Add a Variable Tag

Equipment

The name of the equipment associated with the variable tag. Select a name from the drop-down list of existing equipment definitions, or enter a name.

There is a limit of 254 characters across the Equipment and Item Name fields, including any separating periods (.).

Item Name

The name of the item with which the variable tag is associated.

Items form part of an equipment hierarchy. They can be used to associate tags, alarms and trends with a particular attribute of a physical piece of equipment (see Items).

There is a limit of 254 characters across the Equipment and Item Name, including any separating periods (.).

Note: When entering an item name, avoid using any Reserved Words. If you use any of these, an error message will display when you compile your project.

Tag Name

You can use any name for a tag (79 characters) provided it follows the Tag Name Syntax rules and is not the same as the name of a Cicode function within the project (or any included projects). See Reserved Words for a list of restrictions on naming.

If you have many tags, use a naming convention (see Structured Tag Names). This makes it easier to find and debug your tags. When the tag name is referenced on a graphics page, Cicode, etc., it can be used with or without a specific tag element or item.

If you are using distributed servers, the name needs to be unique to the cluster (for example, you cannot have the same variable tag name in more than one cluster).

Note: Plant SCADA will automatically resolve tags without a cluster context specified if every tag name in the project is unique. See Clusters.

Cluster Name

The name of the cluster that runs the variable tag. This field needs to be defined if your project has more than one cluster.

You can leave this field blank in a multi-cluster system if cluster replication is enabled (see the parameter [General]ClusterReplication).

I/O Device

The name of the I/O device where the variable is stored (31 characters). If using I/O device redundancy, you need to specify the primary I/O device name here, not the standby.

Note: Avoid changing the tag's I/O device name from this FORM as the variable.dbf will not be updated. If you do change the tag's I/O device name you will need to clear the tag's reference fields.

Data Type

The type of I/O device variable (16 characters). I/O devices support several data types that are used to exchange data with Plant SCADA. Because of the lack of an industry standard, many I/O device manufacturers use individual naming conventions for their I/O device variables. However, every variable corresponds to one of the Tag Data Types.

Note: If you do not specify a range for your tag, then an out of range alert message will be generated if you write a value which is outside the range of the type.

You need to specify the correct data type that corresponds to the data type of the I/O device variable you are configuring. Each data type has a unique address format. You need to use this format when you are specifying the address of the variable (as the Address property).

You will want to verify that you only use data types that are valid for your I/O device. If you do not specify a data type, the variable will be treated as 16-bit integer.

Plant SCADA supports concatenation of I/O device registers. For example, you can define a real data type (in Plant SCADA) as two contiguous int data types (in the I/O device). Plant SCADA reads across the boundary of the two INTs and returns a REAL.

If you use concatenation of registers, the address of the variables needs to be on odd boundaries or even boundaries. You cannot mix address boundaries. For example, V1, V3, V5 are valid addresses.

Be careful when using this feature: the I/O device needs to maintain the integrity of the second register. (If the I/O device writes to the second int, the value of the real could be corrupted.) The structure of some I/O devices might not support this feature, and might therefore behave unpredictably.

Address

The register address in the I/O device where the variable is stored (254 characters). The format and prefix of an address will depend on the protocol configured for the I/O device, which can be determined by checking the Protocol field on the I/O devices view in Plant SCADA Studio.

Note: The address of the variables for all I/O devices using the same protocol needs to be on odd boundaries or even boundaries. You cannot mix address boundaries.

Comment

Any useful comment (254 characters).

Deadband

(11 characters). A deadband allows the value of a variable tag to fluctuate within a defined threshold without updates being sent through the system. This may be useful if a tag produces many small, insignificant value changes. The threshold is represented as a percentage of the tag's engineering range. The default value is 0 (zero), which captures every value change.

For example, if a variable tag has an engineering range of zero to 10000, a deadband of 1 would mean a change in value would have to be greater than 100 (or 1 percent of the range) to be recognized. If the current value was 5600, the tag in the PLC would have to change to a value greater than 5700 or less than 5500 before an update would be sent through the system.

