Control Systems
A clear control system scope of work helps you compare integrator bids on the same basis and reduce surprises during startup. Here is what to document before requesting quotes.
By Pro-Tech Systems Group, Akron, Ohio
Key takeaways
A control system scope of work defines project boundaries, existing equipment, required behavior, deliverables, and acceptance criteria. It gives integrators a common basis for quotes and helps reduce change orders.
A request to upgrade a programmable logic controller (PLC) or replace a human-machine interface (HMI) leaves too much open. One bidder may include code conversion only, while another includes wiring changes, drawing updates, and training. Those proposals describe different jobs.
Price depends on the existing system, sites, input/output (I/O) points and tags, communication methods, and panel additions or updates. Identify unknowns instead of leaving bidders to make different assumptions.
Pro-Tech Systems Group is based in Akron, Ohio, and provides PLC programming, control panel design and fabrication, and supervisory control and data acquisition (SCADA) integration. Review control system integrator questions alongside your control system scope of work so you evaluate engineering, testing, and support as well as price.
Use these categories as the backbone of your bid package. Mark missing information clearly and assign responsibility for confirming it.
State the operational goal and identify equipment included or excluded. Define interfaces with upstream equipment, downstream equipment, existing controls, and plant systems.
List PLC and HMI platforms, software versions, networks, installed I/O, and available spares. Identify current drawings, code backups, access credentials, and any documentation gaps.
Describe automatic sequences, manual operation, permissives, interlocks, and responses to faults or lost communications. State restart behavior and identify safety functions requiring separate review.
Separate hardwired signals, networked device data, and calculated tags. Include instrument ranges, engineering units, signal types, device locations, and required data collection.
Specify approved equipment, enclosure ratings, environmental conditions, wiring conventions, and spare capacity. If the plant requires an Underwriters Laboratories (UL) 508A listing, state that explicitly.
Identify required platforms, versions, runtime licenses, and development tools. Define ownership and transfer terms, source-file access, and secure delivery of credentials needed for maintenance.
List required displays, trends, recipes, operator controls, and access roles. Define alarm priorities, response expectations, acknowledgment behavior, and applicable plant alarm-management requirements.
Describe communication paths, segmentation, remote access, and firewall responsibilities. Identify who approves network changes and how backups and support access will be managed.
Require electrical drawings, panel layouts, network diagrams, commented source code, manuals, and as-built records. Specify editable file formats and when each deliverable must be submitted.
Define commissioning responsibilities, permitted outages, operator training, and maintenance training. Include warranty terms, support arrangements, schedule milestones, and the process for pricing changes.
Start with field information, then define operation and acceptance in your control system scope of work. Record unresolved items so bidders can identify allowances and exclusions rather than hide assumptions.
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Have qualified personnel inspect affected equipment under plant electrical safety procedures. Compare drawings with installed hardware and record discrepancies. Use this inventory when planning PLC upgrades and migration strategies.
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List local and remote I/O, instruments, drives, and communication protocols. Check device compatibility and required gateways rather than assuming existing connections will work with replacement hardware.
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Capture confusing screens, recurring faults, and manual workarounds. Separate requested improvements from existing behavior that must remain unchanged. Use those decisions to guide control system programming and test cases.
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Assign hardware purchasing, panel fabrication, installation, field wiring, instrument calibration, and network configuration. Name the party responsible for verifying each interface between contractors.
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Coordinate outages with operations and maintenance. If shutdown options are limited, request an engineered migration plan with temporary operating arrangements, rollback conditions, and safety review.
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Define required tests, records, training, and closeout documents. Require written approval for scope changes, including their price and schedule effects, before additional work begins.
A request for quote (RFQ) and its control system scope of work should describe requirements that bidders can verify. Attach equipment schedules and narratives rather than inserting arbitrary quantities or unsupported performance targets.
