2. Distributed Control System and Programmable Logic Control
Course Aim
The aim of this training course is to build up the procedural and
declarative knowledge required to be recognized by projects engineer that
don not have past background of DCS or PLC. This will help them to
supervise projects dealing with control systems with a strong background.
In this course, the training cycle is divided in five steps that necessitate
the cooperation between the instructor and the trainees. These steps are
shown in figure below, they are summarized as follows:
1. Define the knowledge and skills required to be developed.
2. Define the elements of each knowledge or skill.
3. Formulate a verbal phrase for the learning objective of each
element.
4. Choose an adequate instructional activity to present each element.
5. Set up an indicator to measure the outcomes of the course and
modify the training skills to adapt the vocational needs.
Define
Knowledge Determine
& Skills Elements
Measure Learning
& Correction Objectives
Instruction
Activity
Training Cycle.
1
3. Knowledge and Elements
Illustrate DCS & PLC Benefits, Usage and History.
Overview of control system history.
Control system benefits and usage.
Types of control
Develop Knowledge of DCS Components (Hardware & Software).
Infrastructure [Communication Bus, Interfaces, Controllers,
Gateways, RTU, Others].
Hardware and technologies.
Software [Configuration, Graphics, Alarming, Trending, System
Management, Others].
Extend Knowledge of DCS installation and Maintenance.
Site Installation, Commissioning and Startup.
Diagnostics, Spares, Tools and Power Distribution.
Maintenance [Backup, Replacements and System Installation].
Develop Knowledge of PLC Components.
PLC fundamentals.
PLC Logic.
4. Table of Contents
Section I
Chapter 1 Introduction
Chapter 2 Regulatory Control
Section II
Chapter 3 DCS Infrastructure
Chapter 4 DCS Hardware
Chapter 5 DCS Software
Section III
Chapter 6 Installation
Chapter 7 Maintenance
Chapter 8 Power Distribution
Section IV
Chapter 9 PLC Fundamentals.
Chapter 10 Ladder Logic And SFC
Appendices
A Electrical Relay Diagram And P&ID Symbols
B Serial Communication
C Networking
D Software Engineering
6. Distributed Control System and Programmable Logic Control
Chapter 1
Control Systems
1.1 Automation System Structure
Although applications differ widely, there is little difference in the
overall architecture of their control systems. Why the control system of a
power plant is not sold also for automating a brewery depends largely on
small differences (e.g. explosion-proof), on regulations (e.g. Food and
Drug Administration) and also tradition, customer relationship.
The ANSI/ISA standard 95 defines terminology and good practices
Level
4 Business Planning & Logistics Enterprise Resource
Plant Production Scheduling
Operational Management, etc.
Level Manufacturing
3 Operations & Control
Dispatching Production, Detailed Product Manufacturing Execution
Scheduling, Reliability Assurance,...
Level
2,1,0
Batch Continuous Discrete Control & Command
Control Control Control
1.1.1 Large Control System Hierarchy
• Administration: Production goals, planning
• Enterprise: Manages resources, workflow, coordinates activities of
different sites, quality supervision, maintenance, distribution and
planning.
5
7. • Supervision: Supervision of the site, optimization, on-line
operations. Control room, Process Data Base, logging (open loop)
• Group (Area): Control of a well-defined part of the plant. closed
loop, except for intervention of an operator)
o Coordinates individual subgroups
o Adjusting set-points and parameters
o Commands several units as a whole
• Unit (Cell): Control (regulation, monitoring and protection) of a
small part of a group (closed loop except for maintenance).
o Measure: Sampling, scaling, processing, calibration.
o Control: regulation, set-points and parameters
o Command: sequencing, protection and interlocking
• Field: Sensors & Actors, data acquisition, digitalization, data
transmission, no processing except measurement correction and
built-in protection.
4 Planning, Statistics, Finances administration
3 Workflow, Resources, Interactions enterprise
SCADA supervisi on
Supervisory Supervisory
2
And Data
Group Control
Unit Control
1
Field
Sensors T
& Actors A V
0 Primary
Figure 1.1 Large control system hierarchy
8. 1.1.2 Response Time and Hierarchical Level
Planning ERP (Enterprise
Level Resource Planning)
MES
Execution (Manufacturing
Level Execution System)
SCADA
(Supervisory Control
Supervisory and Data Acquisition)
Level
DCS
(Distributed
Control System)
Control
Level PLC
(Programmable
Logic Controller)
ms seconds hours days weeks month years
Figure 1.2 Response Time And Hierarchical Level
1.2 What is DCS?
A DCS is an integrated set of modules with distributed functions.
– Multi-loop controllers (10’s-100’s) that connect to field
devices
– Supervisory coordinating controllers
– Multi-loop operator stations and engineering stations
– Servers for system data management
– Control network for intercommunication
– External connections
9. Supervisory Operator
System Stations
Remote Users Controller
www Server
Engineering
Station
Remote
Server
Control Network
Multi-loop
Controller
Direct I/O Module
Other Industrial Devices
Figure 1.3 DCS Hierarchy
A DCS, throughout the whole system, must provide:
– Performance: control must be faster than the process.
– Determinism: control must always take the same time.
– Fault tolerance: redundancy; must fail to a known state.
– Security: must have access restrictions/controls.
Even though performance, ease of use, and interoperability are key
evaluation criteria for any control system software package, the following
is intended to provide the manufacturing engineer with a concise list of
control system software evaluation criteria.
1. INTEROPERABILITY.
This refers to the interaction of all control system hardware and
software components at all levels.
2. INTERCONNECTIVITY.
This criterion is concerned with the transmission medium, which is
constrained by the network topology and how efficiently the
system’s components communicate with each other.
10. 3. DISASTER PROCESSING.
This component is defined by the efficiency with which the
software provides the operator with system failure information and
the ease at which the operator is permitted to bring the system back
to maximum operation after system failure.
4. DATABASE.
This refers to the software’s ability to maintain the system’s
database.
5. PROCESSES/DATA.
This criterion is concerned with the variety of processes and data
that can be controlled by the SCADA package.
6. DIAGNOSTICS.
The SCADA package’s ability to assist in the resolution of system
failures is evaluated by this diagnostic utility.
7. SECURITY.
This component is concerned with the levels of security provided
by the software.
8. MONITORING/CONTROL
Monitoring of a given process in real-time and control of that
process, within preset parameters, is evaluated by this criteria.
9. ALARM MANAGEMENT/LOGGING.
This is the category for detecting, annunciating, managing, and
storing alarm conditions.
10. STATISTICAL PROCESS CONTROL.
This is the portion of the SCADA package that evaluates the
process data. Production and quality is greatly effected by this data.
12. OPERATOR INTERFACE.
The graphical user interface (GUI) is evaluated using this criterion.
11. 13. TRENDING.
The software’s ability to display trending plots using historical and
current data is considered in this category.
14. REPORT GENERATION.
The production of logs and reports using current real-time data and
data retrieved from historical files is evaluated under this category.
Due to the advancements in computer technology and low cost, a
personal computer-based distributed control system can be installed for a
fraction of the cost required just a few years ago. However, prior to
selecting any piece of DCS equipment, first examine the existing
equipment, in particular the smart controllers, for network compatibility.
Then, examine and select the software to be employed.
1.3 What is PLC?
A programmable logic controller, also called a PLC or
programmable controller, is a computer-type device used to control
equipment in an industrial facility. The kinds of equipment that PLCs can
control are as varied as industrial facilities themselves. Conveyor
systems, food processing machinery, auto assembly lines…you name it
and there’s probably a PLC out there controlling it.
In a traditional industrial control system, all control devices are
wired directly to each other according to how the system is supposed to
operate. In a PLC system, however, the PLC replaces the wiring between
the devices. Thus, instead of being wired directly to each other, all
equipment is wired to the PLC. Then, the control program inside the PLC
provides the “wiring” connection between the devices.
12. The control program is the computer program stored in the PLC’s
memory that tells the PLC what’s supposed to be going on in the system.
The use of a PLC to provide the wiring connections between system
devices is called soft-wiring.
Let's say that a push button is supposed to control the operation of
a motor. In a traditional control system, the push button would be wired
directly to the motor. In a PLC system, however, both the push button and
the motor would be wired to the PLC instead. Then, the PLC's control
program would complete the electrical circuit between the two, allowing
the button to control the motor.
