Iotellect SCADA/HMI Tags

In Iotellect SCADA/HMI, tags represent process values used by SCADA applications.

A process value, such as temperature, pressure, level, flow rate, or rotation angle, may be received from one or more device accounts. A device account represents an external data source configured in Iotellect, for example, a controller, sensor, protocol device, or gateway connection.

Iotellect SCADA/HMI represents source-specific values as device tags and can bind them to digital twin tags. A digital twin tag is a Digital Twin variable used as the SCADA process value of a modeled object.

Operator screens, dashboards, alerts, charts, reports, history, and business logic use digital twin tags. Individual device tags remain available for diagnostics and maintenance.

A digital twin tag can also be used to send a value to the equipment — see Writing Values to Tags.

This approach keeps the operator interface stable. Operators continue to work with one process value, while the system selects the appropriate device tag according to configured quality, availability, and priority rules.

In the Iotellect SCADA/HMI module, tags are implemented using Iotellect variables. The set of tags is defined in a Digital Twin model, and the tags of each Digital Twin are configured on the Tag Tree screen.

Device Tags

A device tag is a source-specific value received from a variable or field of a device account.

Device tags are used as input values to calculate the digital twin tag value. They also provide information about the quality of the value received from the source. This quality can be used for diagnostics and active device tag selection.

Digital Twin Tags

A digital twin tag is a Digital Twin variable that represents a SCADA process value of a modeled object.

Iotellect SCADA/HMI components use digital twin tags instead of device tags to keep screens, dashboards, alerts, charts, reports, history, and business logic independent from the device account that currently provides the value.

Device Tag to Digital Twin Tag Binding

Device tag to digital twin tag binding defines which device tags provide values for a digital twin tag.

One digital twin tag may be bound to one or more device tags. When several device tags are bound to the same digital twin tag, Iotellect SCADA/HMI calculates the digital twin tag value according to configured rules.

The rules may consider device tag quality, availability, timestamp, configured priority, communication state, or other implementation-specific criteria. For example, Iotellect SCADA/HMI can switch to another device tag when the current source loses communication or reports bad quality.

Active Device Tag

The active device tag is the device tag currently used to calculate the digital twin tag value.

The active device tag may change when the current device tag becomes unavailable, reports bad quality, loses communication, or is replaced by a higher-priority device tag according to the configured switch mode.

The digital twin tag name does not change when the active device tag changes. This keeps the operator interface stable.

A change of the active device tag also changes the destination of values written to the tag — see Writing Values to Tags.

The Active Source field on the Tag Properties screen displays the current active device tag.

Writing Values to Tags

Besides delivering process values to the operator, a digital twin tag can carry a value in the opposite direction — to the equipment it represents. An operator sets a new setpoint on a dashboard, and Iotellect SCADA/HMI passes it to the controller. Values written from by scripts, alerts, and scheduled jobs travel the same path.

To enable this, set the Write Mode of the tag to Active Source and mark the source that should accept values as Writable. Iotellect SCADA/HMI writes to whichever source is active at the time, and leaves the remaining sources untouched even when they are writable as well. Because the active source can change, so can the destination of the values.

Iotellect SCADA/HMI does not confirm that the equipment applied the value, so plan for verification where the outcome matters. The Tag Properties screen shows the current value of every source.

If the tag has Write Mode set to Read Only, or if the active source is not marked Writable, Iotellect SCADA/HMI does not send the value to the equipment and reports no error.

Defining Tags in a Digital Twin Model

Tags belong to the Digital Twin model rather than to individual Digital Twins: every tag defined in a model exists in each Digital Twin created from it. One tag represents one process value, such as temperature, pressure, humidity, pump state, valve position, or rotation angle. Since a tag is a Digital Twin variable, defining a tag also creates that variable in the model.

Open the Digital Twins Settings screen with the button of the same name in the sidebar, then add a tag with the Add Tag button. Each row of the table describes one tag:

Column Name

Description

Name

Name of the tag. This is the name of the Digital Twin variable that stores the tag value.

Description

Human-readable description of the tag. This is the description of the corresponding Digital Twin variable.

Data Type

Data type of the tag value.

History Storage Time

Period during which the historical values of the tag are stored.

