As a control systems engineer/PLC/HMI programmer, automation professionals are often required to develop a control system based off of a specification provided by a SME (Subject Matter Expert) on a piece of machinery or process. Control systems engineers rely on these SME’s to provide accurate and detailed information on the desired operation of a control system. The information provided to the engineer will prove to determine the overall development time and delivery of an accurate solution to the end user.
In systems integration, there is a typical list of information that an integrator will require to execute a project from start to finish. This information will vary, depending on the scope of the project, but the minimum required information will stay the same, regardless of scope.
- A sequence of operations will need to be provided in some form or fashion from the SME. The typical formatting for this sequence of operations could be built as a cause/effect table, flow chart, logic diagram, or even in a text format. This information will determine the high-level layout of the PLC/HMI program by calling out specific field devices and control operations that determine what logic needs to be executed within the control program. Depending on how detailed this document is, the integrator may also be able to determine I/O count and device configuration as well.
- Depending on the application, whether the project is being executed for a machine or process, some type of mechanical layout of the system should be provided to the control systems engineer in order to visualize the sequence of operations. This documentation can be provided as a P&ID (Piping & Instrumentation Diagram) for process control applications, and as a mechanical equipment layout in machinery and manufacturing equipment applications. Having a visual representation of the system will assist in the overall development of the project by providing an overall flow of what is portrayed in the sequence of operations.
- If not specified in either the mechanical layout or the sequence of operations, field device level specifications will be required to define what input/output modules will be needed to connect to each device. This step can be overlooked, but is a crucial part of building an accurate materials list for the control system hardware design. The need for this information will be determined by the scope of the project. In some cases, field devices are a specification requirement provided by the control systems engineer. Things to consider for I/O configuration include (but are not limited to):
- Voltage requirements for discrete inputs/outputs
- Input and output signal specifications for analog devices
- Supported communication protocols for smart transmitters and sensors
- Recommended circuit protection for I/O devices
- Once all required information has been collected, the control systems engineer has the responsibility of building a template for the hardware/software design of the control system. This includes selecting properly sized and rated materials, and CAD drawings to fit the needs of the project. By utilizing the information provided by an SME, the control systems engineer has the ability to implement a design strategy for the control panel(s) with associated hardware, panel(s) design, and pseudo code implementation within the PLC/HMI.
- Other considerations in an automation project are completely dependent upon the overall scope of the project. Information that might need to be included would be specific industry standards that need to be followed and considered during hardware or software design. An example of this would be the IEC 61131 standard that calls out specific architecture and programming standards with a PLC control program. Some end users require control logic designed and implemented in a specific way to standardize assets across the board. From a hardware standpoint, the project could require devices that have to be mounted in classified areas designated by OSHA (Occupational Safety and Health Administration) as a hazardous location. Depending on the area’s classification, there may be a need for specially rated hardware in certain locations.
Automation project specifications can include a broad variety of information that is relevant to the successful completion of a project. But with that being said, the considerations called out in this blog are defined as an overview of the bare minimum requirements in the development of a controls project, and should not be overlooked. Collecting this information prior to engaging in a project will definitely save a controls engineer considerable time in development, and a ton of heartache.