The Sample Mode is manually triggered

Ignition
1

Sample Mode​

The Sample Mode setting determines how often the Tag History system will check if the tag’s value should be stored to the database using Deadband and Deadband Style settings.

  • On Change - Ignition will check if the value should be stored to the database each time the tag value changes.
  • Periodic - Ignition will check if the value should be stored to the database at a specific rate defined by the Sample Rate property.
  • Tag Group - Ignition will check if the value should be stored to the database at the specific rate defined within the Tag Group selected under the Historical Tag Group property.

Can I trigger B Tag for storage when A Tag value changes?
I'm worried that the A tag changes twice and the B Tag value doesn't change so I only store it once

2

That is the intention of the data history compression.

3

If you need synchronized storage of values, the tag historian is not the right tool. Use a transaction group (SQL Bridge module) or script an insert to your database.