Top  | Previous | Next

Trigger and Handshake Settings

The trigger settings determine when a group will actually execute. They are examined each time the group evaluates (according to the update rate of the group). If they pass, the group will run and perform its action against the database.

 

The trigger settings are the same for all group types. They are found on the second tab (labeled "Trigger"), in the right side of the Transaction Group workspace.

 

Only execute when value have changed (asynchronous trigger)

These settings are evaluated first. If set, the group will examine whether the values in the specified tags have changed, and if not, will exit evaluation.

It is possible to monitor all Run-Always tags in the group, or only specific ones.

 

Execute this group on a trigger

Enables trigger on a specific item in the group. The trigger item can be any Run-Always item, such as an OPC item, SQLTag reference, or an Expression item set to "Run-Always" mode.

 

In addition to the numeric settings that define the trigger, there are several other options:

•Only execute once while trigger is active - The group will only execute once when the trigger goes into an active state, and will not execute again until the trigger goes inactive first. If unselected, the group will execute each time the trigger conditions evaluate to true.
•Reset trigger after execution - If using the ">0" or "=0" trigger modes, the trigger can be set to write an opposite value after the group has executed successfully. This is useful for relaying the execution back to the PLC.
•Prevent trigger caused by group start - If selected, the group will not execute if the trigger is active on the first evaluation of the group. In the course of designing a group, it is common to stop and start it many times, and sometimes it is not desirable to have the group execute as a result of this. Selecting this option will prevent these executions, as well as executions caused by system restarts.

 

Handshake Settings

Group handshakes are also defined on the trigger tab. It is possible to specify both a success and failure handshake. The success handshake will write the specified value to the given item when the group has finished all other triggered execution without error.

 

The failure handshake, on the other hand, will be written when the group execution is cut short due to an error, such as an error writing to the database or an item.