Figure 1.4 PLC development
A PLC basically consists of two elements:
• The central processing unit
• The input/output system
1.3.1 The Central Processing Unit
The central processing unit (CPU) is the part of a programmable
controller that retrieves, decodes, stores, and processes information. It
also executes the control program stored in the PLC’s memory. In
13. essence, the CPU is the “brains” of a programmable controller. It
functions much the same way the CPU of a regular computer does, except
that it uses special instructions and coding to perform its functions. The
CPU has three parts:
• The processor
• The memory system
• The power supply
The processor is the section of the CPU that codes, decodes, and
computes data. The memory system is the section of the CPU that stores
both the control program and data from the equipment connected to the
PLC. The power supply is the section that provides the PLC with the
voltage and current it needs to operate.
Figure 1.5 Microprocessor Hardware
1.3.2 The input/output (I/O) system
It is the section of a PLC to which all of the field devices are
connected. If the CPU can be thought of as the brains of a PLC, then the
I/O system can be thought of as the arms and legs. The I/O system is what
actually physically carries out the control commands from the program
stored in the PLC’s memory.
14. The I/O system consists of two main parts:
• The rack
The rack is an enclosure with slots in it that is connected to the CPU.
• I/O modules
I/O modules are devices with connection terminals to which the field
devices are wired.
Together, the rack and the I/O modules form the interface between the
field devices and the PLC. When set up properly, each I/O module is both
securely wired to its corresponding field devices and securely installed in
a slot in the rack. This creates the physical connection between the field
equipment and the PLC. In some small PLCs, the rack and the I/O
modules come prepackaged as one unit.
Figure 1.6 I/O Racks
15. 1.4 How is a DCS different from a PLC system?
DCS PLC
Mfr sells a complete system of integrated Mfr sells some components; an SI
components. acquires others and engineers the system.
Mfr supports the system. Mfr supports the components.
On-line repair/ maintenance are the norm. Off-line repair/ maintenance are the norm.
System management built-in. System management designed per project.
Users expect to evolve/upgrade/expand a System is a one-off project (like a house).
system over 10/20/30 years. Upgrades / expansions are new projects.
1.5 Redundancy and Fault Tolerance
1.5.1 Redundancy
• Hardware redundancy
– add extra hardware for detection or tolerating faults
• Software redundancy
– add extra software for detection and possibly tolerating faults
1.5.2 Fault Tolerance
• Error Detection
• Damage Confinement
• Error Recovery
• Fault Treatment
1.5.2.1 Error Detection
• Ideal check
– Check should be independent from system
– Check fails if system crashes
16. • Acceptable check
– Cost
– Reasonable check, e.g. monitor rate of change
• diagnostics
– Performed “by system on system components”
– E.g. power-up diagnostics
1.5.2.2 Damage Confinement
• Error might propagate and spread
• Identify boundaries to state beyond which no information exchange
has occurred
1.5.2.3 Error Recovery
• Backward recovery
– State is restored to an earlier state
– Requires checkpoints
– Most frequently used
– Recovery overhead
• Forward recovery
– Try to make state error-free
– Need accurate assessment of damage
– Highly application-dependent
1.5.2.4 Fault Treatment
• If transient fault: restart system, goto error-free state
• System repair
– On-line, no manual intervention, (automatic)
– Dynamic system reconfiguration
– Spare (hot or cold)
17. 1.5.2.5 Fault Coverage
• Measure of system’s ability to perform:
– Fault detection
– Fault location
– Fault containment
– (and/or fault recovery)
• Note:
– Recovery implies that the system as a whole is operational
– This does not imply that a “repair” occurred
– E.g. duplex system with benign fault can recover to continue
operation on one non-faulty processor
1.5.2.6 Hardware Redundancy
• Passive (static)
– Uses fault masking to hide occurrence of fault
– No action from the system is required
– E.g. voting
• Active (dynamic)
– Uses comparison for detection and/or diagnoses
– Remove faulty hardware from system => reconfiguration
• Hybrid
– Combine both approaches
– Masking until diagnostic complete
– Expensive, but better to achieve higher reliability
1.5.2.7 Passive Hardware Redundancy
• N-Modular Redundancy (NMR)
– N independent modules replicate the same function
18. • Parallelism
– Results are voted on requirements: N >= 3
• TMR (Triple Modular Redundancy)
1.5.2.8 Fault tolerant structures
Fault tolerance allows continuing operation in spite of a limited
number of independent failures. Fault tolerance relies on work
redundancy.
1.5.2.9 Static redundancy: 2 out of 3
• Workby of 3 synchronised and identical units.
– All 3 units OK: Correct output.
– 2 units OK: Majority output correct.
– 2 or 3 units failure: Incorrect output.
– Otherwise: Error detection output.
Process input
sync sync
Voter
Process output
Figure 1.7 (2 out of 3) Redundancy
1.5.2.10 Dynamic Redundancy
• Redundancy only activated after an error is detected.
– Primary components (non-redundant)
– Reserve components (redundancy), standby (cold/hot standby)
19. Input
Primary unit Standby unit
Switch
Output
Figure 1.8 Dynamic Redundancy
1.5.2.11 Workby and Standby
Workby Hot standby Cold standby
sync sync
on-line workby on-line standby
=?
Both computers are doing Standby is no operational
Standby is not computing
the same calculations Error detection needed.
Error detection needed.
at the same time Long switchover period
Easy switchover in case
Comparison for easy with loss of state info.
of failure.
error detection. Easy repair of reserve unit. No aging of reserve unit.
Comparator needed. Non-
redundant continuation
in case of failure?
Figure 1.9 Workby and Standby
1.5.2.12 Workby Fault-Tolerance for Integrity and Persistency
input input
synchronization synchronization
Worker Co E Worker Co E
W-orker D W-orker D
Matching Matching
Output Output
comparator commutator
disjunctor
output output
INTEGER PERSISTENT
Figure 1.10 Workby Fault-Tolerance for Integrity and Persistency
20. 1.5.2.13 Hybrid Redundancy
Mixture of workby (static redundancy) and standby (dynamic redundancy).
work- work- work- stand- stand-
by by by by by
voter
Reconfiguration work- work- work- stand-
failed
(self-purging by by by by
redundancy)
voter
Figure 1.11 Hybrid Redundancy
1.6 Microprocessor Control
For simple programming the relay model of the PLC is sufficient.
As more complex functions are used the more complex VonNeuman
model of the PLC must be used. A computer processes one instruction at
a time. Most computers operate this way, although they appear to be
doing many things at once. Consider the computer components shown in
Figure 1.12.
Figure 1.12 Simplified Personal Computer Architecture
21. Input is obtained from the keyboard and mouse, output is sent to the
screen, and the disk and memory are used for both input and output for
storage. (Note: the directions of these arrows are very important to
engineers, always pay attention to indicate where information is flowing.)
This figure can be redrawn as in Figure 1.13 to clarify the role of inputs
and outputs.
Figure 1.13 An Input-Output Oriented Architecture
In this figure the data enters the left side through the inputs. (Note:
most engineering diagrams have inputs on the left and outputs on the
right.) It travels through buffering circuits before it enters the CPU. The
CPU outputs data through other circuits. Memory and disks are used for
storage of data that is not destined for output. If we look at a personal
computer as a controller, it is controlling the user by outputting stimuli on
the screen, and inputting responses from the mouse and the keyboard.
A PLC is also a computer controlling a process. When fully
integrated into an application the analogies become;
• Inputs - the keyboard is analogous to a proximity switch input
circuits - the serial input chip is like a 24Vdc input card
22. • Computer - the 686 CPU is like a PLC CPU unit
• Output circuits - a graphics card is like a triac output card
• Outputs - a monitor is like a light
• Storage - memory in PLCs is similar to memories in personal
computers
It is also possible to implement a PLC using a normal Personal Computer,
although this is not advisable. In the case of a PLC the inputs and outputs
are designed to be more reliable and rugged for harsh production
environments.
1.7 Role Play
Each trainee should act a role play on the following:
1. Automation system structure.
2. What DCS and PLC and their differences?
3. Redundancy and fault tolerance.
23. Chapter 2
Regulatory Control
2.1 Learning Objectives
• Introduce Regulatory Control.
• Understanding PID control.
• Differentiate between various control loops.
2.2 Introduction
Most of the applications of industrial control process used simple
loops which regulated flows, temperatures, pressures and levels.
Occasionally ratio and cascade control loops could be found. There are
many benefits for using regulatory control. One of the most important is
simply closer control of the process. Process control is one part of an
overall control hierarchy that extends downwards to safety controls and
other directly connected process devices, and upward to encompass
process optimization and even higher business levels of control such as
scheduling, inventory management.
Most control engineers would recognize the form of response
shown in figure 2.1. Actually the response could be determined by
solving a differential equation. It is more important to have a good
understanding of the physical response than to be able to predict the
solution by solving the differential equation.
24. Figure 2.1 Response of simple dynamic process to step input change
Instrumentation, control and process engineers abstract the pictorial
form of the process into an iconographic diagram called "Piping and
Instrumentation Diagram", i.e. P&ID. Figure 2.2 is an example of the
P&ID.
Figure 2.2 Control loop representation used on P&IDs.
For description and analysis of a control loop, without referring to
whether it is implemented with analog or digital hardware, a block
diagram as shown in figure 2.3 is beneficial.
Figure 2.3 Simplified block diagram representation of process control loop.
25. 2.3 PID Control
2.3.1 Feedback Control
The principle of feedback is one of the most intuitive concepts
known. An action is taken to correct a less satisfactory situation then the
results of the action are evaluated. If the situation is not corrected then
further action takes place. Feedback control can be classified by the form
of the controller output. One of the simplest forms of output is discrete
form, also called on-off or two position control. An example of this is the
household thermostat, which activates heating unit if the temperature is
below the setting, or deactivates the unit if the temperature is above the
setting.
Figure 2.4 On-Off Control.
The idea of two position control can be extended to multi-position
control; an example is commercial air-conditioning refrigeration
equipment which is operated by loading and unloading compressor
cylinders. The ultimate extension is infinite number of positions which is
called modulating control; an example is the process controller output
that can drive a valve to any position between 0 and 100 percent, as
shown in figure 2.5.
26. Figure 2.5 Flow versus position, infinite position Control.
2.3.2 Modes of Control
Feedback controllers use one, two, or three methods to determine
the controller output. These methods, called the modes of control,
including the following:
• Proportional (P)
• Integral (I)
• Derivative (D)
In general these modes can be used singly or in combination.
2.3.2.1 Proportional Mode
With a controller containing only the proportional mode, the
controller output is proportional to the measurement value only. Neither
history of the measurement value nor consideration to the rate of change
is utilized. Adjustment, i.e. tuning, of the controller is simple because
there is only one adjustment as shown in figure 2.6.
27. Figure 2.6 Relationship between input and output for proportional control.
Figure 2.7 illustrates a proportional control system. The rate of
fluid flow into the tank represents the load. To be in equilibrium, the
outflow must be the same as the inflow. The outflow is achieved by a
particular valve position where the fixed mechanism between the float,
pivot and link attain.
Figure 2.7 Proportional control.
2.3.2.2 Integral Mode
An integrator is the ideal device for automating the procedure for
adjusting the controller output bias. It is called the automatic reset.
2.3.2.3 Derivative Mode
The derivative is used to anticipate the effect of load changes by
adding a component to the controller output that is proportional to the rate
of change of the measurement. See figure 2.8.
28. Figure 2.8 PID control.
2.3.3 Control Loop Structure
For microprocessor control system, control strategy is configured
by a series of software function blocks. Just like a set of hardware
modules require interconnections to form a complete control system, a set
of software function blocks also acquire interconnections, i.e. soft-wiring.
Figure 2.9 shows a simple feedback loop with the software portion
consists of three function blocks:
• An analog input block that causes the analog to digital converter to
convert the incoming 4-20mA signal to an analogous value. The value
is deposited in a memory register.
• A PID control block which obtains the measurement value from the
analog input block and compares it with the setpoint then it executes a
PID algorithm to calculate the output.
• An analog output block that obtains from the PID block the required
valve position value. The value is converted by a digital to analog
converter to 4-20mA signal.
29. Figure 2.9 Control loop hardware/software structure.
2.3.4 Control Loop Tuning
The power of PID control is that by good choice of control
parameters the controller can be adjusted to provide the desired behavior
on a wide variety of process applications. Determining acceptable values
of these parameters is called tuning the controller. A good criterion for
acceptable performance is the "quarter cycle decay" shown in figure 2.10.
Figure 2.10 quarter cycle decay criterion
Most loops are tuned by experimental techniques, i.e. trial and error.
Figures 2.11 and 2.12 give a tuning map for adjusting control parameters.
30. Figure 2.11 Gain and Reset effects.
Figure 2.12 Derivative effects.
2.4 Control Loop Types
2.4.1 Ratio Control
Figure 2.13 shows the P&ID of a process heater in which the fuel
flow is measured and multiplied by the required air-to-fuel ratio; this
results in the required air flow rate, which is introduced as a setpoint of
the feedback controller. The required air-to-fuel ratio is automatically
adjusted as the output of the stack O2 controller.
31. Figure 2.13 ratio Control..
2.4.2 Cascade Control
In figure 2.14 the temperature controller cascades a steam flow
controller. The temperature controller would react to outlet temperature
drop by increasing the setpoint of the steam flow controller, which in turn
would increase the signal to the valve. The flow will quickly respond to
increased demand from the temperature controller and thus reaching the
desired setpoint of the outlet temperature stream.
Figure 2.13 Cascade Control.
2.4.3 Feedforward Control
With feedforward control, the objective is to drive the controlling
device from a measurement of the disturbance that is affecting the
process, rather than from the process variable itself. In figure 2.14, the
32. application was analyzed the variation in process inlet temperature was
the principle of disturbance. Hence, a feedforward controller is used to
drive the fuel flow controller by sensing the inlet temperature.
Figure 2.14 Feedforward Control.
2.4.4 Selector (Override) Control
There are several ways of using selector switches in control
strategies. One way is to select the higher (or lower) of several
measurement signals to pass the process variable to a feedback controller.
For example, the highest of several process temperatures may be selected
automatically to become the controlling temperature as shown in figure
2.15.
Figure 2.15 Override Control.
33. 2.4.5 Split Range Control
Split range control when one process variable such as plant inlet
pressure is used to manage two different output devices such as plant
bypass control valve and flow control loop for fractionation area. The 4-
12 mA signal is used to control the flow control loop. If the plant cannot
handle all incoming feed, the 12-20 mA signal control the plant bypass
valve to direct extra feed to the outside of the plant.
2.5 Role Play
The trainees are required to play roles about:
1. Introducing regulatory control.
2. Introducing modes of control.
3. Intruding control loop types.
35. Distributed Control System and Programmable Logic Control
Chapter 3
DCS Infrastructure
3.1 Learning Objectives
• Introduce system infrastructure interoperability and interconnectivity.
• Illustrate system components of level 2 control.
3.2 Communication Bus
Figure 3.1: Communication Bus
The communication bus, i.e. the Nodebus, interconnects stations
(Control Processors, Application Processors, Application Workstations,
and so forth) in the system to form a process management and control
node. Depending on application requirements, the node can serve as a
single, stand-alone entity, or it can be configured to be part of a more
extensive communications network.
Operating in conjunction with the Nodebus interface electronics in
each station, the Nodebus provides high-speed, redundant, peer-to-peer
communications between the stations.
The high speed, coupled with the redundancy and peer-to-peer
characteristics, provide performance and security superior to that
34
36. Distributed Control System and Programmable Logic Control
provided by communication media used in conventional computer-based
systems. Station interfaces to the Nodebus are also redundant, further
ensuring secure communications between the stations. The Nodebus can
be implemented in a basic, non-extended configuration or it can be
extended through the use of Nodebus Extenders and Dual Nodebus
Interface Extenders.
3.2.1 Nodebus Interface
The Nodebus Interface is a module which allows direct connection
of a personal workstation (PW), with appropriate Nodebus connector card
and software, to the Nodebus figure 3.2. In this configuration, the PW
functions as a station on the node. The Nodebus Interface allows
connection of a station application workstation hosting an Ethernet
configuration to Nodebus. See figure 3.2.
Figure 3.2 Nodebus Interface Implementation (Typical)
35
37. Distributed Control System and Programmable Logic Control
An Attachment Unit Interface (AUI) cable, connects the PW or an
Ethernet hub configuration to the Nodebus via a Nodebus Interface. A
coaxial cable (ThinNet) connects an Ethernet daisy chain configuration to
the Nodebus via a Nodebus Extender. The Nodebus Interface is non-
redundant, and can be used in any of the Nodebus configurations
described.
3.2.2 Dual Nodebus Interface
The Dual Nodebus Interface (DNBI) is a module which allows
direct connection of stations to the appropriate Nodebus. Connection
between the DNBI and station is made via an AUI cable.
For data transmission security, a separate (RS-423) control cable
connects between the station and the DNBI to allow switching between
the two redundant Nodebus cables. Switching of the Nodebus cables is
controlled by the station, which transmits commands to the DNBI via the
control cable. Figure 3.3 shows connection of a station to the Nodebus
using a DNBI.
