Modern plant control centers and operator control concepts

Modern_plant_control_centers_and_operator_control_concepts
 

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A white paper issued by: Siemens. © Siemens AG 2012. All rights reserved.

February 10, 2012

Summary

This article presents a user-centric concept for structuring indus-
trial process control. The background to this concept is the con-
stantly increasingly complexity of the processes to be monitored
and the working environment in control rooms from the perspec-
tive of the operators. The use of modern plant control centers
and operator control concepts can support and offload operators
in the execution of their tasks by means of a powerful human
machine interface. Modern plant control centers
and operator control concepts
HMI+ supports operative process
control of industrial production
processes by means of user-centric
process visualization
Dipl.-Ing. S. Kempf, Siemens AG, Karlsruhe
Dipl.-Ing. L. Glathe, Siemens AG, Frankfurt

A white paper issued by: Siemens. © Siemens AG 2012. All rights reserved. White Paper | Modern plant control centers and operator control concepts | February 10, 2012 2
Content
HMI+ supports operative process control of industrial
production processes by means of user-centric process
visualization…………………………………………………………………… 3
1. Introduction ……………………………………………………………… 3
2. Concept of user-centric process visualization ……………………… 3
3. Display and operator control concept using the example of
a batch column…………………………………………………………… 6
4. Conclusion ……………………………………………………………….. 8
Bibliography…………………………………………………………………………….9

A white paper issued by: Siemens. © Siemens AG 2012. All rights reserved. White Paper | Modern plant control centers and operator control concepts | February 10, 2012 3
1. Introduction
The primary task of the operator is to carry out
operative process control on the basis of process
and plant information from the production process
and its logistics and auxiliary processes [1].
Operative process control aims to maintain the safe
operation of the production plant in accordance
with requirements, to maximize the availability of
the production system despite isolated faults, and
to guarantee product quality despite fluctuations in
raw material quality, faults in the plant, and varia-
tions in throughput [5].
Finally, the process sequence must be optimized
with regard to costs, quality and safety.
The operator’s primary tasks are extended in par-
ticular by high cost pressure, for example through
material planning tasks, broader quality assurance
and efficient operation of the plant.
These extended tasks are traditionally contained in
the area of the plant control level.
The required information is presented to the opera-
tor in centralized control structures, mainly via the
display and operator control components of the
process control system in the control room. Fur-
thermore, additional information from a heteroge-
neous system world, e.g. PIMS, ERP, LIMS etc., must
be supplied to the operator and presented in rela-
tion to the task. This heterogeneous automation
landscape increases the complexity of the working
environment of control room operators.
In addition, the rising level of automation of today’s
industrial production processes results in a reduc-
tion in the number of control room personnel and,
in parallel, in a sharp increase in the volume of
process information to be monitored by each opera-
tor, caused, for example, by combining control
rooms.
This increasing complexity in production processes,
as well as the working environment in control
rooms, makes it difficult for operators to form a holistic mental picture of the plant and
processes to be monitored. But precisely this men-
tal picture is hugely important for monitoring the
status of the plant/process.
The use of user-oriented and task-oriented concepts
offers a solution to this problem. These are aimed
at creating integrated work systems, i.e. combined
optimization of the application of technology, or-
ganization, and qualification of the user. Instead of
adapting people to technology, technology must be
adapted to people [2].
Starting from the planning phase of process plants,
these aspects of user-centric process visualization
must be sufficiently taken into account in the de-
sign and conceptual definition of plant control
centers and operator control concepts.
This user-centric human machine interface (HMI),
referred to below as HMI+, has a crucial share in
this. In the remainder of this article, special atten-
tion is given to the design of operator consoles and
their elements and structures.
2. Concept of user-centric
process visualization
The display and operator control concept for plant
operators has changed significantly in recent years.
Where previously mosaic panels were used for op-
erator control, today the operator sits at a PC work-
station with, for example, 4 screens. Until now, the
benefits of the mosaic panel and recorder, such as
clear representation of process states, were rarely
adopted for PC workstations. Rather, the focus was
on eye-catching graphics which were, however, of
no great benefit in performing the actual operator
task.
Visualization systems and processes used today
achieve positive results only in some areas; for
example, individual plant sections or sub-processes
can be clearly represented using graphics displays.HMI+ supports operative process control of industrial
production processes by means of user-centric process
visualization

