New to Controls? We can help!
If you’re new to the automation world, we can help you get going! There are some basic steps and documents which will help you through the process, from concept to installation. These documents build on one another and are used to inform everyone how the system works; from management, to the installation group, to the programmer developing the code, these documents are what tell an individual what he or she needs to know. This documentation is part of an essential step-by-step process needed to create not just an automated system, but one that functions properly and exactly as intended. The sample documents attached below (click on the blue links to view) were used to program a very real system for a client on a very tight budget.
Control Narrative: The control narrative describes the functionality of your system. It contains a high-level description of how the different equipment being automated will function and a mid-level description of how each device is controlled (including the function of its sub-components). For example, you may have a simple pump you want automated. The control narrative would state what turns this pump on or off, perhaps a tank level. It would also include things like safety devices that shut the pump down (high vibration or low oil level switches, for example). If this pump was connected to a variable frequency drive (VFD), the control narrative would indicate any control conditions for that as well, perhaps stating that the pump speed is to be proportional integral derivative (PID) controlled based on tank level, maintaining a consistent level based on an operator set-point.
Instrument List: The instrument list is a spreadsheet detailing the devices connected to the control system. Every switch, transmitter, temperature device, motor contactor, VFD, and any device connected and controlled by the programmable logic controller (PLC) is included in this list. The spreadsheet shows where each device connects to the system, the type of interface it uses (digital or analog), and any scaling ranges or limits associated with an end device. Many devices will have more than one connection to the control system. For example, a motor contactor, which is used to turn a pump on and off, usually has both a run command from the PLC as well as a run status feedback to the PLC. The run command would be a digital output from the PLC to close the contactor and the run status would be a digital input to the PLC from a dry-contact or switch on the contactor that closes when the motor is running.
Shutdown Key / Cause and Effect: A shutdown key is a spreadsheet that contains an Input Verses Output list describing what action the control system takes when its input data changes. For example, most sites have Emergency Shutdown buttons connected to the control system. The shutdown key will tell you what happens when you press the big red button; what equipment is shutdown or what valves open/close.
Control System Drawings: Control system drawings are electrical schematics which show how the control system is wired and connected to its end devices (usually in a rack, card layout). Electrical drawings are also essential to the process and show wiring that is not directly involved with the control system. For example, a pump or motor 3-phase wiring, high voltage, or single-line diagrams. Drawings may also include a cable schedule showing where electrical cables go, for example.
P&ID Drawings: The Piping and Instrumentation Diagram is essential in developing the control system layout.
PID: A Proportional Integral Derivative controller (generally referred to as a control loop) is used in system control.
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