Database Tags

Introduction

The configuration of database tags influences the behavior and operation of Fernhill SCADA. In this topic we look at:

Tag Types - the different types of database tag.
Tag Folders - how you can organize database tags using folders to reflect plant or equipment structure.
Editing Tags - techniques for editing database tags.
Tag References - managing the references between database tags.
Tag Commands - the commands that can be executed on database tags.

Fernhill SCADA supports a wide range of database tag types. For example:

A Data Point Tag stores a single process value, for example the state of a pump, or a temperature.
An Alarm Tag represents an abnormal condition.
A Graphic Page Tag contains a visual representation of a process or equipment.
A Trend Plot Tag shows how process values vary over time.
A Program Tag runs an IEC 61131-3 program.
A PLC Device Tag represents a programmable logic controller or similar device.
A Channel Tag represents a communication channel to a program logic controller device.

Each tag type is constructed from a number of Tag Components. For example:

All tag types support the properties and tag commands of the common Core Tag.
All tags that raise alarms (abnormal conditions) support the properties and tag commands of the Alarm Tag.

The tag types are described in the Driver Documentation. Each tag type is documented in four sections:

Configuration Properties - The properties that define how the tag operates.
Data Properties - The properties that represent the current state of the tag.
Tag Commands - The commands you can execute on a tag.
Relationship to Other Tag Types - How a tag type builds on the features of other tag types.

A Tag Folder is a container for other tags and folders.

You organize tags using the Tag Window of the Configuration Tool. You can organize tags using folders that best represents a process or equipment.

Icons are used to indicate the type of tag. For example:

The Tag Window supports these editing tools:

Define new tags or folders.
Drag and drop operations to move (or copy) tags or folders.
Rename tags or folders.
Cut, Copy and Paste tags or folders using the clipboard.
Export tags or folders to a file. Import the file back into the same database or a different database.
Backup and restore the entire tag database.

Relationships exist between tags, for example:

Tag references can be absolute or relative:

An absolute tag reference begins with a folder or tag name. The position of the host tag in the database does not change the target of an absolute tag reference.
A relative tag reference always begins with the period character (.). The period character indicates the reference starts with the folder containing the host tag. Use multiple periods to form backward references. A relative tag reference will refer to different tags depending on where the host tag is in the database.

Tag reference examples:

Host Tag	Reference	Target Tag	Comment
FolderA.Tag1	FolderA.Tag2	FolderA.Tag2	Absolute reference
FolderB.Tag1	FolderA.Tag2	FolderA.Tag2	Absolute reference
FolderA.Tag1	.Tag2	FolderA.Tag2	Relative reference to FolderA
FolderB.Tag1	.Tag2	FolderB.Tag2	Relative reference to FolderB
FolderA.Tag1	..FolderA.Tag3	FolderA.Tag3	Relative backward reference

When you rename, or move a tag, the Fernhill SCADA Server will automatically update references in other tags.

You can use the Find References tool to quickly find out which tags refer to a tag.

A Tag Command is a command that you can execute on a tag. For example:

You can execute tag commands from:

Different tag types support different sets of tag commands. Check the Driver Documentation to see which tag types support which tag commands.

To learn about other Fernhill SCADA Concepts.

For the meaning of terms used in Fernhill SCADA.