IEC 62682 defines a large number of terms that are covered by the OPC UA model but not used in the text. These IEC 62682 terms are listed below and include a description, mapping or relationship to OPC UA Alarms and Events:

IEC 62682

OPC UA Mapping / Related Concept

IEC 62682 Definition

OPC UA Application of

absolute alarm

ExclusiveDeviationAlarmType NonExclusiveDeviationAlarmType

An alarm generated when the alarm set point is exceeded.

Both OPC UA models expose a set point and process the Alarm as an absolute Alarm requires, the only difference is the interaction between relative states (High, HighHigh...)

adaptive alarm

Alarm for which the setpoint is changed by an algorithm (e.g., rate based).

In OPC UA adaptive alarming may be part of a vendor specific alarm application, but it would or could make use of a number of standard Alarm functions described in this specification. OPC UA provides limit, rate of change and deviation alarming. Vendors can easily develop algorithms to adjust any of the limits that are exposed.

adjustable alarm / operator-set alarm

ExclusiveLimitAlarmType NonExclusiveLimitAlarmType

An alarm for which the set point can be changed manually by the Operator.

Both OPC UA models allow Alarm limits to be writeable and allow for an Operator to change the limit. For all changes to limits an audit event should be generated tracking the change.

advanced alarming

A collection of techniques that can help manage annunciations during specific situations.

In OPC UA advanced alarming may be part of a vendor specific alarm application, but it would or could make use of a number of standard Alarm functions described in this specification, such as adaptive setting of a setpoint for deviation Alarm. It might also require the definition of new Alarm sub-types.

Annunciation / Alarm Annunciation


A function of the alarm system is to call the attention of the Operator to an alarm.

OPC UA provides an Alarm model that includes concepts such as re-alarming, Alarm silence and Alarm delays, but it is up to the Client application to make use of these features to generate both audible and visual annunciation to the Operator. OPC UA does not provide visual indication but it does provide priority information on which the client can be configured to provide the appropriate visual display. A key concept for alarm display is the concept of Alarm states and a Retain bit (see Annex B for more details).

alarm attribute

Various Alarm Properties

The setting for an alarm within the process control system.

OPC UA defines a number of Properties that reflect what would be termed alarm attributes in IEC 62682 such as Alarm setpoint which maps to the setpoint property in an ExclusiveDeviationAlarmType.

alarm class



A group of alarms with a common set of alarm management requirements (e.g., testing, training, monitoring, and audit requirements).

OPC UA provides ConditionClasses, but also provides other groupings, like ConditionSubClass OPC UA also specifies a number of predefined classes, but it is expected that vendors, other standards group or even end users will define their own extensions to these classes. The OPC concepts allow Alarms to be categorized as needed.

alarm Deadband

ExclusiveDeviationAlarmType NonExclusiveDeviationAlarmType

A change in signal from the alarm setpoint necessary for the alarm to return to normal.

In OPC UA, an alarm Deadband is optionally provided for all limit based alarms. It provides the same functionality as described in IEC 62682


Event Subscription

A function which selects alarm records to be displayed according to a given element of the alarm record.

In OPC UA Alarms are received by a Client according to the specific filter requested by the Client. The filtering can be very robust or very simple according to the needs of the client. It is up to the Client application to generate and provide the appropriate filter to the server. OPC UA’s Alarm model is a subscription based model, not a push model that is configured on a server. The choice of filter is a client’s responsibility.

alarm flood

Alarm diagnostics

A condition during which the Alarm rate is greater than the Operator can effectively manage - (e.g., more than 10 Alarms per 10 minutes).

OPC UA does not define Alarm flooding but it does provide the capability to collect diagnostics that would allow an engineer to review overall Alarm performance.

alarm group

alarm group

A set of alarms with common association (e.g., process unit, process area, equipment set, or service). Alarm groups are primarily used for display purposes.

OPC UA allows the definition of Alarm groups and the assignment of Alarms to these groups. In addition. OPC UA allows Alarms to also be part of a category. OPC UA also allows Alarms to be organized as a HasNotifier hierarchy (see clause 6). Groups, categories and hierarchies can be used for filtering or restricting Alarms that are being displayed.

alarm history

historical events

long term repository for alarm records.

10000-11 describes historical Events.

alarm log

short term repository for alarm records.

This part does not specify repositories for Alarms. Alarm logging is a Client function.

alarm management

alarm system management

collection of processes and practices for determining, documenting, designing, operating, monitoring, and maintaining alarm systems.

OPC UA provides an infrastructure to allow vendors and Operators to provide Alarm management, as such it should be an integral part of an alarm management system.

alarm message


text string displayed with the alarm indication that provides additional information to the Operator (e.g., Operator action).