Switch Mode

Defines how Iotellect SCADA/HMI switches between several sources bound to the same tag. Possible values:

  • Prefer Highest Priority — Iotellect SCADA/HMI uses the available source with the highest priority. If the primary source becomes unavailable, Iotellect SCADA/HMI switches to another available source. When the higher-priority source becomes available again, Iotellect SCADA/HMI can switch back to it.

  • Stay on Active — Iotellect SCADA/HMI keeps using the current active source while it remains available. If the active source fails, Iotellect SCADA/HMI switches to another available source. When the previous source becomes available again, Iotellect SCADA/HMI does not automatically switch back only because that source has a higher priority. In this context, the selected source provides the active device tag.

Write Mode

Defines whether the tag value can be written to a source. Possible values: Read Only — Iotellect SCADA/HMI does not write the tag value to any source. Active Source — Iotellect SCADA/HMI writes the tag value to the active device tag. See Writing Values to Tags.

Alarm Limits

Threshold values used to monitor the digital twin tag value.
When the digital twin tag value crosses a configured alarm limit, the standard alerting mechanism can generate an alert. Possible values:

  • LL — low alarm limit. Indicates that the value is critically low.

  • L — low warning limit. Indicates that the value is below the normal operating range.

  • H — high warning limit. Indicates that the value is above the normal operating range.

  • HH — high alarm limit. Indicates that the value is critically high.

Unit of Measurement

Unit of measurement of the tag value, specified as arbitrary text.

Properties differ in whether each Digital Twin has its own value:

  • Switch Mode, Write Mode, and Alarm Limits have a separate value in each Digital Twin. The model sets the value that a new Digital Twin starts with. This value can then be changed for an individual Digital Twin.

  • Unit of Measurement and History Storage Time have one value for all Digital Twins created from the model.

Changing a property in the model does not affect Digital Twins that already exist. They keep the values they have.

Generating the Digital Twin Hierarchy

An application usually needs a whole tree of modeled objects — sites, production areas, devices, sensors — and building it one object at a time is laborious. Iotellect SCADA/HMI can generate that tree from a description of the object types instead. To start, open the context menu of the Models node in the System Tree and select SCADA/HMI - Hierarchy Generation; the same generation is available from the Application screen after a new application is created, see Getting Started.

On the Business Objects and Digital Twins Hierarchy screen, each row of the Configure Hierarchy table represents one Digital Twin type (model template) and the container for its instances. Digital Twins are created later based on this hierarchy. The Hierarchy Preview panel reflects the structure in real time.

Add a row for each Digital Twin type with the Level button and configure it with the following properties:

Column Name

Description

Object/Twin Container Name

Context name where Digital Twin instances will be created (e.g., factories, areas).

Object/Twin Container Description

Human-readable name of the container.

Object/Twin Type Name

Internal identifier of the Digital Twin type (e.g., factory, area).

Object/Twin Type Description

Display name of the Digital Twin type.

Parent

Defines the parent-child relationship between the types. The top-level types have Root as their parent.

Properties

Tags of the Digital Twin type. The set of properties is the same as on the Digital Twins Settings screen — see Defining Tags in a Digital Twin Model.

After clicking Create, the generated hierarchy appears in the tree on the left. The tree is used to navigate between the Digital Twin models.

Configuring Tags

Tags are configured in the Tag Tree screen. The Tag Tree provides a SCADA-specific view of process values and their bindings. It shows only the objects and values that describe the monitored system, without exposing unrelated service variables, configuration settings, or internal platform resources.

The Tag Tree is based on the Digital Twin hierarchy. Digital Twins and their instances define the object structure displayed in the tree. For example, an Application may contain sites, production areas, devices, sensors, pumps, valves, or other modeled objects. The hierarchy may be created manually or generated.

When a user selects an object in the Tag Tree, Iotellect SCADA/HMI displays the tags associated with this object. Selecting a higher-level object shows tags for the corresponding part of the hierarchy. Selecting a template can be used to view all tags associated with its instances.

The displayed tags come from the model of the Digital Twin and appear automatically. Here, configure them for the selected Digital Twin — above all, their sources. Most columns repeat the tag properties defined in the model, and only some of them can be changed for an individual Digital Twin. Two columns are specific to the Tag Tree:

Column Name

Description

Tag Name

Name of the tag, consisting of the path to the context where the tag is located and the name of the variable associated with the tag.

Sources

Defines where the device tag value comes from. A source points to a device account and the variable that provides the input value (e.g. a Modbus or OPC UA device account).

