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Associated Engineering believes that no one solution or vendor
can best meet the varied requirements of a control system. Therefore, to develop
a new control system that is both cost effective and will meet client needs, the
scope of the project must first be defined. This is accomplished by review of
the available background data and through discussions with client management and
operating staff and between process and instrumentation system designers. While
client involvement is encouraged throughout the project, it is at this stage that
a thorough and open dialogue is undertaken to establish the project requirements.
Communication is desirable with all staff whom the system will affect.
Available methods for communication include staff questionnaires, personal interviews,
group sessions and workshops.
After this stage a preliminary assessment of
the control system needs is made by defining:
- the
process control requirements.
- operational philosophy.
- type of instrumentation and signal count.
-
operator interface needs.
- anticipated analog signal manipulation.
- the required data base and;
- the
relative physical location of the control system components.
Once a process flow diagram has been established, the control
system functional description proceeds with the development of the process and
instrument diagram (P&ID). The development of the P&ID also allows the
instrument tagging system to be put in place and an input/output signal listing
defined for the whole plant or system.
The functional description (control
philosophy) is an important step in the design process as it explains how the
designers will fulfil the project control requirements. The functional description
is a detailed description, at the equipment level, of the plant control operation
to be used for the project. In turn, it is used to define the tasks to be performed
by programmable devices. This functional description will be checked and reviewed
many times before becoming final. The functional description reviews include those
needed for internal design and client reviews to establish operational procedures.
At this
stage the control system that is best suited to the particular plant or system
is defined. The criteria include the degree of automation required, client management
and operator needs, the size of the process being controlled, the reporting methods
to be adopted, the response time required of the control system, etc.
If a programmable control system is indicated then consideration has to be given
to establishing the most appropriate system architecture. These considerations
include:
- the type of operating system.
-
local area network, wide area network or other communication data transfer needs.
- connectivity needs of the system for various manufacturers
equipment.
- the control system hierarchy that may integrate
several levels such as a field bus network, an operating system network and a
management information system network.
- the need to remotely
transmit process signals or data.
- system reliability and
redundancy.
- diagnostics and maintenance.
-
future expansion.
Associated Engineering has developed methods to evaluate
the multitude of choices available. The result is a system that is customized
to suit the project's needs.
Process design parameters, and thus the process variable range of measurement,
are established with the process designer. The field instruments may then be specified.
Service conditions such as the process gasses, fluids or solids and required material
compatibility are considered.
The control equipment is specified to
meet the requirements of the firm functional description and agreed control methods.
Final specifications include detailed equipment specifications, instrument
specification sheets, system input/output lists, cable schedules, equipment mounting
and termination panels, control console specifications and other required technical
data required to fully define the supply of materials. Associated Engineering
has tools to help automate production of these specifications in conjunction with
the drawings to produce an accurate design at a lower cost.
Construction drawings include floor plans, instrument block
diagrams, control schematics, P&ID's, system integration, control panel layouts,
wiring drawings and loop diagrams etc. These drawings provide information on instrument
locations, cable routing, control and readout panels and other instrument details.
Computer aided drafting (CAD) and integrated design is used extensively in order
to produce accurate and clear drawings cost effectively.
A consistent
tagging system is used on the drawings that is cross-referenced with the control
equipment and field instrument database. Accurate cross-referencing helps to ensure
that the control system design is complete. The tagging system also helps the
installing contractor to fully define the scope of the construction work. This
reduces the potential for claims during construction.
For many projects, the cost of the control
equipment and the programming exceeds the cost of the instruments, cables, panels
and installation. For these projects substantial cost savings can be realized
by directly purchasing the major equipment. Associated Engineering can specify,
evaluate and procure this equipment. Receipt of this equipment also enables the
programming work to begin earlier in the project, resulting in a shorter construction
period. Full tendering services are available for that work to be let to a Contractor.
With client consultation, various tendering approaches are considered.
The traditional open bid system is not always the most suitable for some situations.
A lower cost, lower risk approach may be more suitable depending on each case.
A competitive specification and tender for a control system can lead
to the submission of equipment from different manufacturers that will vary in
ability to achieve the defined requirements. The many intricacies of different
offerings are evaluated by Associated Engineering to ensure that the most appropriate
system is recommended.
Control system equipment configuration usually involves programming control devices
with logical sequences, plant data and operating parameters to implement the control
philosophy. The setup of smart transmitters, digital loop controllers, PLC, DCS
and computer software programming, operator interface configuration, and communication
equipment are included in the overall configuration procedure. To test particular
control strategies, mathematical system, or subsystem, models may be required.