Figure 3.3 Local Connection of Station
3.2.3 Dual Nodebus Interface Extender
The Dual Nodebus Interface Extender (DNBX) is functionally
similar to the DNBI, but provides a greater cabling distance. The
36
38. Distributed Control System and Programmable Logic Control
principal transmission medium used is a coaxial Ethernet cable directly
connected to the station end by a standard Ethernet transceiver. Figure 3.4
remote connection of a station to the Nodebus using a DNBX.
Figure 3.4 Remote Connection of Station
3.3 Control Processor
The Control Processor performs regulatory, logic, timing, and
sequential control together with connected:
• Fieldbus Modules (FBMs)
• Fieldbus Cluster I/O Cards (FBCs)
It also performs data acquisition (via the Fieldbus Modules), alarm
detection and notification, and may optionally serve as an interface for
one or more Panel Display Stations.
The non-fault-tolerant version of the Control Processor is a single-width
processor module. The fault-tolerant version consists of two single-width
processor modules.
3.3.1 Enhanced Reliability
The Control Processor offers optional fault- tolerance for enhanced
reliability. The fault-tolerant control processor configuration consists of
two parallel-operating modules with two separate connections to the
Nodebus and to the Fieldbus.
37
37
39. Distributed Control System and Programmable Logic Control
The two control processor modules, married together as a fault-
tolerant pair, are designed to provide continued operation of the unit in
the event of virtually any hardware failure occurring within one module
of the pair. Both modules receive and process information
simultaneously, and the modules themselves detect faults. One of the
significant methods of fault detection is comparison of communication
messages at the module external interfaces. Upon detection of a fault,
self-diagnostics are run by both modules to determine which module is
defective. The non-defective module then assumes control without
affecting normal system operations.
To further ensure reliable communications, the fault-tolerant
control processor performs error detection and address verification tests
in its Nodebus and Fieldbus interfaces. For enhanced reliability during
maintenance operations, the Control Processor is equipped with a
recessed reset button. This feature provides for manually forcing a
module power off and on (reboot) without removing the module from the
enclosure.
3.3.2 Diagnostics
The Control Processor uses three types of diagnostic tests to detect
and/or isolate faults:
• Power-up self-checks
• Run-time and watchdog timer checks
• Off-line diagnostics
Power-up self-checks are self-initiated when power is applied to
the control processor. These checks perform sequential tests on the
various control processor functional elements. Red and green indicators at
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40. Distributed Control System and Programmable Logic Control
the front of the control processor module reflect the successful (or non-
successful) completion of the various phases of the control processor
startup sequence.
The run-time and watchdog timer checks provide continuous
monitoring of control processor functions during normal system
operations. The operator is informed of a malfunction by means of
printed or displayed system messages.
Off-line diagnostics are temporarily loaded into the system for the
purpose of performing comprehensive tests and checks on various system
stations and devices. Using the off-line diagnostics, a suspected fault in
the control processor can be isolated and/or confirmed.
3.4 Engineering Interface
The engineering interface, i.e. Application Processor, is
microprocessor-based application processor/file server stations. They
perform two basic functions:
• As application processor (computer) stations, they perform
computation intensive functions.
• As file server stations, they process file requests from tasks within
themselves or from other stations. Bulk storage devices used with
the Application Processors include floppy disk drives, hard disk
drives, streaming tape drives, and CD-ROMs.
The Application Processors operate in concert with other system
stations (such as communication processors, workstation processors, and
control processors), which provide the necessary means for data
input/output and operator interfacing. A smaller system can utilize a
single Application Processor, while a larger system can incorporate
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41. Distributed Control System and Programmable Logic Control
several Application Processors, each configured to perform specific
functions. Some functions can be performed by individual Application
Processors, while others can be shared by two or more Application
Processors in the same network.
For all models of the Application Processor, applications range
from minimal functions, such as the storage of memory images, alarm
events, and historical data, to larger-scale applications such as database
management and program development.
3.4.1 Application Processor Functions
The following sections describe the major functions performed by
the Application Processors.
3.4.1.1 System and Network Management Functions
The Application Processors perform system management
functions, which include collecting system performance statistics, data
reconciliation, performing station reloads, providing message
broadcasting, handling all station alarms and messages, and maintaining
consistent time and date in all system stations. The Application Processor
also performs network management functions, which comprise that
portion of system management functions which deal with the network.
3.4.1.2 Database Management
Database management involves the storage, manipulation, and
retrieval of files containing data received and/or produced by the system.
The Application Processors utilize the industry-standard Relational Data
Base Management System.
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42. Distributed Control System and Programmable Logic Control
3.4.1.3 File Requests
Each Application Processor contains a file manager, which
manages all file requests associated with bulk memory attached to the
Application Processor. Each Application Processor also supports a
remote file system that allows tasks in one station to share files in
another.
3.4.1.4 Historical Data
The Application Processors can be configured to contain the
Historian function, which maintains a history of application messages and
continuous and discrete I/O values. These values may represent any
parameters such as measurements, setpoints, outputs, and status switches
from stations that have been configured to collect data and send it to a
Historian. In addition, the Historian computes and stores a history of
averages, maximums, minimums, and other derived values. This
information is maintained for display, reporting, and access by
application programs. An archiving facility saves the data on removable
media, where applicable.
The Application Processors can be configured to maintain a history
of errors, alarm conditions, and selected operator actions. The occurrence
of errors, alarms, and events in other stations can be stored (for later
review and analysis) by sending a message defining the event to the
Historian in one or more Application Processors.
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43. Distributed Control System and Programmable Logic Control
3.4.1.5 Graphic Display Support
The Application Processor supports graphic displays by storing and
retrieving display formats, by providing access to objects stored on the
Application Processor, and by storing tasks which execute in a
workstation processor. Application Processors not only provide storage of
information and file management for displays, but also execute programs
that perform display and trend service.
3.4.1.6 Production Control Software
Production control software represents a large range of packages
that require varied Application Processor resources. The following is a
list of packages provided:
• DBMS
• Historian
• Spreadsheet
• Physical Properties Library
• Mathematics Library
• BATCH
The operation and performance of the production control software are
determined by the particular Application Processor configuration.
3.4.1.7 Configuration
Configuration refers to the process of entering or selecting
parameters to define what a software package does, or to define the
environment for a software package. The Application Processors support
configuration functions by providing bulk storage for configuration
parameters and by executing some of the configuration processes.
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44. Distributed Control System and Programmable Logic Control
3.4.1.8 Application Development Facilities
Application development tools are provided to build programs for
all system stations. These include tools to document, enter, translate, link,
test, and maintain programs written in several programming languages.
The Application Processor supports program development for all stations
(workstation processors, control processors, and so forth).
Assembly language, FORTRAN, and C programs can be written on
the Application Processor using standard operating system tools. An
optional package is available including text editors, debuggers, linkers,
revision control, and compilers, plus execution statistics functions.
3.4.1.9 User Application Program Execution
The Application Processors also execute user application programs.
These may be application packages such as special optimizations, test
data collections, special data reductions, or other packages that you may
have already developed. The allocation of resources reserved for user
application varies with each Application Processor.
3.4.2 Diagnostics
The Application Processors utilize three types of diagnostic tests to
detect and/or isolate faults:
• Power-up self-checks
• Run-time and watchdog timer checks
• Off-line diagnostics
Power-up self-checks are initiated when power is applied to the
Application Processor. These checks perform sequential tests on the
43
45. Distributed Control System and Programmable Logic Control
various Application Processor functional elements. Any malfunction
detected during the power-up self-checks is reported by means of
messages printed or displayed on a directly connected printer or terminal.
The run-time and watchdog timer checks provide continuous
monitoring of Application Processor functions during normal system
operations. For any processor model, you are informed of a malfunction
by means of printed or displayed system messages. Off-line diagnostics
are temporarily loaded into the system for the purpose of performing
comprehensive tests and checks on various system stations and devices.
Using the off-line diagnostics, a suspected fault in the Application
Processor can be isolated and/or confirmed.
3.4.3 Workstation Components
The workstation components provide user interface to all System
CRT display functions. A selection of workstation components is
available for command and data entry, along with CRT pointer
manipulation and control. These components interact with software
resident in versions of the system Workstation Processors (WPs) and
Application Workstation Processors (AWs). Many of these components
(displays and keyboards) are "common" and allow interchangeability and
simplicity in mixed technology configurations.