Two buttons are available in each row of the table:

Icon

Button Name

Description

Tag Properties

Opens a separate screen for one tag.

Configure

Opens the Configuration dialog of the Digital Twin.

Configuring Sources

The Sources property defines which device tag provides a value for the digital twin tag. One digital twin tag may have one or more sources. Several sources are used when the same process value can be received from different devices, controllers, gateways, device accounts, or communication paths.

To open the Sources table, click the cell in the Sources column of the Tag Tree.

To configure a source for a tag, define the following:

Source Property

Description

Source

Device account that provides the device tag value.

Source Variable

Variable from the selected source used as the input value for the digital twin tag.

Source Field

Field of the selected source variable used as the input value.

Writable

Defines whether Iotellect SCADA/HMI can write tag values to this source. See Writing Values to Tags.

Transform Type

Defines how Iotellect SCADA/HMI converts the value between the source and the tag. The conversion is applied both when reading the value from the source and when writing the value to the source. Possible values:

  • Do Not Transform — Iotellect SCADA/HMI reads and writes the value as is.

  • Bit Field — Iotellect SCADA/HMI reads and writes a bit field of the source value. Iotellect SCADA/HMI takes the parameters from Bit Field Settings.

  • Scale — Iotellect SCADA/HMI scales the value. Iotellect SCADA/HMI takes the parameters from Scale Settings.

  • Expression — Iotellect SCADA/HMI uses separate expressions for reading and writing. Iotellect SCADA/HMI takes the expressions from Expressions Settings.

Bit Field Settings

Configuration for bit field transformation. Applies when Transform Type is set to Bit Field:

  • Bit Offset — position of the first bit of the bit field in the source value.

  • Bit Length — number of bits in the bit field. When writing, Iotellect SCADA/HMI changes only the bits of the bit field and keeps the other bits of the source value unchanged.

Scale Settings

Configuration for scale transformation. Applies when Transform Type is set to Scale:

  • Source Min — lower bound of the source value range.

  • Source Max — upper bound of the source value range.

  • Target Min — lower bound of the tag value range.

  • Target Max — upper bound of the tag value range. Iotellect SCADA/HMI applies the reverse scaling automatically when writing the value to the source.

Expressions Settings

Configuration for expression transformation. Applies when Transform Type is set to Expression:

  • Read Expression — expression applied to the value read from the source.

  • Write Expression — expression applied to the value written to the source.

Priority

Defines which source should be preferred when several sources are available. For example, a primary sensor can have a higher priority than a backup sensor.

Source configuration is part of device tag to digital twin tag binding. It defines how source-specific values become the process value used by the Iotellect SCADA/HMI application.

Tag Properties

The Tag Properties screen brings together the configuration of a single tag and its live state: which source is currently active, what each source reports, and whether the tag is in alarm. Open it with the Tag Properties button in the corresponding row of the Tag Tree.

This is the standard screen of the Digital Twin variable that stores the tag value, and tag-specific configuration and diagnostics sit on its Tag Settings tab. Variables describes the other tabs.

The Tag Settings section shows the tag properties, such as: Data Type, Unit of Measurement, Switch Mode, Write Mode, and the LL, L, H, HH alarm limits, all described in Defining Tags in a Digital Twin Model; and the current state of the tag:

Field

Description

Active Source

Current active device tag, that is, the source that provides the tag value.

Alarm State

Current alarm state of the tag, determined by the configured alarm limits.

The Sources section lists all sources of the tag. Use the Add Source button to add a source. Edit existing sources in the same way as in the Sources table — the Priority, Source, Variable, Field, Writable, and Transform columns correspond to the source properties described there. The remaining columns show the current state of each source:

Column Name

Description

Quality

Quality of the value received from this source. Iotellect SCADA/HMI uses it for diagnostics and active device tag selection.

Current Value (Raw)

Value received from the source before the transformation is applied.

Current Value (Converted)

Value obtained after the transformation is applied. This is the value used as the tag value when the source is active.

Last Update

Date and time when the value of this source was last updated.

Viewing and Setting the Tag Value

The Configure button in a row of the Tag Tree opens the standard Configuration dialog of the Digital Twin. The dialog opens on the Tags tab, which lists the tags of the Digital Twin and preselects the tag of the row you used.

The tab shows the current value of the tag and can be used to set a new value manually. A value set here reaches the equipment as described in Writing Values to Tags.

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