Distributed Control Systems - Flashcards

Flashcards about the hardware and software components of distributed control systems, as well as how data communicates through these systems.

What is a Distributed Control System (DCS)?

A control system that is functionally integrated, but also consists of subsystems that can be physically separate and remotely located from one another.

What are the advantages of a hierarchical architecture in DCS?

Enables separation of management and control tasks, improves reliability, and leads to improved scalability.

What is scalability in the context of a DCS?

The ability to expand a control system through the addition of more process input/output (I/O) points and subsystems.

What occurs at the Fieldbus/Process Level of a DCS?

Connection to controlled processes to measure variables (e.g., pressure, temperature, flow rates), sense switch positions, and actuate final control elements.

Name three ways to connect field instruments to a DCS.

Wiring to I/O chassis marshalling system, wiring to an electronic marshalling system, or wiring to a linking device.

What is the function of the controller level in a DCS?

Performs basic process control (continuous, sequential, and batch).

What are the three common methods controllers use to communicate with field instruments?

Modular I/O chassis marshalling, electronic marshalling, or through a linking device.

What does an Analog Input (AI) I/O module do?

Converts analog inputs (4-20mA signals) to a digital signal, including scaling to engineering units and some linearization.

What does an Analog Output (AO) I/O module do?

Provides analog output (4-20mA) signals, converting digital control signals to analog.

What is the purpose of electronic marshalling?

Uses individual I/O point modules that connect one process data point to the DCS.

What is the function of the Operations/Engineering Level in a DCS?

Where plant personnel configure, operate, and maintain the control system.

What is the function of the Enterprise Level in a DCS?

Where business management and process control information merge.

Name the four functional categories of networks in a DCS.

Field-level networks, controller networks, operations/engineering networks, and enterprise networks.

What are some common field level networks?

Foundation Fieldbus, DeviceNet, HART, and wireless HART.

What is the purpose of controller networks?

Provide communication between controllers and the I/O of a DCS and enable controller-to-controller communication.

What is the function of operations/engineering networks?

Provide communication between controllers, data servers, operator workstations, and engineering workstations.

What is the function of enterprise networks?

Connect to the control network to provide access to operational DCS information for business planning and remote access.

What are the three software programs or suites that configure a DCS?

Operating system software, control strategy software, and human-machine interface (HMI) software.

What is the purpose of user manager software in a DCS?

Allows you to set up and administrate the users of the DCS, including user names, passwords, and access levels.

What is the purpose of the DCS explorer?

To configure the controllers and their I/O before any control strategy can be programmed.

What is the purpose of database administrator software in a DCS?

To manage the operational database and perform database maintenance.

Name two international electrotechnical commission (IEC) standards for control languages.

IEC: 61131-3 and IEC 61804-2.

According to IEC-61804-2, what must function blocks include?

A function block input and output must include both a value and status attribute, and a must support mode parameters.

What is the function of HMI programming software?

Allows the operators to control the process using a mouse, by touching the screen, or using keystrokes.

What are the three databases in a DCS?

Operational database, historical database, and alarm database.

What is the function of the operational database?

Updates continuously with process information from controllers and changes from an HMI or engineering workstation.

What is a historical database?

A database that updates continuously with process information and stores process variable values and all process events over time.

What is the function of an alarm database?

A database that updates continuously with process alarm information and events.

What determines that required format of a digital signal in data flow

The network protocol .

What is a peer-to-peer network?

A group of computers connected together so they can share resources and information

In a client server network, where do users share and access resources?

The central location where users share and access network resources.

What is a scan cycle?

A single sweep of a digital control systems operation

What is the scan time?

The amount of time it takes for one scan cycle to complete.

What two categories of tasks does a controller in the DCS execute?

Control tasks and maintenance tasks

When does a DCS controller become overloaded?

By requiring it to perform too much control execution and communication processing