Workstation components include:
• Alphanumeric Keyboard
• Annunciator and Annunciator/Numeric Keyboards
• Workstation Display (with/without Touchscreen)
• Mouse
• Trackball
• Industrial Pointing Device
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46. Distributed Control System and Programmable Logic Control
• Workstation Processor or Application Workstation Processor
• Personal Workstation
• Modular Industrial Console
Selection of the touch screen, mouse, trackball or industrial
pointing device is required for picking display objects on the CRT. The
touch screen has sufficient resolution for all functions normally
associated with a process operator. Only the mouse or trackball provides
the picking resolution necessary for engineer-related functions (for
example, building graphic displays). The touch screen associated with
Workstation Display and the annunciator type keyboards connects to a
Graphics Controller Input Output (GCIO) interface unit located beneath
the workstation display. The GCIO interfaces to the Workstation
Processor and/or Application Workstation that provide secure, high-
speed, bidirectional data flow. The alphanumeric keyboard and trackball
connect together in a functional grouping via a serial communications
link to the processors. Personal Workstations (PW) utilize separate serial
communication links for alphanumeric keyboard and mouse/trackball.
These buses allow a variety of component connections.
Figure 3.5 Table- Workstation Components.
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47. Distributed Control System and Programmable Logic Control
3.4.3.1 Alphanumeric Keyboard
The alphanumeric keyboard is used any time text is entered into the
system. It consists of the full set of alphanumeric keys plus punctuation
and special symbol keys laid out in the standard format, and a numeric
data entry pad (with cursor control).
Figure 3.6 Alphanumeric Keyboard
3.4.3.2 Annunciator Keyboard
The Annunciator Keyboard Figure 3.7 is an array of LED/switch
pairs. It also contains a horn silence switch and a lamp-test switch. Each
LED, under control of the processor software, may be ON, OFF, or
FLASHING as determined by the process conditions. The LEDs, when
used in conjunction with the unit's audible annunciator, form an effective
means of calling a user's attention to specific areas of the system. The
switch associated with each LED can be used to invoke any pre-
configured displays or operator responses..
Figure 3.7 Annunciator Keyboard
3.4.3.3 Workstation Display with/without Touchscreen
The workstation display is an analog cathode ray tube (CRT) color
monitor supporting ultra-high resolution applications. The monitor is
suitable for mounting onto a Modular Industrial Workstation or on a
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48. Distributed Control System and Programmable Logic Control
desktop. The monitor can include a touchscreen optional feature. Figure
3.8 shows the monitor with a tilt and swivel base mounted on the GCIO
interface unit. The GCIO interface supports the touchscreen, annunciator
and annunciator/ numeric keyboard, and audible horn options.
Figure 3.8 Table-Top Workstation Display
The optional touch screen is bonded to the front surface of the CRT
monitor. The user selects display objects by touching them on the screen.
The touch screen senses the action and sends a data signal to the
workstation processor's software indicating the position of the selection.
3.4.3.4 Trackball
The trackball is a stationary component that contains a rotatable
sphere. The trackball can be located on a table top. Rotation of the sphere
causes CRT pointer movement analogous to the mouse action. Buttons
are also provided for user selections/manipulations. See Figure 3.9
Figure 3.9 Trackball
3.4.3.5 Modular Industrial Console
Modular Industrial Consoles provide flexible mounting
arrangements of components. They allow users to configure centralized
or distributed control centers tailored to the functional requirements of
each interaction point in the plant. The modular console furniture
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49. Distributed Control System and Programmable Logic Control
described herein may incorporate a mix of equipment - console displays,
input devices, processors, Fieldbus Modules, data storage devices, and so
on. Alternately, only display-specific equipment can be incorporated.
Modular Industrial Consoles (MICs) are ideal for supporting powerful
multiple-screen, real-time display software interactions. This combination
allows console resources to be optimally allocated to meet changing day-
to-day needs.
3.5 Operator Interface
Operating in conjunction with human interface input/output
components, the workstation processors serve as a link between the
operator and other distributed processor modules. They receive graphic
and textual information both stored internally or from application
processors and generate signals to display the information on a
workstation display. Display formats and data files are available from
bulk storage. Live display information (distributed data objects) is
available from any control -processor, or from shared system global data.
The video information displayed can include free form combinations of
text, graphic illustrations, charts, and control displays.
The workstation processors display textual information as 80 text
characters per line, with four fonts. The processors provide resizable and
restackable windows. Displays for all of the workstation processors may
also be developed using the system software running in a compatible
personal computer.
A workstation processor, together with its workstation monitor and input
components, can be configured with combinations of peripherals to suit
functions and user preferences.
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50. Distributed Control System and Programmable Logic Control
3.6 Gateways
The architecture of the DCS permits it to be connected to other
foreign systems using a gateway module for adapting different
communication protocols. See figure 3.10.
Figure 3.10 Field Automation Subsystem
3.7 Role Play
Each trainee should introduce one of the main components:
1. Communication Bus
2. Control Processor.
3. Application Processor
4. Operator Interfaces and Gateways
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51. Distributed Control System and Programmable Logic Control
Chapter 4
DCS Hardware
4.1 Learning Objectives
• Define fieldbus communication.
• Illustrate system components of level 1 control.
• Demonstrate interconnection between different components.
• Develop knowledge base of foundation fieldbus technology.
4.2 Fieldbus Modules
Fieldbus Modules provide connection of digital I/O, analog I/O,
and Intelligent Transmitters to control processors. There are two types of
Fieldbus Modules: Main and Expansion. Some main modules can be
expanded using an expansion module.
A wide range of Fieldbus Modules is available to perform the
signal conversion necessary to interface the control processor with field
sensors and actuators.
4.3 Fieldbus Interconnection
The Control Processor is used in three different configurations, which
provide broad flexibility in Fieldbus implementation:
• Local Fieldbus (Figure 4.1) - Used only within the enclosure.
Fieldbus Modules attach directly to the redundant local bus.
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52. Distributed Control System and Programmable Logic Control
Figure 4.1 Local Fieldbus
• Twinaxial (Dual-Conductor Coaxial) Fieldbus Extension (Figure
4.2) - Using twinaxial cable, the Fieldbus can optionally extend
outside of the enclosure. Fieldbus Modules attach to the extended
bus through Fieldbus isolators. The twinaxial Fieldbus extension
may be redundant.
Figure 4.2 Twinaxial Fieldbus Extension
• Fiber Optic Fieldbus Extension (Figure 4.3) - The fiber optic
Fieldbus can optionally extend the distance as well as add
application versatility and security.
Figure 4.3 Fiber Optic Fieldbus Extension
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53. Distributed Control System and Programmable Logic Control
All three Fieldbus configurations use serial data communication
complying with Electronic Industrial Association (EIA) Standard RS-485.
4.4 Cluster I/O Subsystem Interfacing
The Control Processor interfaces with the Fieldbus Cluster
Input/Output Subsystem that consists of the Fieldbus, a multi-slot chassis
configuration of a Fieldbus Processor, analog/digital Fieldbus Cards
(FBCs), and power supply and power monitor card. These Cluster I/O
subsystems meet the needs of applications where a high number of
channels per card are required. Figure 4.4 shows a typical twinaxial
Fieldbus configuration.
Figure 4.4 Twinaxial Fieldbus Cluster I/O Subsystem Interface Configuration
4.5 Fieldbus Cluster I/O Subsystem
The Fieldbus Cluster Input/Output Subsystem provides full support
for analog measurement, digital sensing, and analog or discrete control
capabilities. The Subsystem integrates with the Control Processor or
Personal Workstation via the Fieldbus, and includes a multi-slot chassis
configuration made up of a Fieldbus Processor, Analog/Digital Fieldbus
Cards (FBC), subsystem main power supply, and power monitor card.
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54. Distributed Control System and Programmable Logic Control
The Fieldbus Cluster I/O Subsystem is configurable, gathering
analog measurements, while simultaneously handling analog and digital
input and output channels. The Fieldbus Cluster I/O Subsystem is offered
in both non-redundant and redundant configurations. Each in a redundant
pair is individually addressable on the Fieldbus with a unique logical
address. In a redundant configuration, the FBPs provide switchover from
the primary FBP to the redundant FBP and back again automatically. The
FBCs are suitable in applications where a high number of channels per
card are required. They are ideal for non-isolated and isolated input signal
gathering and data acquisition systems where high quantities of "points
per cluster" areas are desired. The FBCs may be optionally connected as
redundant pairs. Various input cards are available with one of the
following three levels of isolation:
• Non-isolated - Each channel is referenced to ground and the card
itself is referenced to ground.
• Group-isolated - Electrically separate card-to-card but not channel-
to-channel on the same card.