The deadband setting for a variable tag will not apply to an associated trend tag. If a trend tag requires a deadband setting, it should be configured independently in the trend tag properties.

Note: Some data types support an engineering range that includes negative values. For example, a two-byte integer has a range of -32,768 to 32,767. In this case, the deadband percentage specified would need to be measured against a possible range of 65535. See the topic Tag Data Types to determine the default range for each of the different data types supported by Plant SCADA.

Eng Units

(8 characters.) The engineering units that the value represents (for example %, deg, mm/sec, etc.). This property is optional. If you do not specify engineering units, no engineering units are used.

Format

(11 characters). The display format of the value (of the variable) when it is displayed on a graphics page, written to a file, or passed to a function (that expects a string). This property is optional. If you do not specify a format, the format defaults to ####.##.

For more information, see Format Specifiers.

Unique ID

A unique ID is applied to each of the variable tags in a Plant SCADA project to provide consistent identification for integration with future software releases. This field is read-only in Plant SCADA Studio.

Each unique IDs is a Globally Unique Identifier (GUID) generated by Plant SCADA using the following format:

XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX

For more information, see Unique IDs for Variable Tags and Equipment.

Note: It is highly recommended that you only use Plant SCADA to generate the unique identifiers for the variables in your system. If for some reason this is not possible, use a reputable tool to generate GUIDs that match the format described above.

If you use an external tool to modify the variables database, the compiler will indicate if a Unique ID is invalid, duplicated or missing.

Raw Zero Scale /
Raw Full Scale

The unscaled (raw) values (of the variable) that represent the zero point and full scale point for the data (11 characters). The raw values are the values that Plant SCADA reads from the I/O device.

Note: If not defined, the Raw Zero Scale and Raw Full Scale will default to the full range based on the data type. See the topic Tag Data Types to determine the default range for each of the different data types supported by Plant SCADA.

Eng Zero Scale /
Eng Full Scale

The scaled values that Plant SCADA calculates from the raw values (11 characters). The Raw Zero Scale is scaled to the Eng Zero Scale and the Raw Full Scale is scaled to the Eng Full Scale. These properties are represented in engineering units and are used as the upper and lower limits of trends and bar graphs.

Many I/O devices return an integer to indicate the value of an analog input. To return a usable value, the I/O device converts an input signal (usually 4-20 mA) to a raw scale variable, usually in the range 6400 to 32000.

To present this variable as a meaningful value, you can specify a scaling calculation. Plant SCADA then scales every value accordingly, as in the following diagram.

The scaled value of the variable (engineering value), not its raw value, is used throughout the system.

The scaling properties are optional. If you do not specify scaling, Eng Zero Scale defaults to Raw Zero Scale, and Eng Full Scale defaults to Raw Full Scale; that is, no scaling occurs.

A value that is below the specified Raw Zero Scale or above the specified Raw Full Scale causes an "Out of Range" alert message in your runtime system.

Custom 1 to Custom 8

A user-defined string can be used for storage of static information. Information contained within custom1...8 can be used for categorization purposes, as such, it does not usually change during runtime.

Write Roles

Used to determine which Roles have write permissions for a variable tag when using an OPC UA or Industrial Graphics client. Only users included in the specified role(s) will be able to send values to a variable tag from a client application.

Use the drop-down menu to select one of the roles configured in your Plant SCADA project, or manually enter a comma-separated list to include multiple roles.

For more information, see Enable Tag Writes for Industrial Graphics Applications.

Historize

This field enables you to automatically historize and publish the specified variable tag in CitectHistorian.

If you set this field to "TRUE", the variable will be included in an automated configuration process within the Historian environment. If you set the field to "FALSE" (or leave it blank), the variable will not be included.

See Integration with Historian.

Project

The project in which the variable tag is configured.