OPC UA provides an Event structure that includes many different pieces of information (see 10000-5 for additional details). Clients can subscribe for as much of this information as desired and display this as an Alarm message. All typical fields that would be associated with an Alarm message are available. In addition, OPC UA provides significant additional information.

alarm priority


relative importance assigned to an alarm within the alarm system to indicate the urgency of response (e.g., seriousness of consequences and allowable response time)

OPC UA provides a Priority Variable as part of the Alarm Object that provides the same functionality

alarm rate

Alarm diagnostics

the number of alarm annunciation, per Operator, in a specific time interval.

OPC UA provides diagnostics allowing the collection of Alarm rate information at any level in the system.

Record (Alarm)

Events, Event filtering

a set of information which documents an alarm state change.

In OPC UA all Alarms are generated as an Event and the Client can select the fields that are to be included in the Events. This selection can be customized for each AlarmConditionType, which allows a customized Alarm record to be generated.

alarm setpoint, alarm limit, alarm trip point

Limit Alarms, Discrete Alarms

the threshold value of a process variable or discrete state that triggers the alarm indication.

OPC UA supports Alarm limits and setpoints for multiple Alarm types, including limit Alarms and discrete Alarms.

Sorting (alarm)

a function which orders alarm records to be displayed according to a given element of alarm record.

OPC UA does not provide Alarm sorting as part of an event subscription. Multiple filtering options are provided, but the Client is required to perform any ordering of Alarms.

alarm summary, alarm list

a display that lists alarm annunciations with selected information (e.g., date, time, priority, and alarm type).

In OPC UA Alarm summaries and Alarm lists are Client functionality and are not specified. Extensive filtering capabilities are provided by the Server to allow easier implementation of Alarm summaries or lists by a Client.


An audible and/or visible means of indicating to the Operator an equipment or process condition that can require evaluation when time allows.

Alerts are items that should be attended to, but are not as urgent as Alarms. OPC UA does not differentiate between Alarms and alerts, but it does provide a full range of priorities for Alarms. It is up to the end users to determine what range of priorities are considered an alert vs an Alarm etc.

allowable response time

The maximum time between the annunciation of the alarm and when the Operator takes corrective action to avoid the consequence.

OPC UA does not provide any specific fields for allowable response time, but it does track the times at which an Alarm occurs and when any actions are taken on the Alarm.


device or group of devices that call attention to changes in process conditions

OPC UA does not define annunciators, this is Client functionality that can be implemented using OPC UA


comprehensive assessment that includes the evaluation of alarm system performance and the effectiveness of the work practices used to administer the alarm system.

OPC UA does provide a number of features that can facilitate an audit, including diagnostics and audit events. Do not confuse OPC Audit Event with the IEC audit concept.

bad-measurement alarm

an alarm generated when the signal for a process measurement is outside the expected range (e.g., 3.8 mA for a 4 mA to 20 mA signal).

A bad measurement Alarm is not defined in OPC UA, but limit Alarms are defined and they could be used directly to represent a bad-measurement Alarm. Alternatively, limit Alarms could be further subtyped to allow easier filtering on bad-measurement Alarms if desired.

bit-pattern alarm

Discrete alarm

an alarm that is generated when a pattern of digital signals matches a predetermined pattern.

In OPC UA a bit pattern Alarm can be mapped to a DiscreteAlarmType.

calculated alarm

An alarm generated from a calculated value instead of a direct process measurement.

In OPC UA any of the defined Alarm types can be applied to calculated values or to process values.

call-out alarm

alarm that notifies and informs an Operator by means other than, or in addition to, a console display (e.g., pager or telephone)

OPC UA does not specify call-out alarms, since this is client functionality. OPC UA does provide the ability to categorize or group an Alarm such that it could be easily identified as requiring a different type of annunciation.

chattering alarm

OnDelay, OffDelay

alarm that repeatedly transitions between the alarm state and the normal state in a short period of time.

The OPC UA features of OnDelay and OffDelay can be used to help control chattering Alarms.



the process of separating alarms into alarm classes based on common requirements (e.g. testing, training, monitoring, and auditing requirements).

OPC defines a number of extensible ConditionClasses that can be used for this purpose.

controller-output alarm

alarm generated from the output signal of a control algorithm (e.g., PID controller) instead of a direct process measurement.

OPC UA does not provide an Alarm type for controller-output alarm, but a type could be created or an existing type could be used, depending on the requirements.

dynamic alarming

An automatic modification of alarm attributes based on process state or conditions.

OPC UA does not define dynamic alarming behaviour, but it allows programmatic access to limits, set points or other parameters that would be required for a dynamic alarming solution.


enhanced alarming technique that can verify and restore alarm attributes in the control system to the values in the master alarm database.

