Distributed Control Systems - Part C

Flashcards on Alarm Management, History Management, Security, Redundancy, Change Management, and Online Changes in Distributed Control Systems.

What is the purpose of alarm management systems in a Distributed Control System (DCS)?

Alarm management systems provide tools that enable the operating team of a process to avoid or minimize the impact of abnormal conditions.

What is the target condition in a process operation?

Optimal operating condition, which provides the highest quality, minimum waste and emissions at the target capacity.

What standard provides guidelines for alarm management in the process industries?

ANSI/ISA-18.2

What key contents are typically included in an alarm philosophy document?

Defines the purpose and objectives of a process plant alarm system, defines terms, outlines responsibilities, defines notification types and alarm states, and establishes design principles.

What activities occur during the identification stage of the alarm lifecycle?

Piping and instrument diagram reviews, process hazard and operations study, layer of protection analysis, failure mode and effects analysis and environmental permits.

What is alarm defined as?

Audible and/or visible means of indicating to the operator that an equipment malfunction, process deviation, or abnormal condition requires a response.

What are the typical three alarm priority levels recommended by the ISA-18.2 standard?

Emergency, high, and low level alarms.

What are some possible alarm states in a DCS?

Normal, unacknowledged, acknowledged, out of service, returned to normal unacknowledged, shelved, and suppressed by design.

What are some typical alarm types included within DCS?

Absolute alarms, deviation alarms, rate of change alarms, controller output alarms, system diagnostic alarms, instrument diagnostic alarms, and calculated alarms.

What are some alarm attributes that are defined in the basic design stage?

Setpoint, deadband, on-delay, and off-delay.

What functionality must the Human Machine Interface (HMI) Provide?

State clearly the alarm state, tag, priority and type, provide the ability for the operator to silence unacknowledged alarms, acknowledge alarms, shelve alarms and to place alarms out of service, provide capability for an alarm summary display, indicate alarms on process displays and assign alarms to a specific operator workstation.

What are the advanced alarm methods available?

Information linking, logic-based alarming, state-based alarming, and model-based alarming.

What activities are involved in the implementation stage of the alarm lifecycle?

Planning, training requirements, testing and validation, and documentation.

What is the operational stage of the alarm lifecycle?

Refresher training and alarm shelving.

What is the maintenance stage of the alarm lifecycle?

Alarm system testing, replacement-in-kind, and repair requirements.

What are the alarm performance metrics specified by the ISA 18.2 standard?

Annunciated alarms per day/hour/ten minutes, percentage of hours containing more than 30 alarms, percentage of time the alarm system is in a flood condition, unauthorized alarm suppression.

What is history management?

Collection, storage, and maintenance of process data.

What information is considered process data?

Real time data, historical data, event data, configuration data.

What are some potential security threats to a Distributed Control System (DCS)?

Remote login, application backdoors, denial of service, macros, viruses, source routing, and boot sequence.

What are the security methods for a DCS?

Firewalls, access privilege security, and workstation environmental security.

What methods do firewalls use to protect the DCS?

Packet filtering, proxy service, stateful inspection, and source routing.

What is the purpose of management of change?

Ensures that changes are authorized and subjected to the evaluation criteria described in the alarm philosophy.

When an alarm requires testing, replacement or repair, what procedures must be detailed?

The procedures must detail the steps for taking the alarm in and out of service, the warnings required by operations that the alarm is out of service, and documentation of the authorization, personnel, date, and results of the maintenance procedure.

Why use Management of Change (MOC) system?

To safeguard the DCS databases by tracking configuration changes, displaying version differences, facilitating rollbacks, creating management reports, tracking SIS modules, and archiving older database versions and graphics.

What are the steps you need to follow before online edits to Distributed Control System (DCS)

Assess all possible scenarios, notify personnel of the change, and upload and save the current configuration for backup.

Name reasons for change to a DCS configuration database

Process modifications, production optimization, plant expansions, enhanced safety measures and implementation of new regulatory or environmental requirements.

DCS has redundant controllers configuration explain.

Redundant controllers. One is active and the other is the standby controller.

What does Fault-tolerant DCS design accomplish?

Fault-tolerant DCS prevents a critical process from going down due to a fault in any one of its critical systems.

What are the categories availability is broadly categorized?

Basic, high and fault-tolerant.

What is forcing used for?

Test and debug your logic, check wiring to an output device or temporarily keep your process functioning when an input device has failed.