HMI tags

Use the HMI tag database to define data that
FactoryTalk View
 monitors. There is one HMI tag database per HMI server. Each entry in the database is called an HMI tag. An HMI tag is a logical name for a variable in a device or in local memory (RAM). Each HMI tag is referenced in the HMI tag database.
All parts of the system use tag values.
Graphics
 uses tag values to control the animation in a display or update a trend graph.
Data Log
stores tag values to create a historical record.
HMI tags are required when you need extra information included with the tag value. This extra information can be minimum/maximum value range, value units, or security information. If you do not need this information, you can use direct references to tags in other data servers.
HMI tags you can create
There are three types of HMI tags that you can create. These types are based on the data that they can store. They are:
  • Analog tags
     - store a range of values. These tags can represent variable states such as temperature or the position of rotary controls.
  • Digital tags
     - store two states. Zero will be written as False and any non-zero number will be written as True. Use digital tags to represent devices that can only be on or off, such as switches, contacts, and relays.
  • String tags
     - store an ASCII string, series of characters, or whole words (maximum 82 characters). These tags can represent devices that use text, such as a bar code scanner which uses an alphanumeric product code.
Data sources for HMI tags
When you create an HMI tag you must specify what its data source will be at runtime. A data source can be:
  • Device
     - receives its data from a network device or from another Windows program through a DDE or an OPC server.
    The current value for an HMI tag with a device data source is stored in the HMI server's computer memory in a value table. When the value in the device changes, the value table is updated.
  • Memory
     - data comes only from the value table, rather than a network device or another program.
HMI tags you do not create
When you create a new HMI project,
FactoryTalk View Studio
 creates system tags. They are in a folder called
system
 and have System as their data source. They store information that is generated while the system is running. You cannot create or edit system tags, but you can use them wherever you would use any other tag.
  • System tags
     - store information generated while the system is running, including communication status, system time and date, and so on. There are analog, digital, and string system tags. You can use them anywhere you use other types of tags, but you cannot edit system tags.
Remarks
A graphic display can contain up to a total of 3,000 connections, whether they originate from the expressions or the tags.
  • Each expression associated with an object is counted as one connection, regardless of the number of tags in the expression.
  • Each animation of an object (except the
    Touch
     animation) is counted as one connection.
  • Each connection in the
    Connections
     property of an object that is linked to a tag is counted as one connection.
  • Each pen configured in a
    Trend
     object is counted as one connection.
  • Duplicate references of the same expression or tag connection are counted as the additional connections. For example, one display can contain up to 3,000 numeric inputs, even if all numeric input objects refer to the same tag.
  • Tags associated with embedded variables do not count towards the limit.
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