Variable Tags
- Last UpdatedJul 18, 2023
- 2 minute read
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:
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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.
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You can use a tag name that is logical and descriptive.
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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 Plant SCADA system. For example, you can use variable tags to:
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Display production data on a graphics page (see Display Tags on a Page).
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Animate objects on a graphics page in response to tag value changes (see Configure Graphics Objects).
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Define commands that control equipment and processes (see Interact with Graphics Pages at Runtime).
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Create alarms that monitor variables tags for specific value changes (see Alarms).
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Store tag data for trending and analysis (see Trends).
When you define a variable tag, you need to give it a Tag Names and specify its Tag Data Types. The most common variables supported by I/O devices are digital and integer. However, Plant 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:
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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.
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Local Variables allow you to store data in memory when you start your runtime system.
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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.