Understanding Tags

Working with Tags

Once you have Tags in your Tag Browser, they will automatically start executing. The Designer is live, and you can see your Tags update in real time and write values directly to them. The most commonly used type of tag is an OPC Tag, which gets its value from a device like an OPC Server. You can connect to just about any type of device out there and show the data on screen, as history, and write back whenever you want. Tags make Ignition extremely flexible and easy to show data. See the Quick Start Guide to get some tags created and in your client.

There are many things you can do with Tags to keep everything organized and give you exactly what you need.

• Learn about the different types of Tags
• Organize your Tags
• Set Metadata properties
• Set scaling
• Import/export

Once you have some Tags created, you can edit them to include even more features. You can:

• Set up Alarms
• Store Historical data
• Add Security
• Add Scripting to Tag Events

In addition to all that, Ignition allows you to create UDTs (User Defined Types) out of your Tags to rapidly develop projects with structured objects. This gives you the ability to create a master type then quickly add many instances. UDTs allow you to make a change in one place and see it automatically propagated to every instance. 

What are Tag Providers?

Tag Providers and Drivers

At the highest level of configuration is the Tag Provider. A provider is a tag database (a collection of tags) and a name. An Ignition Gateway can have any number of tag providers, and therefore the name is used to distinguish which provider a tag comes from. Tag Providers can be set up with security or even disabled independent of each other.

Every provider holds tags, but not every provider is a Tag driver, or a tag executor. Some tag providers simply make tags available to use, and the tag execution is performed by a different driving provider elsewhere. For example, the Database Provider is a Tag provider that simply watches a tag database stored in an external database. It does not execute tags, it only monitors the values of the tags present. Somewhere else there is a tag driver such as a Driving Datasource Provider or a legacy FactorySQL that is executing the tags and storing the values to the database.

Realtime vs. Historian Providers

As discussed above, all Tags reside in a tag provider and provide realtime values. Additionally, there is the concept of tag historian providers, which can store and query historical data for tags. Each tag can optionally have a historian provider assigned to it to whom it will report value changes for historical storage.

Realtime Providers

The Tags "tag database", or how Tag's tag configuration is stored, can take a few different forms. For internal Tags, the configuration is stored in the Ignition Gateway. With the database form, Tags are stored in a SQL database, outside of the Ignition Gateway. Finally, Remote Tag Providers allow Tag Providers of one Gateway to be accessed on a different Gateway. The different storage mechanisms have different pro and cons, and so it is a good idea to acquaint yourself with each of them.

Internal Tag Provider

The Internal Tags Provider manages the Tags inside the Ignition Gateway. This is the most common method and is optimized for the best scaling and performance.

It is possible to create multiple internal providers per Gateway. The Tags can be exposed to other Gateways on the network through the Gateway's OPC-UA settings.

Database Tag Providers

There are two types of Database Tags providers in Ignition:

• Tag Consuming Provider
• Tag Driving Provider (provided by the SQL Bridge module)

While these two tag providers used to be referred to as external tag providers, they function in the same way that they used to. The Driving Provider will execute Tags as well as make available Tags driven by other Tag Drivers looking at the same database, such as other Ignition Gateways using the Driving Provider, or legacy FactorySQL installations, whereas the Consuming Provider will only read the Tags and will not write values back to the database..

The primary benefit of database providers is that the data is stored in a central database, and is therefore accessible to other data consuming systems that do not have the capabilities to connect to Ignition's OPC-UA server as an OPC-UA client, yet still require the need to consume realtime Tag information.

The negative side to external providers is that all Tag values must be written to the database and then polled for change, which is a less efficient method than internal provider's method. In other words, the inherent architecture of the external model does not scale as well as the internal provider model. For more information about those tables and how they work, see the External Tag Provider Reference.

Configuring Realtime Providers

Realtime Tags providers are configured in the Gateway's Configure section under Tags > Realtime. After installation, the Ignition Gateway will start with an internal provider defined. You can edit its name and settings by selecting edit to the right of its entry in the table, or create new providers by selecting Create new Realtime Tag Provider below the table.

There are four types of Realtime Tag Providers that you can choose from:

• Standard Tag Provider
• Remote Tag Provider
• Tag Consuming Provider
• Tag Driving Provider
  

Enum Reference

Almost every property in Ignition that is a dropdown list has an enumeration that starts at 0 and counts down the list. Below are the definitions of Tag property selections: