Which of the following are benefits of control in the field? Select all that apply.

means that control is distributed among field devices instead of within dedicated controllers. Control loops can be implemented on the FF segment, which increases the response speed of the control loop, resulting in better process control.

FF does not stipulate that control functionality must be located in the fieldinstead, users determine where control will be distributed based on their specific application needs. Some of the benefits of distributed control include:T ReduncancyThe failure of a control system does not

cripple closed loop control.T Reduced control costsBecause the devices themselves

are controllers, there is no need for additional controller resources in the control system.

T Greater control adaptabilityNew devices can be added online to implement new control strategies without affecting the operation of the other devices and control strategies on the segment.

T Increased reliabilityField devices are a more reliable platform from which to implement regulatory control. There are fewer failure points in field-based control, resulting in a lower failure rate.


10.False

11.False

12.a, b, c, e

a. Increased process availabilityb. Reduced control costsc. Greater control adaptabilityd. Increased safetye. Increased reliability


Activities


FOUNDATION Fieldbus Networks

SEGMENTS, TRUNKS, AND SPURSAn FF network (or segment) consists of one trunk and one or more spurs. Figure 8.10 illustrates a trunk and several spurs in an FF segment.

Figure 8.10: FOUNDATION Fieldbus Segment

13. What is the maximum cable length of an FF segment without FF repeaters?

FF segments have the following characteristics:T Every FF segment must have two terminators, one

mounted as close to each end of the segment as possibleT Each segment requires a power conditioner to prevent

messages on one segment from passing through shared components such as power supplies to other segments.

14. What acts as a limitation on the spur length?

T The maximum length of all FF wires on a segment cannot exceed 1900 m (6234 ft), although this distance can be extended with the use of FF repeaters

T An FF segment can support a practical limit of 16 bus-powered devices (or 32 individually-powered devices)

Spur length is limited by how many devices are on the spur. Table 8.1 lists maximum spur length.

Terminator

Trunk

Spur

Spur

Power supply and conditioner

Number of Devices on the Spur Maximum Spur Length

1 120 m (394 ft)

2 90 m (295 ft)

3 60 m (197 ft)

4 30 m (98 ft)

Table 8.1: Maximum Spur Length

13.1900 m (6234 ft)

14.The number of devices on the FF spur


Foundation Fieldbus Networks


ActivitiesNETWORK TOPOLOGIESThe network topology is the shape of the network. The three most common network topologies used by FOUNDATION Fieldbus are:T Point-to-pointT TreeT Branch

15. Network topology can be defined as the size / shape of the network.

Figure 8.11 illustrates the three common network topologies.

Figure 8.11: Three Common Network Topologies

Different network topologies can be combined to form complex types of networks. For example, one segment of a branch network could be the base of a tree network.

Point-to-point

Branch

Tree

Junctionbox

15.Shape

Activities



Foundation Fieldbus NetworksDEVICE COMMUNICATION ON THE NETWORK

16. What device schedules the communication on an FF network?

To keep all of the FF devices on the network communicating in a coordinated manner, communication is precisely scheduled by a device called the link active scheduler (LAS). The LAS is not a special instrument; any FF device (or a control system) can be the LAS, but only one LAS can be active on each FF segment. When each devices turn comes up on the schedule, that device sends data for a limited amount of time. If the primary LAS fails, a back-up LAS can take over and prevent an interruption in network communication.

INTRINSIC SAFETYFF network segments can be made intrinsically safe by using safety barriers between the segment and the rest of the network. Individual safety barriers support two to four devices. Multiple safety barriers can be used on a single fieldbus segment. The exact number is dependent upon several device characteristics (e.g., the I.S. classification, cable type, or power consumption).

16.LAS

Activities



FOUNDATION Fieldbus and Redundancy

FF NETWORKS AND REDUNDANCYFF networks can easily be made more secure and robust than a conventional 4-20 mA point-to-point wired system.

Using the control in the field capabilities of the field devices allows the primary control loops to be executed completely outside of the traditional controller. The ability of the devices to provide backup Link Active Scheduling for the H1 segment means that if communication is lost within the central control system, the loops will continue to function normally without any interruptions. This in itself will result in an increased availability of the overall system and a higher MTBF, usually making additional component redundancy unnecessary.

Overall control reliability depends on the reliability of the H1 segment wires, the power supply/conditioner, field devices, and terminators. FF does not support cable redundancy, but as the wire has the lowest complexity level and under normal conditions the lowest failure rate, this is usually not an issue.

Available FF redundant capabilities include:T Measurement devicesT ValvesT Segment power supplies and conditionersT Backup Link Active SchedulerT Distributed function blocksT Host H1 interface


Profibus Protocol


Profibus ProtocolLEARNING OBJECTIVESAfter completing this section, you will be able to:T List the three major types of Profibus and their usesT List the commonalities between FOUNDATION Fieldbus and ProfibusT List the key differences between FOUNDATION Fieldbus and Profibus

Profibus Protocol

Activities


Profibus Technology OverviewProfibus, like FF, is a fieldbusa two-way, digital-only communication protocol. Profibus is fundamentally designed to meet high-speed factory automation needs; one of the protocols variants has been adapted for process control use.

1. Name the Profibus variants.Profibus is made up of three different variants, each with a different purpose. The three protocols are:T Profibus-FMST Profibus-DP

2. Which Profibus variant directly competes with FF?

T Profibus-PA

Figure 8.12 illustrates Profibus topology.

Figure 8.12: Profibus Topology

Profibus-PA is the Profibus variant that directly competes with FOUNDATION Fieldbus.

PLC Power supply

Profibus-FMS(or ethernet)

Profibus- DP

Profibus- PA

Network master device

Discrete devices

DP to PAconverter

Controlvalves and

transmitters

1.Profibus-FMS, Profibus-DP, and

Profibus-PA

2.Profibus-PA

Profibus Protocol

Profibus Technology Overview


ActivitiesPROFIBUS-FMSProfibus-FMS (Fieldbus Message Specification) is a protocol that is designed for communication between controllers/PLCs, engineering stations, operating stations, or other high level devices. Profibus-FMS is a multimaster protocolany or all of the devices on the network can be masters.

PROFIBUS-DP3. Which Profibus variants

communicate using high-speed signals?

Profibus-DP (Decentralized Periphery) is a distributed I/O protocol that is best suited for high-speed, discrete device automation. In a Profibus-DP network, master devices continuously poll slave devices. Like Profibus-FMS, Profibus-DP is a multimaster system. However, Profibus-DP does not allow master-to-master communication.

PROFIBUS-PA4. How is the Profibus-PA similar

to the FF?Profibus-PA (Process Automation) is the only Profibus variant designed for process control. Profibus-PA attempts to address the same applications and market as FF H1.

Unlike Profibus-FMS and Profibus-DP, the Profibus-PA variant does not use high-speed communication signals and cannot coexist with the other two variants on the same network. Communication between a Profibus-PA segment and a Profibus-DP segment requires a network gateway known as a linking device or coupler.

Similarities to FOUNDATION FieldbusProfibus-PA is similar to FF in two main ways:T Physical layerProfibus-PA uses a physical layer that is

identical to the physical layer used by FF H1 (IEC 61158-2)

T Bus-powered, I.S. devicesBecause Profibus is electrically identical to FF, the I.S. options are identical as well

3.Profibus-FMS and Profibus-PA

4.It has a physical layer, bus-powered,

and uses I.S. devices

Activities


Profibus Protocol

Profibus Technology OverviewDifferences from FOUNDATION FieldbusProfibus-PA differs from FF in several important ways, including:

5. True or False? Reliance on function blocks puts Profibus-PA network structures at a disadvantage in comparison to FF networks.

T Protocol designProfibus was not originally designed for process control. Profibus-PA is a variant of Profibus that has been adapted to meet the physical and elecrical requirements of process plants. FF is specifically designed to meet the needs of the process control industry.

T Network structureProfibus-PA is stricter and more hierarchical in its network requirements. Profibus-PA, like traditional analog communication technology, puts all of the control into network masters and central control systems. FF allows the control to be distributed to the field devices.

T Network managementTechnicians must manually control Profibus-PA device addresses and host configurations; address conflicts can disrupt a Profibus-PA network. FF networks automatically assign device addresses.

6. What characteristic of the Profibus-PA network communication puts it at a disadvantage to the FF network structure?

T Network communicationProfibus PA is a master-slave network. Devices can only communicate on the bus when told to by the bus master, usually the control host. FF synchronizes communication among all field devices and the host. In addition, FF provides a timestamp, while Profibus PA does not.

T Network modificationsProfibus networks must be taken offline for modifications. FF allows online modifications for both control and monitoring purposes.

T Function blocksProfibus PA does not support function blocks in field devices.

T TAG searchProfibus only provides identification by device address; FF allows devices and function blocks to be identified through unique tags.

T TrendingFF devices can maintain a local trend file that can be accessed by the host; Profibus PA devices cannot.

T Data integrationProfibus PA communications must pass through several layers of networks between the field and the end user/application. This imposes communication delays and reduces reliability.


5.False

6.The Profibus-PA network puts all of the

control into the network masters and

central control systems

Proprietary Communication Protocols


Proprietary Communication ProtocolsLEARNING OBJECTIVESAfter completing this section, you will be able to:T Briefly describe the following communication protocols in terms of their basic technology and

common implementation: Modicon Modbus Honeywell DE Foxboro FoxCom Yokogawa BRAIN

T List the principal differences between Honeywell DE and HARTT List the primary advantages of FOUNDATION Fieldbus over the protocols listed above


Activities


Proprietary Communication ProtocolsDevice manufacturers have developed a large number of proprietary (i.e., closed, vendor-owned) digital communication protocols. Four of the most common other protocols are:

1. How is Modbus most frequently used?

T Modicon ModbusT Honeywell DET Foxboro FoxComT Yokogawa BRAIN

MODICON MODBUSModbus is a digital, low-level, master-slave device communication protocol. A Modbus master queries slave devices with commands, such as a command to read a process variable. Modbus is primarily used to communicate control and monitoring data.

2. True or False? The Modbus protocol is available to users and manufacturers under a royalty-free license.

Modbus operates independently of a devices physical layer. A device can communicate through its physical layer (e.g., FOUNDATION Fieldbus) and also through Modbus. Some device manufacturers use Modbus as a complementary common language among their instruments.

Although the Modbus protocol is owned by Modicon, the protocol is available to users and manufacturers under royalty-free license.

HONEYWELL DE3. DE modulates the ___________

on the loop to convey information.

Honeywells DE (Digitally Enhanced) protocol is a digital replacement for standard analog communication protocols (e.g., 420 mA). DE communicates digital information by modulating the current on the loop: a 4 mA signal equals a 1, and a 20 mA signal equals a 0. Because the current itself is modulated, a regular 420 mA analog signal cannot coexist with the DE signal.

The DE protocol is proprietaryit is owned by Honeywell and is not openly available.

1.To communicate control and

monitoring data

2.True

3.Current




ActivitiesFOXBORO FOXCOM4. How does FoxCom operate?The FoxCom protocol operates either as a digital replacement

of a standard analog signal (like Honeywell DE) or as a digital signal overlayed on top of an analog signal (like the HART protocol). In both cases, the digital signal can accomplish the same two-way communication tasks that DE and HART technology can accomplish (e.g., remote transmitter configuration). The all-digital signal conveys information at a relatively speedy 4800 baud. The HART-like signal runs much slower, at 600 baud. (By comparison, the HART protocol operates at 1200 baud.)

When operating in the HART-like mode, FoxCom uses the Bell 202 frequency shift keying method. The communication methods between FoxCom and HART technology are similar enough that most FoxCom-capable devices can communicate using both FoxCom and HART technology. Technicians can even configure many FoxCom-capable devices using a HART communicator.

FoxCom is a proprietary protocolit is owned by Foxboro and is not openly available.

YOKOGAWA BRAIN5. True or False? Frequency shift

keying is a technique used by FoxCom and BRAIN to convey digital information along with the standard analog signal.

Yokogawas BRAIN protocol is based on frequency shift keying, like HART technology. A digital signal is overlayed on top of a standard analog signal (e.g., 420 mA). However, the BRAIN protocol uses non-standard frequency settings to produce digital 1s and 0s.

Yokogawa manufactures a BRAIN communicator that is somewhat like the HART communicator. The BRAIN communicator (like the HART communicator) requires 250 resistance and can be connected anywhere in the loop across a 250 load.

The BRAIN protocol is proprietaryit is owned by Yokogawa and is not openly available.


4.As a digital-only protocol and as a

digital signal overlayed on top of a

standard analog signal

5.True


Activities


Advantages of HART and FieldbusThe HART and FF communication technologies maintain significant advantages over the four other protocols described in this section. A brief comparison can quickly highlight some of the most important advantages.

COMPARING HART WITH FOXCOM AND BRAIN6. What benefits does the HART

protocol have as compared to FoxCom and BRAIN?

HART, FoxCom, and BRAIN use essentially the same frequency shift keying method of overlaying digital information onto an analog signal. All three protocols can be used via a communicator connected anywhere in the control loop.

HART technology has two important benefits that FoxCom and BRAIN do not have. HART technology is:T An open protocolT Widely adopted in the industry

Open Protocol7. Customers view HART

technology as a stepping-stone to __________________ technology.

Both FoxCom and BRAIN are controlled by single vendors, which lock customers into devices manufactured by that vendor. HART technology is an open protocol that is not owned by a single vendor, which frees customers to choose devices from any manufacturer that supports the protocol. HART is supported by over 140 companies, including Foxboro and Yokogawa.

Widely Adopted in the IndustryHART technology is the most widely adopted digital protocol in the process control industry, accounting for the vast majority of all digital device communication. The HART Communication Foundation estimates that over 20 million HART devices are in use today worldwide. Each year, as more plants convert from simple analog communication to a digital strategy, the majority of those plants will choose HART technology as a logical first step.

Customers have overwhelmingly chosen to buy products that use open protocols.

HART is a logical stepping stone to fieldbus technology, because customers can maintain their investment in analog technology.

6.The HART protocol is an open

protocol and it has been widely

adopted in the industry

7.Fieldbus


Advantages of HART and Fieldbus


ActivitiesBecause HART technology is so widely adopted, most device manufacturers build HART-capable instruments, which results in even wider industry adoption. Wide adoption assures customers that their HART devices will interoperate with an enormous number of other devices from many manufacturers.

8. Why is wide industry adoption a benefit to HART technology?

COMPARING HART WITH DE9. True or False? DE forces

customers to abandon their analog systems because DE cannot coexist with an analog signal.

HART technology and DE commonly compete for customers. However, HART technology and DE are not equal competitors. HART technology has significant advantages over DE, including:T Maintained analog signalsT Simultaneous variable transmissionT Broad industry support

Maintained Analog SignalsHART technology overlays its digital signal on top of a standard analog signal. The analog signal is perfectly preserved. DE, on the other hand, replaces the analog signal with a digital signal.

Because DE cannot coexist with an analog signal, customers who adopt DE must throw away their investment in analog technology. Customers who adopt HART technology, however, are free to continue using their analog systems.

Simultaneous Variable TransmissionHART instruments can update up to four process variables with each transmission. DE can only update one variable per transmission. DE sends a secondary variable on the second transmission, a tertiary variable on the third transmission, and so on. This strategy delays transmission of the primary variable by two or three cycles.

The HART protocol is the most widely adopted digital protocol in the process control industry. All proprietary protocols combined are expected to amount to only a tiny fraction of total device sales in the coming years.

8.Continued viability is ensured.

9.True

Activities



Advantages of HART and FieldbusBroad Industry SupportHART technology enjoys broad industry support. Over 200 device manufacturers build HART-capable instruments. DE is restricted to Honeywell instruments and a few licensed products from other vendors.

10. Name three advantages FF has over modbus, DE, FoxCom, and BRAIN.

FOUNDATION FIELDBUS ADDED ADVANTAGESFF is the only communication technology to offer substantial process control advantages such as:T Device interoperabilityDevices from the same and/or

different manufacturers can typically coexist in the same network, but only FF devices communicate with each other by design

T Network flexibilityOnly FF offers true plug-and-play device networks

T Control in the fieldOnly FF is able to offer remote, intelligent devices for which control is located right at the device


10.Device interoperability, network

flexibility, and control in the field

Workbook Exercises


Workbook ExercisesNote: All exercise answers are located at the end of this module.

EXERCISE 8.1THE ROLE OF COMMUNICATION TECHNOLOGY1. Which of the following are roles that communication technology performs? (Select all that apply.)

a) It interprets sensor data and transfers the data to a control room.

b) It rectifies sensor failures from the control room.

c) It enables technicians to remotely configure transmitters.

d) It reports transmitter problems to a control room.

2. How does control in the field change the way the process control industry uses communication technology?

a) Engineers can develop sophisticated control strategies that happen right at the measurement device.

b) Plants can rely much less on central control systems.

c) Providing improved loop integrity reduces the need for redundant controllers and redundant I/Os.

d) Permits multiple devices to exchange process control information simultaneously.

e) Local loops are safermodifying them (or failure of one loop) does not have to affect the rest of the plant network.

Communication TechnologiesFor Internal Use Only 2009 Rosemount Inc.

Workbook Exercises

Workbook ExercisesEXERCISE 8.2COMMUNICATION COMPONENTS1. Match each communication component to its diagrammatic description.

___ Sensor a)

___ Process variable b)

___ Signal processor c)

___ Output signal d)

2. What converts a process variable such as pressure into an electrical signal (for example, millivolts)?

a) Controller

b) Sensor

c) Transmitter

3. Which of these statements explains why an analog-to-digital (A/D) converter and a digital-to-analog (D/A) converter might be necessary for device communication? (Select all that apply.)

a) Transmitters with digital electronics require a digital process value.

b) Dependent devices such as valves and programmable logic controllers (PLCs) can only receive digital signals from transmitters.

c) Transmitters used with integral LCD display require an analog signal.

d) Dependent devices such as valves and programmable logic controllers (PLCs) can only receive analog signals from transmitters.

Workbook Exercises


Workbook ExercisesEXERCISE 8.3ANALOG AND DIGITAL PROTOCOLS1. Indicate whether each of the following is an analog signal or a digital protocol by checking the

appropriate column.

2. Write the letter of each description below its image identifier.

a) Continuously varies

b) Discrete values only

_____________ c) Created by sampling

d) Analog

e) Digital

_____________

3. A customer requires 10 additional transmitters, which will be fairly inaccessible once they are installed. She also indicates that she needs to control costs. Why would you advise this customer to consider digital communication technology? (Select all that apply.)

a) Digital transmitters require less wiring, and there are therefore cheaper to install.

b) Digital transmitters are more accurate, so money will be saved through improved process control.

c) Digital transmitters offer the advantage of self-calibration.

d) Technicians can communicate with digital transmitters remotely.

Analog Signal Digital Protocol

420 mA

HART

FOUNDATION Fieldbus

15 V

315 psi


Workbook Exercises

Workbook ExercisesEXERCISE 8.4HOW HART DEVICES COMMUNICATE1. HART devices use a technique called frequency shift keying. A frequency of _______ equals 1,

and a frequency of _________ equals zero. Because the average modulation on the wire is zero,

the HART signal has ___________ effect on the analog signal.

Answer 1 Answer 2 Answer 3a) 1100 a) 1100 a) No

b) 2200 b) 2200 b) Minimal

c) 31250 c) 31250 c) Major

2. Which of the following descriptions are characteristics of HART communication?

a) It requires a minimum 250 ohms resistance in the loop to establish HART communication.

b) The transmission rate is 2200 bits per second.

c) It requires no loop resistance to establish HART communication.

d) It uses two different frequencies to indicate 1 and 0.

Workbook Exercises


Workbook ExercisesEXERCISE 8.5SIGNAL CONVERSIONNote: Use the diagram below to answer all the questions in this exercise.

1. If the sampling rate changes from 10 samples per second to 20 samples per second, what will happen to the digital process value?

a) It will have twice as many steps.

b) It will decrease by half.

c) It will be unaffected.

d) It will decrease marginally.

2. If the analog signal changes to a flat line, the digital value will also become a flat line that matches (or very nearly matches) the analog signal.

a) True

b) False


Workbook Exercises

Workbook Exercises3. Sampling interval is more important when the process value ____________ changes.

a) Frequently

b) Never

c) Rarely

4. What general statement can you make about data loss in A/D conversions based on the illustration?

a) A/D converters with high sampling rates and sampling precision will not lose any data during the conversion process.

b) A/D converters with high sampling rates and sampling precision can lose some data during the conversion process.

c) A/D converters with low sampling precision lose data during the conversion process.

d) A/D converters with low sampling rates lose data during the conversion process.

Workbook Exercises


Workbook ExercisesEXERCISE 8.6ADVANTAGES OF HART TECHNOLOGY1. A customer is considering the upgrade of 10 analog transmitters to HART transmitters, but he has

expressed concern about the initial investment amount. What reassurances can you provide? (Select all options that apply.)

a) HART transmitters can be used with the existing equipment that uses the 420 mA signaling standard.

b) HART transmitters only deal with digital communication, and since an analog signal is not required, wiring and control system costs are reduced.

c) HART transmitters can be connected in multidropped networks, which can save on wiring and control system costs.

d) There can be unlimited multidropping of HART transmitters in a single loop.

e) HART transmitters run their own self-diagnostics, thereby reducing expensive downtime.

2. Which of the following statements is applicable to HART multidropped networks?

a) Only analog communication is possible.

b) Only digital communication is possible.

c) Both digital and analog communication is possible.


Workbook Exercises

Workbook ExercisesEXERCISE 8.7HART COMMUNICATORS1. Which of these statements are applicable to HART communicators? (Select all that apply.)

a) A technician can configure many transmitters individually through a single connection by using a communicator on a multi-dropped network.

b) Device descriptions allow communicators to be easily upgraded with information about new transmitter functions.

c) Wired transmitters provide access to HART devices from any point in the loop.

d) Communicators allow technicians to access HART devices from any point in the loop across a 250 ohms load.

e) Multiple HART communicators can be used to communicate with multiple HART devices at one time in a multidropped network.

2. HART ___________________ allow technicians to access HART transmitters from anywhere in

the loop across a minimum ________________ ohms load.

Answer 1 Answer 2

a) Sensors a) 125

b) Communicators b) 250

c) Transducers c) 500

3. HART communicators are quick and easy to upgrade with new device descriptions.

a) True

b) False

Workbook Exercises


Workbook ExercisesEXERCISE 8.8FOUNDATION FIELDBUS BASICS1. Match each layer name and description to the layer code as indicated in the diagram below.

