Variable Tags

System Model > Variable Tags | System Model

A variable tag is a label that you can use to reference the current data value for an I/O device register at a specified address.

This has several benefits:

The address in the I/O device is defined only once. If you change the address, you only need to update the variable tag definition.
You can use a tag name that is logical and descriptive.
You can scale the raw data to an appropriate range in the same declaration.

Variable tags are a fundamental component of much of the functionality supported by a Citect SCADA system. For example, you can use variable tags to:

Display production data on a graphics page (see Display Tags on a Page).
Animate objects on a graphics page in response to tag value changes (see Configure Graphics Objects).
Define commands that control equipment and processes (see Define Commands).
Create alarms that monitor variables tags for specific value changes (see Alarms).
Store tag data for trending and analysis (see Trends).

When you define a variable tag, you need to give it a name and specify its data type. The most common variables supported by I/O devices are digital and integer. However, Citect SCADA also supports REAL, STRING, BYTE, BCD, LONG and LONGBCD data types.

Variable tags also support a set of tag elements that provide different views of a tag's data. This includes extended data values, quality validation and timestamp information. You can read and write to tag elements using tag extensions.

You can use the following types of variable tags:

Arrays allow you to use a single variable tag to represent a set of variables are stored in consecutive memory registers on an I/O device.

Local variables allow you to store data in memory when you start your runtime system.
Calculated variables allow you to generate a tag value at runtime that is the result of a Cicode expression.

Note: You can use Cicode to create a tag browsing session at runtime. See Configure Tag Browsing.