Specification documents: Pay now or pay later

Back to Basics: Planning a control system can be implemented using specification documents that are formatted very simply and easily understood by the non-control system engineers.


Navigating the dark, rocky waters of control system development can be challenging for even the very experienced project managers. Control system activities, such as estimating, planning, and building, seem like some kind of black box magic. Many aspects of an automation project can easily be miscommunicated or not thoroughly understood, or just simply the wrong control strategy is applied to achieve the overall production requirements.

So many pitfalls can turn a basic control system project into a sinking ship. However, the risk can be removed by following the "Beacon Light of Specifications," which provides a proven, structured approach to developing an automation project and can keep a ship sailing to smooth waters. 

What are specification documents?

Specification documents provide a written description that uses basic terms to allow the end user to understand what is being defined without having to be proficient at distributed control system (DCS) or programmable logic controller (PLC) programming. Specification documents are comparable to a set of house plans. Would you write a check to your contractor and say, "Build me a house," without providing a floor plan? The answer is no.

The same is true for building an automation system. If you want a project to be successful and deliver what you expect, then a plan detailing what should be achieved is necessary. Planning a control system can be facilitated by using specification documents, formatted very simply and easily understood by the noncontrol system engineers. Using simplified language, these documents provide very specific target functions to allow all stakeholders involved to understand what otherwise may be a potentially intimidating process.

FS and DDS

Functional specifications (FS) and detail design specifications (DDS) are two flavors of the automation system specification documents.

Functional specifications generally define the big picture or overall functionality of systemwide functions. FS documents include software specifications or batch specifications. These typically define the common elements and/or tools used across multiple instances in the system.

DDS documents typically focus more on a specific application or on process-related functions, such as: equipment module sequences, interlock matrix functions, and automated logic conditions. A typical control system has FS and DDS documents to completely encompass all functions.

In addition, FS documents can be developed and used for bidding purposes for accurate quoting and bid comparison. Once the project is awarded, DDS documents can be developed to outline details of how to achieve FS functions identified. 

Specification benefits, best practices

Benefits of owning specification documents include the ability to:

  1. Provide means to generate an accurate quote.
  2. Define exactly what an end user will receive.
  3. Establish a scope boundary for the project.
  4. Enable generation of a preliminary schedule.
  5. Determine automation goals for the project to be successful.
  6. Generate reference documents for acceptance testing.

When developing specification documents, best practices include:

  1. Getting all parties involved early, including engineering, production, maintenance, quality, and other stakeholders
  2. Defining all terms so everyone is on the same page
  3. Organizing documents and providing a road map so everyone understands overall objectives
  4. Identifying how exception conditions are generally handled
  5. Using a class-based approach as much as possible to reduce design, implementation, and testing time
  6. Performing one example of each document type first and reviewing to ensure everyone's interests are represented.

Meet production requirements

Specification documents are a critical part of a successful automation project. The benefits of planning and documenting the software and hardware functions will ensure the end user will receive exactly what is needed to meet the production requirements.

Designing a system on paper allows for everyone to assimilate the available features and provide a mechanism to account for details to ensure nothing is overlooked or missed. Developing an overall FS document early on allows for accurate quoting and development of a general timeline of execution to ensure the project is delivered on budget and on time.

Robbie Peoples is a Project Manager & Lead Systems Engineer at Innovative Controls. Courtesy: Innovative ControlsDeveloping accurate specifications for an automation project can be an exhaustive effort, but with proper organization and support from all stakeholders, this task can be streamlined and made as efficient as possible. Specifications allow for the removal of the unknown and provide a navigational beacon to avoid the rocky waters of risk. Not all projects require the good automated manufacturing practice (GAMP) validation model level of documentation, but with a customer-focused approach, specification documents will set up a project for success.

- Robbie Peoples is a project manager and lead systems engineer at Cross Company Integrated Systems Group. Edited by Joy Chang, digital project manager, Control Engineering, jchang@cfemedia.com.

Key concepts

  • Specification documents are a critical part of a successful automation project.
  • Specification documents provide a written description that use basic terms to allow the end user to understand what is being defined without having to be proficient at controller programming.
  • Specifications allow for the removal of the unknown and provide a navigational beacon to avoid the rocky waters of risk.


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