• Isolated - Each channel is electrically separated from any other
channel, card, group, building, site, etc.
4.6 Fieldbus Processor
The Fieldbus Processor (FBP) module provides communication
between the Fieldbus Cards (FBCs) and the Control Processor. Optionally
available is redundancy for the FBP module. Each FBP module is
individually addressable via the Fieldbus. If the primary FBP fails or is
taken off-line, the secondary FBP automatically assumes control. It
remains in control until the primary FBP returns on-line (figure 4.5).
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55. Distributed Control System and Programmable Logic Control
Figure 4.5 FBP Overview
4.7 Fieldbus Cards
The Fieldbus Cards support a variety of analog and digital I/O
signals. The FBCs convert electrical I/O signals used by field devices to
permit communication with these devices via the Fieldbus.
The FBCs can be connected in a redundant configuration via the
hardware. The redundant FBCs must be in adjacent slots and they are
connected via a hardware adapter at the interface to the field devices. In
an FBC redundant configuration, the FBP determines which FBC of the
redundant pair is to supply the data to the Control Processor. This is done
in the software by a predetermined set of conditions.
4.7.1 Analog FBCS
The analog FBCs support analog signal types and control functions
equipped with accurate signal conditioning circuitry, the analog cards
interface between process sensors and actuators.
To input an analog voltage (into DCS) the continuous voltage value
must be sampled and then converted to a numerical value by an A/D
54
56. converter. Figure 4.6 shows a continuous voltage changing over time.
There are three samples shown on the figure. The process of sampling the
data is not instantaneous, so each sample has a start and stop time. The
time required to acquire the sample is called the sampling time. A/D
converters can only acquire a limited number of samples per second. The
time between samples is called the sampling period T, and the inverse of
the sampling period is the sampling frequency (also called sampling rate).
The sampling time is often much smaller than the sampling period.
Figure 4.6 Sampling an analog voltage
Analog outputs are much simpler than analog inputs. To set an
analog output an integer is converted to a voltage. This process is very
fast, and does not experience the timing problems with analog inputs.
But, analog outputs are subject to quantization errors. Figure 4.7 gives a
summary of the important relationships. These relationships are almost
identical to those of the A/D converter. Assume we are using an 8 bit D/A
converter that outputs values between 0V and 10V. We have a resolution
of 256, where 0 results in an output of 0V and 255 results in 10V. The
quantization error will be 20mV. If we want to output a voltage of
6.234V, we would specify an output integer of 159, this would result in
an output voltage of 6.235V. The quantization error would be 6.235V-
6.234V=0.001V. The current output from a D/A converter is normally
limited to a small value, typically less than 20mA.
57. Figure 4.7 D/A converter
4.7.2 Digital FBCS
The digital FBCs consist of 32- and 64-channel types. Inputs can
be either voltage monitoring or contact sensing.
Contact inputs must convert a variety of logic levels to the 5Vdc
logic levels used on the data bus. This can be done with circuits similar to
figure 4.8. Basically the circuits condition the input to drive an
optocoupler. This electrically isolates the external electrical circuitry from
the internal circuitry. Other circuit components are used to guard against
excess or reversed voltage polarity.
Figure 4.8 Contact input circuitry.
Contact outputs must convert the 5Vdc logic levels on the DCS
data bus to external voltage levels. This can be done with circuits similar
to figure 4.9. Basically the circuits use an optocoupler to switch external
circuitry. This electrically isolates the external electrical circuitry from
58. the internal circuitry. Other circuit components are used to guard against
excess or reversed voltage polarity.
Figure 4.9 Contact output circuitry.
4.8 Other Modules
• 0 to 20 mA Input/Output Interface
• Pulse Input, 0 to 20 mA Output Interface
• Thermocouple/ Millivolt Input Interface
• RTD Input Interface
• High Power Contact/dc Input/Output Interface
4.9 Foundation Fieldbus Technology
FOUNDATION fieldbus is an all-digital, serial, two-way
communications system that serves as the base-level network in a plant or
factory automation environment.
Figure 4.10 Foundation Fieldbus Network
59. Figure 4.11 Historical development of field devices technology.
It's ideal for applications using basic and advanced regulatory
control, and for much of the discrete control associated with those
functions. Two related implementations of FOUNDATION fieldbus have
been introduced to meet different needs within the process automation
environment. These two implementations use different physical media
and communication speeds.
• H1 works at 31.25 Kbit/sec and generally connects to field devices.
It provides communication and power over standard twisted-pair
wiring. H1 is currently the most common implementation and is
therefore the focus of these courses.
• HSE (High-speed Ethernet) works at 100 Mbit/sec and generally
connects input/output subsystems, host systems, linking devices,
gateways, and field devices using standard Ethernet cabling. It
doesn't currently provide power over the cable, although work is
under way to address this.
Figure 4.12 Field Device Capacity.
60. Conventional analog and discrete field instruments use point-to-
point wiring: one wire pair per device. They're also limited to carrying
only one piece of information -- usually a process variable or control
output -- over those wires. As a digital bus, FOUNDATION fieldbus
doesn't have those limitations.
• Multidrop wiring. FOUNDATION fieldbus will support up to 32
devices on a single pair of wires (called a segment) -- more if
repeaters are used. In actual practice, considerations such as power,
process modularity, and loop execution speed make 4 to 16 devices
per H1 segment more typical.
That means if you have 1000 devices -- which would require 1000 wire
pairs with traditional technology -- you only need 60 to 250 wire pairs
with FOUNDATION fieldbus. That's a lot of savings in wiring (and
wiring installation).
Figure 4.12 Fieldbus wiring diagram.
61. • Multivariable instruments. That same wire pair can handle
multiple variables from one field device. For example, one
temperature transmitter might communicate inputs from as many as
eight sensors -- reducing both wiring and instrument costs.
Other benefits of reducing several devices to one can include fewer pipe
penetrations and lower engineering costs.
• Two-way communication. In addition, the information flow can
now be two-way. A valve controller can accept a control output
from a host system or other source and send back the actual valve
position for more precise control. In an analog world, that would
take another pair of wires.
• New types of information. Traditional analog and discrete devices
have no way to tell you if they're operating correctly, or if the
process information they're sending is valid.
But FOUNDATION fieldbus devices can tell you if they're operating
correctly, and if the information they're sending is good, bad, or
uncertain. This eliminates the need for most routine checks -- and helps
you detect failure conditions before they cause a major process problem.
• Control in the field. FOUNDATION fieldbus also offers the
option of executing some or all control algorithms in field devices
rather than a central host system. Depending on the application,
control in the field may provide lower costs and better performance
-- while enabling automatic control to continue even if there's a
host-related failure.
62. FOUNDATION fieldbus is covered by standards from three major
organizations:
• ANSI/ISA 50.02
• IEC 61158
• CENELEC EN50170:1996/A1
The technology is managed by the independent, not-for-profit
Fieldbus Foundation, whose 150+ member companies include users as
well as all major process automation suppliers around the globe.
Some suppliers have even donated fieldbus-related patents to the Fieldbus
Foundation to encourage wider use of the technology by all Foundation
members.
Interoperability simply means that FOUNDATION fieldbus
devices and host systems can work together while giving you the full
functionality of each component.
4.10 Role Play
Each trainee should introduce one of the main components:
5. Fieldbus Module and Interconnection
6. Fieldbus Processor and Clusters.
7. Foundation Fieldbus technology
63. Chapter 5
DCS Software
5.1 Learning objectives
• To be familiar with main software components of DCS.
• Understand main tasks for each application.
5.2 Standard Application Packages
5.2.1 System Management
Features include:
• Display of equipment information for the station and its associated
input/output devices, buses, and printers.
• Capability for change actions directed to the associated equipment.
• Processing of station alarm conditions and messages.
5.2.2 Database Management
Features include:
• Storage, retrieval, and manipulation of system data files.
• A run-time license for the embedded use of the Relational Database
Management System.
• A spreadsheet package.
5.2.3 Historian
Features include:
• Maintenance of a history of values for process-related
measurements that have been configured for retention by the
Historian.
64. • Maintenance of a history of application messages that have been
sent to the Historian.
• Maintenance of a history of alarms and error conditions which
generate messages for the Historian.
• Access to all Historian data by display and report application
programs.
5.2.4 View Display Manager
Features include:
• Presentation of the operating environment.
• Setting of the overall operating environment according to the type
of user. Process engineers, process operators, and software
engineers have access to specialized functions and databases suited
to their specific requirements and authorizations.
• Dynamic and interactive process graphics.
• Display and processing of current process alarms.
• Group and default displays for control blocks.