___ X a) User layer: Contains function blocks that can be linked together to provide process control features

___ Y b) Physical layer: Defines the hardware connection of the transmitter to the fieldbus network

___ Z c) Communications stack: Handles transmitter communication on the fieldbus network

2. Match each function to the block name.

___ Analog input (AI) a) Identifies the resources that a device can provide to a FOUNDATION Fieldbus network

___ Resource b) Communicates sensor data to other blocks

___ Proportional/integral/derivative (PID) c) Reads and reports digital process values

___ Analog output (AO) d) Converts a digital process value to an analog value

___ Transducer e) Behaves like a thermostat

X

Y

Z


Workbook Exercises

Workbook Exercises3. Match each function to the block name.

___ Signal characterizer a) Could be used to implement the average of a number of input values

___ Input selector b) Totals a flow signal over time

___ Integrator c) Could be used to allow for temperature compensation in an HTG level application

___ Arithmetic d) Makes the signal from a conical tank linear

Workbook Exercises


Workbook ExercisesEXERCISE 8.9ADVANTAGES OF FOUNDATION FIELDBUS1. How does FOUNDATION Fieldbus address the problem of traditional analog wiring costs?

a) Its devices offer complete remote control and require no wiring, leading to a complete reduction of wiring costs.

b) Its devices require far less wiring than analog transmitters, which can lead to substantial cost savings.

c) Its devices can run on the wiring of an existing analog system without terminators and power conditioners.

d) Its technology allows an unlimited number of field devices to be multidropped in a single segment, which can lead to substantial cost savings.

2. FOUNDATION Fieldbus devices are interoperable by design. Any device from any manufacturer can communicate with any other device.

a) True

b) False

3. FOUNDATION Fieldbus devices _______________ the need for large, central control systems

and their attendant network of wires. They can also handle many control responsibilities by

_______________.

Answer 1 Answer 2

a) Support a) Host system

b) Increase b) Themselves

c) Reduce c) Wiring direct

4. FOUNDATION Fieldbus fulfills all the roles of digital communication technology.

a) True

b) False


Workbook Exercises

Workbook Exercises5. A plant manager wants to use 100% FOUNDATION Fieldbus for a new plant expansion, but

intends to wire point-to-point. What would you advise? (Select all that apply).

a) There is little need to resort to point-to-point wiring because FOUNDATION Fieldbus devices can be connected in a number of different network configurations.

b) A point-to-point wiring setup will be appropriate since all the devices have to share the same network.

c) There is no need for point-to-point wiring because the FOUNDATION Fieldbus devices can be controlled remotely.

d) The manager could rewire her devices so they share the same network wires, thereby cutting down wiring and maintenance costs dramatically.

Workbook Exercises


Workbook ExercisesEXERCISE 8.10FOUNDATION FIELDBUS NETWORKS

1. Topology is the shape of the network, and FOUNDATION Fieldbus has a unique network shape.

a) True

b) False

2. How is intrinsic safety observed in a FOUNDATION Fieldbus network? (Select all that apply.)

a) A safety barrier must be placed between the intrinsically safe and non-safe segments.

b) The intrinsically safe and non-safe segments must have separate wiring properties.

c) All devices on the intrinsically safe side must be bus-powered.

d) The number of devices on an I.S. segment is unlimited.

e) The device must be certified as I.S.

3. The link active scheduler (LAS) need not necessarily be in the control room. The LAS can be virtually anywhere on the network.

a) True

b) False


Workbook Exercises

Workbook ExercisesEXERCISE 8.11THREE PROFIBUS VARIANTS1. Write the letter of the descriptive characteristic next to the appropriate Profibus variant.

(Characteristics may be used more than once.)

___ ProfibusFMS a) Distributed I/O protocol

___ ProfibusDP b) Uses high-speed signals

___ ProfibusPA c) Supports intrinsically safe operation

d) Designed to meet factory automation needs

e) Suited for master-to-master communication

f) Designed to meet process automation needs

2. Which of these ProfibusPA items are similar to FOUNDATION Fieldbus? (Select all that apply.)

a) Network management

b) Physical layer

8 communication technologies

Documents

hart communication foundation

basic communication

remote device communication

signal processor

output signal

ma signal

psi signal

fieldbus foundation