A white paper issued by: Siemens. © Siemens AG 2012. All rights reserved. White Paper | Modern plant control centers and operator control concepts | February 10, 2012 4
The systems are characterized by:
x A mishmash of different devices and software
products with non-homogenous operator inter-
faces
x Multiple input and output devices per PC at the
operator workstation
x Standard configuration of operator workstations
(e.g. always 4 screens per client)
x Cost-driven workstation design
However, the processes used to represent process
values display weak points with regard to the fol-
lowing
x Display of the overall status of the process – the
big picture
x Operators receive information predominantly
through the use of alphanumeric displays instead
of analog representations with pattern recogni-
tion
x Attraction of the operator’s attention by means
of shape-coding and color-coding
x Task-related and activity-related visualization
x Display of information

Fig. 1: HMI+, user-centric concept for designing industrial
process control in accordance with [3]
The concept and design phases are also accompa-
nied by conceptual weaknesses:
x Process pictures are created on the basis of iso-
lated piping and instrumentation diagrams with
a different display purpose
x Particularly in new plants, it is not possible to
involve the operating personnel in the design
process at an early stage
x Lack of a process visualization standard encom-
passing all devices
x Lack of process know-how in the design process
HMI+, a user-centric concept for designing indus-
trial process control, is described below (see Fig 1).

A white paper issued by: Siemens. © Siemens AG 2012. All rights reserved. White Paper | Modern plant control centers and operator control concepts | February 10, 2012 5
This concept combines thoroughly familiar ele-
ments and structures of operator control units, such
as operator interfaces and their procedures, with
the design of operator consoles and control rooms,
and organizational measures to form a holistic solu-
tion approach.

The starting point for all considerations is the de-
tailed analysis of operator tasks with regard to
process control and additional tasks in the control
room area (see the examples in Table 1). This analy-
sis must be carried out specifically for each plant on
a project-related basis and with the involvement of
the team of operators.

No. Task Job function Activity Requirements for process visu-
alization 1 Process control Monitoring an automated
plant Monitoring essential
operating parameters
(process-related KPIs) Overview displays with essential
operating parameters of the
plant to be monitored
Display of the permissible toler-
ances
Display of limit violations
Display of alarms and their
priorities
Analog displays for “pattern
support”
Trend displays for assessing
situations and deciding on
operating strategy 2 Process control Monitoring an automated
plant Detecting/perceiving
faults Attracting attention by means of
color scheme with distinct alarm
colors
Avoidance of cognitive
overload 3 Process control Monitoring an automated
plant Finding/identifying the
cause of the fault Jump function from alarm page
to the measuring point in the
process picture 4 Materials plan-
ning Planning materials Entering recipe parame-
ters Uniform and device-neutral
presentation of the operator
screen forms
Use of the same input and out-
put devices as for process con-
trol 5 Documentation
for process
control Keeping a shift logbook Entering the relevant
process value in the shift
logbook Presentation of all relevant
process values (in a log) 6 Extended quality
assurance Monitoring of quality-
related process parameters Monitoring of quality
KPIs Visualization of quality KPIs in
overview displays of the process
control system
Device-independent, homoge-
nous presentation of the quality
KPIs Table 1: Requirements for process visualization resulting from operator tasks

A white paper issued by: Siemens. © Siemens AG 2012. All rights reserved. White Paper | Modern plant control centers and operator control concepts | February 10, 2012 6
In addition to project-specific issues, the following
generally valid issues for improving process visuali-
zation have been derived from the prioritization of
the requirements for process visualization (cf. Table
1):
Procedure for representing process values:
x Additional use of abstract operator procedures in
which the process topology plays a subordinate
role. For example: process-related overviews
with essential operating parameters of the plant
to be monitored in an arrangement of hybrid
displays with tolerance and limit value visualiza-
tion that supports pattern recognition. The oper-
ating parameters to be displayed are selected in
interaction with the operating personnel accord-
ing to certain criteria. Around 80% of operator
input and monitoring during normal operation of
the plant takes place from these overviews.
x Partial replacement of alphanumeric displays
with analog displays, hybrid displays (analog and
status display), and trend representations.
x Reduction in the complexity of the process flow
diagrams thanks to task-oriented and process-
status-oriented selection of the process values to
be represented (dedicated representations for
start-up and shutdown, normal operation, load
change, and diagnostics)
x Use of a color scheme including alarm colors
x Process picture representations as a component
in organizing the operator console
x Representation of information instead of data,
e.g. innovative representational objects for tem-
perature distributions, or trend curves for assess-
ing situations and deciding on operating strate-
gies
System solutions:
x Multifunctional integrated operator workstation
with homogenous operator interface, operator
control with the same input/output devices
x Applications of all individual devices in accor-
dance with a device-wide style guide for process
visualization
x Configuration of the operator workstation as
part of the organization of the operator console
x Ergonomic design of the operator workstation
x Design of the control room as the living space for
the operators Measures in the concept and design phase:
x Specify the process visualization concept in the
style guide of the process visualization system
x Integrate the users (operating personnel) into
the design process at an early stage. If this is not
possible, the abstract representations must be
created later in the optimization phase
x Involve experts with process know-how
The concept is based on the rules and recommen-
dations fur the structure of displays where screen
systems are used for process control listed in
VDI/VDE 3699 “Process control using display
screens” [4].
The recommendations in that document are con-
tinued in this concept and placed in the context of
user-centric process visualization.
3. Display and operator con-
trol concept using the exam-
ple of a batch column
The concept described in the previous section is
explained below using the example of a distillation
column.
The tasks of the operator of a distillation column
are:
x Starting up and shutting down the distillation
column
x Monitoring the process-related characteristic
variables, e.g. differential pressure
x Responding to changes in pressure (fraction
change) at the head of the column
x Responding to alarms
These tasks are taken into account in the display
and operator control concept to guarantee an opti-
mal working environment for the operator.
An overview display is selected for monitoring the
process-related characteristic values. This contains
the important process values and closed-loop con-
trols of the column. This display has the advantage
that large volumes of data can be combined for the
condensed presentation of information.