OPC UA does not provide enforcement, but it enables enforcement by providing an information model that includes default setting for Alarm types as well as original settings for dynamic Alarms. These features can be used by a Client application to provide enforcement.

fleeting alarm

Suppression, Shelving

An alarm that transitions between an active alarm state and an inactive alarm state in a short period of time.

OPC UA provides Alarm Suppression and Shelving which an Operator might use to control fleeting Alarms.

first-out alarm

first-up alarm



An alarm determined (i.e., by first-out logic) to be the first, in a multiple-alarm scenario.

OPC UA can support first-up/first-out Alarms as part of the Alarm information model, including definition of the group of Alarms.

instrument diagnostic alarm


An alarm generated by a field device to indicate a fault (e.g., sensor failure).

OPC UA provides support for InstrumentDiagnostic Alarms that can be used to represent a failed sensor or an instrument diagnostic.


Alarm Diagnostics

measurement and reporting of quantitative (objective) aspects of alarm system performance.

OPC UA provides diagnostic collection capabilities that can be used to measure and reports quantitative information related to alarm system performance.

nuisance alarm

Alarm Diagnostics

An alarm that annunciates excessively, unnecessarily, or does not return to normal after the Operator response is taken. EXAMPLE: Chattering alarm, fleeting alarm, or stale alarm.

The OPC UA model provides Alarm Diagnostics for tracking the information needed to identify if an Alarm is a nuisance Alarm (i.e. has been in an Alarm state excessively or does not return to normal).

plant state

plant mode


defined set of operational conditions for a process plant.

OPC UA provides an example StateMachine (see Annex F) that can be customized or adapted to provide process information. This StateMachine could also be used to affect alarming.

process area

Event Hierarchies

Object References (Part 5)

physical, geographical or logical grouping of resources determined by the site.

OPC UA provides multiple manners in which an information model can be displayed, this includes grouping objects into process areas or any other desired grouping. This is an inherent part of the OPC UA information model.

re-alarming alarm, re-triggering alarm



alarm that is automatically re-annunciated to the Operator under certain conditions.

OPC UA supports re-alarming as part of its base AlarmConditionType.

recipe-driven alarm


Alarm Limits

alarm with setpoints that depend on the recipe that is currently being executed.

OPC UA provides support for adjustable Alarm limits. It also provides support for programs and other functionality that could be used to drive recipes. Annex F provides an example of a StateMachine and how it could be used to adjust Alarm settings.


LatchedState / Reset

Operator action that unlatches a latched alarm.

OPC UA provides an optional StateMachine to indicate an Alarm is capable of being latched and is in a latched state. It also provides a Reset Method for clearing the latched state.

safety related alarm

safety alarm


an alarm that is classified as critical to process safety for the protection of human life or the environment.

OPC UA defines a safety ConditionClass for grouping safety related alarms.

stale alarm

Alarm Diagnostics

alarm that remains annunciated for an extended period of time (e.g., 24 hours).

OPC UA Alarm Diagnostics can track the length of time an Alarm is active.

state-based alarm - mode-based alarms


alarm that has attributes modified or is suppressed based on operating states or process conditions.

OPC UA can provide a system state StateMachine to support process, device or system states (see Annex F). With this StateMachine Servers can adjust Alarm attributes or just Suppress or Disable Alarms based on the StateMachine. The StateMachine can be applied at multiple levels in the system.

statistical alarm


alarm generated based on statistical processing of a process variable or variables.

OPC UA provides an Alarm Condition class that any of the existing AlarmConditionTypes can be assigned to. This allows any Alarm types, such as limit Alarms, to be generated by statistical analysis.



Any mechanism to prevent the indication of the alarm to the Operator when the base alarm condition is present (i.e., shelving, suppressed by design, out-of-service).

OPC UA provides a flag SuppressedOrShelved that matches this functionality.

suppressed by design


alarm annunciation to the Operator prevented based on plant state or other conditions.

OPC UA provides a SuppressedState that matches this functionality.

system diagnostic alarm


alarm generated by the control system to indicate a fault within the system hardware, software or components.

OPC UA defines a system diagnostic Alarm that can be used to represent faults with system hardware, software or components.


OPC UA supports enable / Disable of Alarms, which was supported in older version of 18.2 and IEC 62682, but these options are no longer supported and used in either 18.2 or IEC 62682. Servers that wish to be compliant to 18.2 and IEC 62682 should not use Disable / Enable methods defined in this specification.

The following terms in IEC 62682 match the terms/concepts defined in the OPC UA specification and do not need any addition mapping or discussion:

  • Acknowledge
  • Active
  • Alarm
  • Alarm OffDelay
  • Alarm OnDelay
  • Alarm Type
  • Deviation Alarm
  • Discrepancy Alarm
  • Event
  • Highly Managed Alarm
  • LatchingAlarm
  • OutofService
  • Rateofchange alarms
  • Return to normal
  • Shelve
  • Silence
  • Unacknowledged