Statistical process control methods may be used in conjunction with the installed
data base.
Associated Engineering undertakes system configuration based on
learned efficient programming experience to achieve the functional description
requirements of the control system.
To address each requirement of the
control philosophy, detailed control algorithms are developed before the start
of coding. On more complex projects, the programmer(s) may elect to perform a
pseudo code stage in the program development where each logical step for each
algorithm is written out in English or a symbolic language. Once satisfied that
the programming requirements have been well defined, the actual code is written.
The program is documented as it is developed to simplify de-bugging and ensure
that relevant details are recorded.
Performance of the ladder logic
and other programming is checked by pre-assembling the system at one of Associated
Engineering's test facilities. Signal simulators, "soft" processors
and equipment manufacturers test equipment and methods are used to prove the system
configuration. Methods have been developed to efficiently test and criticize programs
and configurations to reduce on-site program changes and software trouble shooting.
The operator interface is developed with close client consultation so
that the interface presents plant and process data to the operator in ways that
are the most useful, understandable and fit the operating philosophy employed
at the plant. Mock-ups of the process screens are prepared and discussed with
the operations and management staff. Navigation methods, on-line help, security,
control and access to process setpoints are all defined. Groups of points for
trending and reports may be pre-configured for fast and convenient access and
wide area data transactions if appropriate.
Following system configuration,
documentation of the programs is completed to reflect the final code. This documentation
allows the configuration program(s) to be more easily understood by operations
staff or following designers.
Design records include record drawings, maintenance manuals, documented configuration
coding, design calculations, wiring diagrams, operation procedures etc. Such records
provide the documentation necessary for control system maintenance, troubleshooting,
and to extend or modify the control system in the future as need arises.
Associated Engineering gives careful attention to the assembly and binding
of design records. The importance of being able to readily recover design information
is recognized.
Fully documented source code is provided. Associated
Engineering's clients have complete access and freedom to modify the system as
desired in the future. The company has employed this policy for over ten years,
staking future involvement with the control system on the quality of the work
and the level of service provided.
Instrument calibration sheets give
the manufacturer's technical data for the model used and the measurement ranges
in engineering units.
Configuration for programmable devices is fully
documented in a consistent format from one project to the next allowing easy retrieval
of readable program details.
During programming and configuration, the
operator interface software is configured to provide an intuitive working environment
which provides the operator with on-line information. In addition, comprehensive
operation manuals are prepared. These operation manuals cover: -
a description of the control system.
- step-by-step instructions
for each control function or task.
- normal operating procedures.
- special operating procedures such as system start-up or
operation with partial failures.
- system diagnostic procedures.
- troubleshooting and sources for technical support.
After checking the programming,
the entire pre-assembled system is tested in-house to ensure that the components
are functional before disassembling the system and shipping the equipment to site
for installation, start-up and commissioning.
Start-up consists of putting
into action individual equipment or equipment groups, loop testing of wiring systems,
electrical testing, etc. Commissioning is the orderly starting of the total system,
including the analysis of the plant operation.
During start-up and commissioning,
final adjustments are made to instrument calibration, the system configuration,
the functional description, protection systems, etc.
The complete documentation
includes final "as started" instrument calibration sheets, continuity
test results, insulation and other electrical testing results. The manufacturer's
start-up record and performance record for each piece of equipment is included.
Such documents provide a base for the operator to work from, a place where he/she
can mark-up future changes and a reference to the equipment parameters; pressure,
flow rate, speed, current, etc. at the time of start-up for on-going use.
Equipment information is extremely important for the on-going operation and
maintenance of the plant. The current condition of a pump, motor, electrical cable,
ventilation unit, etc. can often be judged by comparison between present test
results and parameter measurements and those made at the time of start-up. These
recorded measurements are therefore an important part of the plant documentation.
Full training services for operations, maintenance and administration
staff are provided. As informal training, involvement of the staff during start-up
and commissioning is encouraged. Before system completion formal training sessions
are held for a variety of subjects such as: end-user operations staff, maintenance,
administration tasks, system operation, and programming.
Completion of commissioning does not end Associated Engineering's
involvement. Support is available either by telephone or site attendance. Where
appropriate, modems can be provided which, with client authorization, permits
remote connection to the PLC's or the operator interface to diagnose problems
and make adjustments.
Associated Engineering offers system maintenance
contract services to: - Debug and trouble-shoot the software.
- Install software upgrades.
- Periodically
back-up the database and graphics screens.
- Check and clean
the hardware.
- Make adjustments identified by the operations
staff to further optimize the system.
- Provide advice and
assistance.
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Instrumentation 
Custom
Control
