Automation of Water Resource Recovery Facilities. Water Environment Federation

      When writing the PCN for system resets, the designer should describe when resets are necessary and how each one functions, especially for complicated systems with multiple subsystems. Typically, reset functions release all latched alarms and associated permissives so the automatic control system can function normally. Associated permissives refers to all conditions that must be satisfied before the equipment can be started; they are monitored by sensors, the signals of which are wired to the control system.

      Process control narratives should include a list of all remote indicators (e.g., alarms, monitored setpoints, status lights, etc.). A remote indicator is any indicator at a site other than the equipment’s local control panel or station.

      The PCN should include local pushbutton control stations for manual operations, maintenance, and testing. Designers should specify the type of controls and indicators needed such as start and stop, local or remote, speed control, and status lights (run, stop, fault, etc.).

      The PCN should specify which equipment must have UPS power in case the utility’s main power source fails. Designers should not only note this information, but also which equipment can withstand a short power interruption (minutes) until on-site generators are fully online; designers should also calculate the power load and duration (in minutes) required. This information should be shared with the project’s electrical engineer. Particular attention should be paid to associated network devices (switches, routers, and media converters) to prevent a situation in which equipment does not transition properly during outages because of lack of communication.

      The PCN should provide simple descriptions of vendor-supplied package controls, their functions, and which parameters must be monitored or controlled remotely. Designers also should provide all related vendor information (e.g., functional descriptions, control panel drawings, wiring schematics, and equipment catalog cuts) to I&C and electrical engineers as soon as possible. In addition, designers should let I&C engineers know what instruments the packaged equipment will need that are not provided by the vendor so that these instruments can be included in I&C specifications. Finally, to ensure that the design is well coordinated, I&C and electrical engineers should be asked to review packaged-equipment specifications. Every effort should be made to match existing packaged control system (PCS) hardware whenever possible to alleviate long-term O&M requirements for facilities. The specifications should require that all licenses and copies of programs for all PCSs be provided to owners for maintenance if the owner desires.

2.1.1.12 Programming Standards

      The following standards, in particular, should be considered when specifying programming standards (see Chapters 13 and 14 for more details):

      • Programmable logic controller programming standards,

      • Graphics standards, and

      • Alarming standards.

2.1.1.13 Field Instruments

      The following items should be considered when specifying field instruments (see Chapters 8 and 9 for more details):

      • Online analyzers and

      • Physical parameter instruments.

2.1.2 Drawings

      2.1.2.1 Process Flow Diagrams

      A PFD is a simplified facility process diagram that shows key process equipment, key process variable measurements, and other elements and their interconnections. Typically, PFDs are prepared by process engineers early in the project cycle and represent the precursor documents from which detailed P&IDs are developed. For additional information on PFDs, see Instrumentation and Control Systems Documentation (Meier and Meier, 2011).

2.1.2.2 Process and Instrument Diagrams

      Process and instrument diagrams typically are the most important design documents for a control system because they define the process, physical facilities, interconnections between units, measurement types and points, control elements, and control loops. These documents reflect the consensus of the designer and owner, and help design teams coordinate their efforts.

      A typical wastewater project requires between 40 and 50 P&IDs, all of which meet the International Society of Automation (ISA) S5.1, S5.3, S5.4, and S5.5 standards. Smaller facility upgrades or retrofit projects require fewer drawings depending on the extent of process modifications mandated by the project. The documents are typically printed on 28-cm by 43-cm (11-in. by 17-in.) or 56-cm by 86-cm (22-in. by 34-in.) or larger sheets of paper so the lettering is easy to read (see Chapter 4 for more details).

2.1.2.3 Process Control System Architecture Diagram

      The process control system architecture diagram, or system configuration diagram, is a basic drawing of control system components and their locations. The system configuration and communication schematics show all of the process control system’s significant components, including workstations, printers, modems, RTUs, PLCs, interfaces between units, networks, communication media, and communication protocols (see Chapter 4 for a detailed example of a process control system architecture diagram).

2.1.2.4 Elementary Wiring Diagrams

      Elementary wiring diagrams illustrate how a specific piece of equipment will be controlled electrically. The design team should create a separate wiring diagram for each piece of control system equipment. If there are several identical pieces of equipment, one typical drawing can be created with an accompanying chart to identify the respective applicable equipment numbers and any unique characteristics. The diagrams should include selector switches, pushbuttons, lamps, relays, fuses, and field devices (e.g., solenoids and sensors/transmitters for flow, temperature, pressure, level, or other devices with switch outputs that are wired into the circuit) and indicate if contacts are momentary or maintained. Inputs to the control system should be shown for clarity and complete identification of required interfaces with other systems (i.e., motor control centers, motor-operated valves, variable-frequency drives [VFDs], digital inputs to PLCs and DCS, etc.). Outputs from the remote control system must be shown in all instances.

2.1.2.5 Instrumentation and Panel Location Drawings

      Instrumentation and panel location drawings should show the physical location of all I&C equipment. They can also be included with electrical-conduit layout drawings or mechanical-equipment layout drawings (in the latter instance, separate electrical drawings should be made based on the mechanical-drawings’ background).

2.1.2.6 Instrumentation Installation Details

      Whether or not instruments will operate properly at a WRRF often depends on how they are installed. Installation drawings show how instruments should be mounted and installed. When creating these drawings, designers should make sure that each instrument will be accessible for maintenance. Designers also should review specific manufacturer installation details for any special requirements that should be included with the drawings. Guides from other industries can also be useful. For example, the American Petroleum Institute provides procedures for installing the more generally used measuring and control instruments and related accessories. Finally, as part of the design process, a schedule of deliverables to the client is required (see Table 3.4 for a typical deliverable schedule for a project design by a consulting engineering firm).

TABLE