| Scope Area | Vague Wording | Clear Wording |
|---|---|---|
| PLC Migration | Upgrade the obsolete PLC. | Replace equipment identified in the inventory, preserve approved sequences, and document hardware compatibility and spare capacity. |
| HMI and SCADA | Provide new operator screens. | Develop displays from the approved screen list, including controls, trends, alarms, diagnostics, and access permissions. |
| Alarm Management | Alarm all critical points. | Configure alarms from the approved alarm list and plant philosophy, using ANSI/ISA-18.2 alarm management practices where specified. |
| Control Panels | Supply a new control panel. | Meet the specified enclosure, environmental, wiring, and listing requirements. Provide drawings for approval before fabrication. |
| Field Instruments | Connect existing transmitters. | Use the instrument schedule to verify signal compatibility, power requirements, scaling, and end-to-end readings. |
| Testing and Commissioning | Test thoroughly and help with startup. | Execute approved factory and site test procedures, record results, resolve deficiencies, and obtain owner sign-off. |
| Documentation | Provide software backups. | Deliver editable drawings, commented source files, license records, authorized access credentials, and final as-built documentation. |
A responsibility matrix in your control system scope of work assigns each task to the owner, integrator, or electrical contractor. Include both who performs the work and who accepts it.
Do not stop at broad headings such as installation or commissioning. Split tasks at the handoff points where missing materials, wiring, or approvals could delay startup.
Use separate entries for the following responsibilities.
This division also helps when reviewing SCADA system cost. A proposal should identify what is included, what the owner supplies, and what depends on field verification. Require bidders to flag deviations from the responsibility matrix.
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Assign purchasing, installation, programming, and testing responsibilities.
Include a factory acceptance test (FAT) and site acceptance test (SAT) in your control system scope of work. Define test coverage, witness responsibilities, acceptance criteria, and how unresolved items will be handled.
The FAT checks the system before shipment using simulated I/O signals. Verify logic, screens, alarms, and relevant panel wiring against the approved narrative. Record results for signature by the integrator and owner’s representative.
The ISA article on bypassing the factory acceptance test provides useful background for planning this work. Factory simulation cannot prove actual transmitter calibration, field wiring, motor rotation, or loaded process performance.
The International Society of Automation (ISA) publishes ANSI/ISA-62381, also designated International Electrotechnical Commission (IEC) 62381. It defines requirements and checklists for factory acceptance, factory integration, site acceptance, and site integration testing. The ISA-105 standards committee covers commissioning, loop checks, and factory tests.
After installation, use SAT procedures to verify field connections, instruments, equipment interfaces, and required operating sequences. Distinguish dry checks from process testing and obtain operating authorization before moving equipment. State whether acceptance and warranty commencement occur at the same milestone.
Check the control system scope of work package before issuing it. Give every bidder the same drawings, revisions, and written answers to clarification questions.
The document structure stays similar across industries, but a control system scope of work must include a control narrative that matches the process. Describe operating constraints rather than relying on a generic equipment specification.
For automated wastewater treatment systems, identify how treatment and collection operations will continue during cutover. Define approved temporary controls, reporting requirements, and remote lift station communication behavior.
Aeration uses a large share of wastewater plant energy. A dissolved oxygen control scope should address sensor placement, blower operating limits, air-header pressure constraints, and response to sensor failure. Instrument selection must match the measurement and installation conditions.
In metals production, describe feed accuracy, strip variation, tool protection, and recipe handling. That example does not define the requirements for another line.
Keep machine control, production data collection, and business-system interfaces distinct in the specification. Readers can call 330-773-9828 to discuss control system requirements with Pro-Tech Systems Group.
Pro-Tech Systems Group designs, programs and supports control systems from Akron, Ohio. Call 330-773-9828 or send us your scope.
A control system scope of work defines an automation project’s boundaries, equipment, required operation, responsibilities, deliverables, and acceptance criteria. Plant owners use it to give integrators a common basis for quotes.
A control narrative is useful even when converting existing programmable logic controller code. It identifies intended operation, separates approved behavior from legacy workarounds, and provides a basis for testing. Do not remove existing logic without reviewing its purpose.
A factory acceptance test checks the system before shipment using simulated signals. A site acceptance test checks the installed system, including field connections and required operating behavior. Define which tests need actual process operation and which can be completed without it.
Identify missing drawings, inaccessible code, and uncertain wiring in the control system scope of work. Assign field verification before final design, or request a separate discovery task. Require bidders to explain assumptions and how newly discovered work will be approved.
Specify plant ownership where available and appropriate under the software vendor’s terms. Require editable source files, backups, license records, and authorized maintenance access. Security credentials should be transferred securely, not removed simply to make the system easier to access.
Control system pricing depends on the existing system, sites, points and tags, communication methods, and panel additions or updates. Document those conditions and request clear assumptions and exclusions. A clear control system scope of work improves comparison but does not guarantee a particular price.