• Execution of embedded trending within displays.
5.2.5 Draw Display Builder
Features include:
• Graphical display configuration for viewing and control of process
operation.
• Access to graphical object palettes allowing easy inclusion of
pumps, tanks, valves, ISA symbols, and similar complex objects.
• Ready modification of existing displays using a mouse pointer,
menu items, and quick-access toolbars.
• Association of process variables with objects in the displays.
65. • Dynamic variation of object attributes such as fill level, color,
position, size and visibility with changes in the associated process
variable.
• Inclusion of operator control elements such as pushbuttons and
sliders into displays.
• A library of faceplates which may be configured by simply
specifying the compound and block name of the block to which the
faceplate is to be connected.
5.3 Alarm System
Figure 5.1 Alarm manger
Alarm Manager provides an easy-to-use graphical interface of
preconfigured alarm displays for viewing and quickly responding to
process alarm conditions. The alarm display windows present alarm
messages initiated by the control blocks and related to digital input, state
change, absolute analog, deviation, rate of change, device status
mismatch, and other alarm conditions.
Accessible from any environment, the Alarm Manager Display windows
provide:
66. • Quick, easy access to the most recent alarm messages via the Most
Recent Alarm display or Current Alarm display
• Alarm status and value information dynamically updated from the
control station
• Color-coded priority and status indicators that allow you to quickly
focus in on critical alarms
• Summary displays for different views of the alarm database based
on alarm status
• An historical list of alarms
• The capability to view subsets of alarms based on specific user-
defined criteria
• The capability to silence or temporarily mute workstation and
annunciator horns.
• Secured access to alarming functions dependent on user or system
responsibility
This set of resizable alarm displays providing a variety of current and
historic views of the process alarm database includes:
• A multi-page list of all the current alarms
• A single page of the most recent, active, unacknowledged alarms
with dynamically updating value and status fields
• Three summary displays specific to alarm status also with updating
values and statuses:
o all active, unacknowledged alarms
o all unacknowledged alarms that have returned to normal
o all active, acknowledged alarms
• A list of historized alarms related to the selected historian database
• An operations display for silencing horns, temporarily muting
horns, changing environments
67. These displays allow you to respond to alarm conditions, filter and
analyze specific alarm data, and maintain alarm message files for
reporting purposes.
The Process or Alarm button in the Display Manager (DM) window
indicates the presence of alarms (both acknowledged and
unacknowledged) and provides access to Alarm Manager Displays.
Initially, the Current Alarm Display (CAD) appears and the other
displays are easily accessible from the CAD via its default Displays
menu:
• Most Recent Alarm display (MRA)
• New Alarm display (NEWALM)
• Unacknowledged Alarms display (UNACK)
• Acknowledged Alarms display (ACKALM)
• Alarm History display (AHD)
• Operations display (OPR)
These easy-to-use displays support the following features:
• A pre-configured number of alarms per screen or page
• Pre-configured alarm message information and formatting per
alarm type
• A status area for indication of current Alarm Manager and display
status, such as horns muted, match active, display paused, initial
call-up time
• Buttons for responding to alarm conditions, such as acknowledging
or clearing alarms, and for accessing additional alarm information
and process displays
• Pull-down menus for editing, viewing, and filing functions
• A pull-down menu for accessing other displays
• Pop-up menus for quick access to commonly used functions
68. • A scroll bar and Go To Page option for moving easily through the
alarm list
Although a preconfigured set of alarm displays is provided, many aspects
of the displays and alarm message content are user configurable to
accommodate different process control applications and operational
needs. See the section on Alarm/Display Manager Configurator.
5.4 Historian
The Historian collects, stores, processes, and archives process data
from the control system to provide data for trends, Statistical Process
Control (SPC) charts, logs, reports, spreadsheets, and application
programs. The Historian software is an easy-to-use data collection tool
that allows the user to organize and enforce a plant data collection
philosophy. The Historian provides extensive data collection and
management functions, and data display functions for use by process
engineers or operators.
Typical historical data are process analog and/or digital variables
(points). The Historian can also collect and display application generated
messages. You can use the Historian to collect data in support of the
following production control functions:
• Cost accounting
• Equipment performance analysis
• Historical trending
• Information retrieval
• Inventory management
• Legal record maintenance
• Lost time analysis
69. • Maintenance reporting
• Material accounting
• Process analysis
• Production reporting
• Quality control
The Historian can:
• Retrieve variables from process databases or accept data from
production control databases maintained by user application
programs.
• Perform built-in calculations on the collected data.
• Store calculated (reduced) data in a real time, relational database.
Application software in a plant-wide control system can access the
Historian database to obtain historical data for process control, production
control, and management information reporting.
You can use SPC chart displays of Historian data to monitor process
variables on-line via the Statistical Process Control Package (SPCP).
You can build displays for trending historical data via the Display Builder
and Display Configurator with Trending software.
Using the Report Writer, you can generate detailed reports of historical
data for management information.
Examples of Industrial Software that interface with the Historian are:
• Batch Plant Management
• Data Validator
• Display Manager
• Display Configurator with Trending
• Object Manager (for process data histories)
• Operator Action Journal
• Operator Message Interface
• Real-Time Data Base Manager
70. • Spreadsheet
• Statistical Process Control Package
• System Monitor
• Report Writer
5.5 Draw
Figure 5.2 Draw
Draw is a display builder and configurator that allow you to create
and maintain dynamically updating process displays. Displays can
represent the plant, a process area or a detailed portion of the process.
You can draw basic objects using Draw's toolbars, menu items and
shortcut keys. You assign graphic attributes such as color and line style to
the objects, and then configure them to reflect process variable changes or
operator actions. Draw includes numerous palettes of objects such as
operator buttons, pumps, tanks, pipes, motors, valves and ISA symbols.
You can also create your own palettes for storing complex objects and
company-standard symbols. Displays can include faceplates, trends and
bitmapped images. You can easily edit your displays to reflect changes in
the process control scheme or to maximize operating efficiency and
security.
71. 5.5.1 Configuration
There are two ways of configuring a display object. You can:
1. Choose the Dynamic Update tab to connect one of the object's
attributes, such as visibility or fill level, to a process variable or a
file. With this type of configuration, changes in an attribute are
triggered dynamically by changes in the process variable. No
operator intervention is necessary.
2. Choose the Operator Action tab to connect the entire object to an
action, such as opening a display or executing a command. An
operator triggers the action by selecting the object.
An individual object can have both types of connections, although it can
have only one operator action.
5.5.2 Operator Actions
In a display configured for operator action, an operator can trigger
events by selecting an object (typically a button), moving a slider, or
typing text or a numeric value. In response to an operator action,
variables can be modified, a new display can open or an overlay can
appear.
While you can configure only one operator action for each display
object, you can trigger two or more events with a single operator action
by configuring an object with a View display command script.
Operator Actions include:
• Open Display
• Open Overlay
• Close Display/Overlay
72. • Display Command
• Relative Pick
• Momentary Contact
• Ramp
• Connect Variable
• Move Horizontal or Vertical
• Numeric/Text Entry
5.5.3 Faceplates
A faceplate is a dynamic representation of control block
parameters. Draw provides a complete library of faceplates, ready to be
connected to any control block in the control database. In addition, you
can build your own faceplates using the standard Draw drawing tools.
To configure a faceplate, you need only define the Compound:block to
which the faceplate is connected. Draw automatically determines the
proper configuration attributes for the associated Compound:block.
5.5.4 Trends
Trend areas represent changing data values from the real-time
database and historian database. A data is displayed as a series of plotted
points connected by straight lines and scaled according to the high and
low limits configured for each trend line.
5.5.5 Group Displays
Group displays allow you to group faceplates and trends into
unique layouts to meet changing operational needs.
73. 5.6 View
Figure 5.3 View
View is a window into the system software, providing a user-
friendly interface to the total process. You can interact with any or all of
the real-time plant, field, and process data available in the system.
View provides:
• Direct access to dynamic process displays.
• Entry into user-configurable operating environments specific to
each user - the process engineer, process operator, and software
engineer.
• Execution of embedded real-time and historical trending.
• Service and display of process alarms via the Alarm Manager.
• An overview of the compounds and blocks in the control database
and access to block default detail displays via Select.
• Access to other applications, such as:
o Draw software for building and configuring dynamic user
graphics.
o System Management Displays for monitoring system
equipment health.
o Integrated Control Configurator for configuring the control
database.
o Historian for configuring the historization of data and system
messages.
74. o Access to the four most recently used displays.
Additionally, with View you have:
• Flexibility in customizing environments to conform to your site
requirements.
• Rapid access to View while in other applications.
• Screen print utility.
• Window sizing options.
The multi-window capability of Solaris and Windows NT operating
systems allows you to monitor the information on a process control
display as well as access other applications without closing any window.
5.6.1 View Window
View Window contains the following features:
• A top menu bar for accessing displays, configurators, and other
applications as specified by the environment.
• A display bar of named display buttons or eight "thumbnail" mini-
display buttons for directly accessing process displays.
• A system bar with System and Process alarm buttons indicating
system and process health; a message bar with a dropdown list of
the latest messages; display of the current date and time.
• A status bar indicating the current display name, current operating
environment, Operator Action Journal logging name, printer
logging name, Historian name.
Using the control window menu, you can:
• Resize the View window automatically or manually.
• Move the window.
75. 5.6.2 Operating Environments
A collection of programs, utilities, and displays related to user
tasks is provided for each of the following: process operator, process
engineer, and software engineer. These environments, including menu
bars, menu content, and Display Bar content, can be modified to conform
to your site requirements. You can easily switch from one configured
environment to another. To secure environments against unauthorized
use, environment passwords can be configured and menu entries disabled
based on the environment.
5.7 Operator Action Journal
The Operator Action Journal is a record of specific operator actions
taken during process control operations. These actions generally consist
of manipulating certain Control Processor, and gateway parameters as
well as Application Processor, Application Workstation, and Workstation
Processor shared variables. Actions of this type are the ramping or direct
data entry of point values, toggling points, changing block statuses,
acknowledging block alarms, and horn muting. Operator action reporting
is limited to operator actions from the Display Manager, View, and
Alarm Manager. Also logged are environment change actions, scripts,
applics, and invoking other applications such as configuration.
When the Operator Action Journal feature is enabled, all operator
actions within the Display Manager, View, and the Alarm Manager that
change parameters in the process database are logged to a printer and/or
to the specified Historian database. These operator actions include
toggling points, ramping or direct data entry of new point values,
76. changing block statuses, acknowledging block alarms, and other actions
such as horn muting.
Information logged as a result of each database change includes:
• Name of the Display Manager, FoxView, or Alarm Manager that
requested the database change.
• Compound:Block.Point for which the change was made.
• The "old value" TO "new value" text for non-packed Boolean.
• Current mask and data value for packed Boolean/long.
Following is an example of an Operator Action Journal Report.
Operator Action Journal Report
Tue Aug 1 1997 17:04:05 Page 1
08-02-97 07:57:08 GC3E31 SCRIPT /usr/fox/hi/init.cmds
08-02-97 07:57:15 GC3E31 ChgEnv Init_Env ->Init_env
08-02-97 07:58:19 GC3E31 ChgEnv Init+Env ->Proc_Eng_Env
08-02-97 08:00:34 CG3E31 UC01_LEAD :SINE .OUT 16.18 to 46.18
08-02-97 08:00:54 GC3E31 UC01_LEAD :SINE .MA Manual to Auto
08-02-97 08:00:57 GC3E31 UC01_LEAD :SINE .LR Remote to Local
08-02-97 08:01:01 GC3E31 UC01_LEAD :SINE .MA Auto to Manual
5.8 Control Configuration
Process control for DCS is based on the concepts of compounds
and blocks. A compound is a logical collection of blocks that performs a
control strategy. A block is a member of a set of algorithms that performs
a certain control task within the compound structure. Figure 7.4 shows
the compound/block relationship.
The compound provides the basis for the integration of:
• Continuous control
• Ladder logic
• Sequential control.
77. Within this structure, any block in any compound can be connected to
any other block in any other compound in the system. The entire
compound structure can be viewed through the workstation display.
The block contains parameters that have values of the types: Real,
Boolean, Packed Boolean, Boolean Long, Integer, or String.
Figure 5.4 Compound/Blocks relationship
5.8.1 Compound Functions
The compound supports the following functions for the related blocks:
• Process alarm priority, alarm inhibiting, and alarm grouping
• Sequence status notification (see Sequential Control section)
• Phasing for execution load leveling at execution time.
5.8.2 Compound/Block Process Alarming
Alarms and status messages are generated by specific alarm blocks
and by alarm options in selected blocks. Alarms have five levels of
priority, 1-5, (where 1 = highest priority) that enable you to quickly focus
on the most important plant alarm conditions. An alarm priority of 0
indicates the absence of any alarm. These are summarized in a single
alarm summary parameter for each compound. This parameter contains
the priority of the highest current alarm in that compound. To reduce
78. nuisance alarms, alarms can be inhibited at the compound level on a
priority level basis. Alarms can also be inhibited at the block level, on
either an alarm type basis, or an overall basis.
Alarms are initiated by the blocks within the compound. Alarm
messages are then sent to groups of stations or applications (for example,
Workstations, Historians, Printers) according to configured alarm groups.
The UNACK alarm acknowledge output parameter allows the user to
propagate alarm acknowledge actions to all blocks in a compound.
Stations, applications, and devices corresponding to various alarm
destination groups are configured at the compound level or at the station
level in the case of station compounds.
Group numbers for individual block alarm types are configured at the
block level.
5.8.3 Compound/Block Phasing
A user-defined phase number can be assigned to each compound
using a range of integer values that varies with assigned period. Phasing
allows the starting time of one compound/block to lead or lag the starting
time of another compound/block, thereby leveling the block processor
load.
5.8.4 Compound Attributes
The compound has the following attributes:
• Name: User-defined name that must be system-unique and no more
than 12 characters in length. The name can be any mix of numeric
(0 to 9), upper case alphabetic (A to Z), and the underscore (_).
• Descriptor: 32-character field for user-defined identification.
• On/Off: Parameter that enables or disables the execution of all
blocks within the compound, where: 1 = on; 0 = off.
79. 5.8.5 Compound/Block Parameters
Compound and block parameters contain values that are of one of
the types Real, String, Integer, Short Integer, Long Integer, Boolean,
Packed Boolean, Packed Long, or Character. Additionally, parameters are
defined as being configurable, and either connectable/settable, not
connectable/not settable, or a combination that is dependent upon the
compound, block, and state.
5.8.5.1 Configurable Parameters
Configurable parameters are those parameters that can be defined
through the Integrated Control Configurator. They can be displayable
only, or displayable and editable.
5.8.5.2 Connectable Parameters
Connectable parameters are those parameters of the user interface
in which secured, change-driven connections may be made between
network stations, or as local direct connections within the same station.
Each connection consists of a connectable source and a connectable sink.
Output parameters (all outputs are connectable) are sources, while a
connectable input may be a sink or a source, or both.
Certain parameters that may be considered functional inputs (such as SPT
in the PID blocks, and RATIO in the RATIO block) are settable but not
connectable. A connectable parameter has a value record that contains the
parameter's value, its status, and its designated value type (Real, Boolean,
or Integer).
80. 5.8.5.3 Input Parameters
Input parameters are connectable types that are the receivers of
data from other connectable parameters via a path connection.
If no source path is specified during configuration, then the resident data
of the value record is the actual "source" of data. It can be either the
initial default or configured value, or a new value through a SET call to
the input parameter.
If a source path is specified, then the data value is an output parameter of
the same or another block, or a shared variable, thereby securing the
input. By linking a shared variable to a block input during configuration,
the user can establish a long-term secured connection between a remote
application program and the block input.
5.8.5.4 Output Parameters
All output parameters are connectable data sources that have value
records. There are two types: settable and nonsettable. The settability of a
settable output is controlled by the secured status of the value record. The
secured status is dependent on whether the block's operational mode is in
Auto or in Manual. In either Auto or Manual, nonsettable output
parameters cannot be written by any other source under any conditions.
Settable outputs may be conditionally released by the block
algorithm in the Manual mode. In Manual, the block unsecures settable
output parameters. They can then be written by other tasks via SET calls.
When the block switches to Auto, the block secures and updates its
output parameter(s).
81. 5.8.5.5 Nonconnectable Parameters
Nonconnectable parameters have no value records and are not
linkable. They mainly consist of string-type variables like NAME, or
nonsettable parameters that are used in the configurator only, for
example, block options. Local algorithm variables are also
nonconnectable. Nonconnectable parameters are generally accessible
through GET calls.
There is also a class of nonconnectable input parameters that comprise the
block user interface which can be manipulated through SET calls. An
example is an alarm deadband.
5.9 Role Play
Each trainee should introduce one of the main applications:
8. System Management.
9. Historian
10.Graphics Applications.
11.Control Configurator.
12.Operator Journal
13.Alarm System.