HMI tags

• An external tag is bound to a connection and corresponds to an address in a PLC or another device. Live reads the value from the device and sends written values to it.
• An internal tag has no connection and no address. Its value lives only inside Live: a recipe name, a batch number, an intermediate calculation.

Tags are defined in the HMI Tags section of the project tree. The sections tabs are Tags, Structure Instances, Structures (UDT) and Scaling and Quality.

The table can be grouped: you organize tags with the Group column and the folders in the project tree. The color bar above the table lists each connection as a pill; clicking a pill filters the table to the tags of that connection.

Analog inputs usually sit in the PLC as raw numbers: a range such as 0 – 27648 on Siemens. The operator should see °C, bar or %, not this number. The Scaling and Quality tab does this conversion once, at tag level.

Scaling applies only to external, numeric tags. Objects, trend and archive, alarms, reports, scripts and browser monitoring all use the scaled value of the tag.

Formula: engineering = eng. low + (raw − raw low) × (eng. high − eng. low) / (raw high − raw low). If raw 0 – 27648 is converted to 0 – 100, the value 13824 becomes 50. The engineering value the operator writes is inverted and sent to the PLC as a raw value.

A PLC tag has bad quality while the connection is down, before the first read, or on a read error. An object bound to a bad-quality tag is drawn faded and gray, and a numeric field shows ####. With Use fallback value on, objects and scripts see the fallback value instead of ####.

A plant has dozens of devices with the same structure: every pump has running, fault, speed, current and pressure values. Instead of writing separate tags and addresses for each, you define the structure (the member list) once and add one structure instance per device: name, connection and base address.

Studio generates tags such as Pompa_P101.Hiz and their addresses for each instance. Generated tags are recognized by the STRUCT badge in the table and bind to screen objects and alarms like any other tag. On Siemens S7 the base address is given as DB30; member addresses are calculated from byte and bit offsets.

You can export many tags to Excel (.xlsx) or CSV, edit them, or fill in the template and import it. Excel does not need to be installed. The commands are in the Tools menu and in the toolbar of the table.

• The template contains the column headers, drop-down lists for Connection and Data type, and a Description sheet that explains each column.
• A preview opens before the import: new, to be updated, unchanged, faulty and skipped rows are counted separately. The reason for a faulty row is in the Description column.
• The match key is the Name column: a tag with the same name is updated, a missing one is added.
• The whole operation is a single undo step; Ctrl + Z reverses it all.

A cycle is a record with a name and a duration. Instead of writing the duration everywhere, you define it once in the Cycles table; tags, archives, tasks and screens choose it by name. A new project comes with these cycles: On change, 100 ms, 250 ms, 500 ms, 1 s, 2 s, 5 s, 10 s and 1 min.

• The duration can be 0 (on change) or 20 ms – 24 hours.
• Live applies a read cycle of at least 100 ms for PLC and simulator tags.
• Only changed values are passed to the screens, in batches at most every 100 ms per connection.
• A tag with no cycle selected is read every 1 s.