A white paper issued by: Siemens. © Siemens AG 2012. All rights reserved. White Paper | Modern plant control centers and operator control concepts | February 10, 2012 7

Fig. 2: Overview diagram of the column

The task “monitoring the head pressure” is effec-
tively supported by a trend display on the operator
screen. At a constant head temperature (T1001),
the head pressure (P1002) drops significantly when
changing from one fraction to the next. The opera-
tor must respond to this by changing the draw-off
tank.
The task “monitoring the differential pressure”,
especially following a fraction change, is supported
by a trend display showing the permissible toler-
ance band. The differential pressure (P1003) is a
measure of the gas load in the column and must be
kept approximately constant. This is why the opti-
mal working range is represented in the trend dis-
play.
Other important characteristic variables repre-
sented include the energy consumption of the plant
and the reflux ratio.
New hybrid displays enable the evaluation of the
process values. These visualize the acceptable
range for the process value. Otherwise, evaluation
using an analog value would be possible only with
experience.

Fig. 3: New hybrid display
Another example of evaluating process variables is
the representation of the temperatures in the col-
umn.
Evaluating the process status using the tempera-
tures as analog values can only be done with expert
knowledge (cf. Fig. 4; are the temperatures within
the optimal working range?).

Optimal Operating Range
Prozess Value with Measure
(Visualization of an Alarm)
Alarm Indication Alarm (High Limit)

A white paper issued by: Siemens. © Siemens AG 2012. All rights reserved. White Paper | Modern plant control centers and operator control concepts | February 10, 2012 8
Fig. 4: Typical view of a distillation column
If the temperatures are instead visualized as a
temperature curve showing the optimal working
range, the evaluation can be done via the picture.
(cf. Fig. 5; one temperature is not in the optimal
working range).
Fig. 5: View of a distillation column with vertical temperature
curve

4. Conclusion
The suggested user-centric visualization concept is
intended as a holistic solution approach for effec-
tively coping with the increasing complexity of the
processes to be monitored and the working envi-
ronment in control rooms from the operator’s per-
spective.
Many aspects justify investment in modern human
machine interfaces or call for redesigning of tradi-
tional operator control concepts: safe operation of
production plants through avoidance of operator
errors, extension of operator tasks, loss of operat-
ing know-how through fluctuations in employee
numbers, and, not least, increased work load result-
ing from the merging of control rooms. Initial ex-
periences in application argue in favor of the use of
these concepts.

A white paper issued by: Siemens. © Siemens AG 2012. All rights reserved. White Paper | Modern plant control centers and operator control concepts | February 10, 2012 9
Bibliography

[1] NA 120 “Operator Workplace from the Human-Process Communication Point of
View”
[2] Wickens, C.D., Holland, J.G. (2000). Engineering psychology and human perform-
ance. New Jersey: Prentice Hall.
[3] EEMUA 201 „PROCESS PLANT CONTROL DESK UTILISING HUMAN-COMPUTER IN TER-
FACES – A Guide to Design, Operational and Human-Computer Interface
Issues“
[4] VDI/VDE 3699 “Process control using display screens”
[5] Charwat, H.J. Lexikon der Mensch-Maschine Kommunikation
(Lexicon of human machine communication)

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