1) Derived Tags
It is like Volatile Variable and in separate scan list so that any change in any of element in the expression changes the value of Derived Tag is recalculated.
A derived tag is a tag whose value is the result of an expression. An expression can be simply a tag name, or it can be an equation made up of tag names, mathematical and logical operations, special functions, and If-Then-Else logic. Derived tag calculations are carried out at the FactoryTalk View SE Server (also called the HMI server).
Here’s an example of how a derived tag can be used. Suppose there are five weight sensors on a conveyor belt. The tag database contains one tag for each sensor, so the weight at each point on the conveyor belt is monitored. If the weight at any point is excessive, FactoryTalk View triggers an alarm. However, if no individual sensor detects an excessive weight, but the total of all five sensors is too high, an alarm might be triggered. To handle this case, you could set up a derived tag to sum the weights of all five sensors. Then, if this total, which would be the value of the derived tag, is too high, FactoryTalk View can trigger an alarm.
2) Memory Tags
Storing values in memory
Create HMI memory tags to store values without the need for an attached or accessible device. For example, you can use memory tags to:
• Store the result of a calculation.
• Act as a temporary counter or index.
• Maintain information about the system’s current state, for example, which graphic display was last shown.
A memory tag can be used to store values internally.
About retentive memory tags
By default, the value of an HMI memory tag reverts to the initial value specified for the tag, whenever the HMI server containing the tag is shut down and restarted.
To set up a memory tag to retain the last value it was set to, even after the HMI server is shut down, in the Tags editor, select the Retentive check box for the tag.
A retentive memory tag will always have the last value it had prior to the HMI server shutting down. In other words, the tag’s value will not revert to the initial value specified for the tag.
3) HMI Tags vs 4) Direct reference Tags
---
1) tag name
Name of the tag.
2) expression
Expressions built by tags, if~else conditions, etc.
3) command
Commands like Display, DerivedTagOn, etc.,
4) embedded variable
I think here the embedded variable differs with tags. They are like volatile. And, they are kept in scan list so that their values are updated at run time dynamically, even though currenlty on display. But, tags and all, just once while activating the window, they are updated.
It is like Volatile Variable and in separate scan list so that any change in any of element in the expression changes the value of Derived Tag is recalculated.
A derived tag is a tag whose value is the result of an expression. An expression can be simply a tag name, or it can be an equation made up of tag names, mathematical and logical operations, special functions, and If-Then-Else logic. Derived tag calculations are carried out at the FactoryTalk View SE Server (also called the HMI server).
Here’s an example of how a derived tag can be used. Suppose there are five weight sensors on a conveyor belt. The tag database contains one tag for each sensor, so the weight at each point on the conveyor belt is monitored. If the weight at any point is excessive, FactoryTalk View triggers an alarm. However, if no individual sensor detects an excessive weight, but the total of all five sensors is too high, an alarm might be triggered. To handle this case, you could set up a derived tag to sum the weights of all five sensors. Then, if this total, which would be the value of the derived tag, is too high, FactoryTalk View can trigger an alarm.
2) Memory Tags
Storing values in memory
Create HMI memory tags to store values without the need for an attached or accessible device. For example, you can use memory tags to:
• Store the result of a calculation.
• Act as a temporary counter or index.
• Maintain information about the system’s current state, for example, which graphic display was last shown.
A memory tag can be used to store values internally.
About retentive memory tags
By default, the value of an HMI memory tag reverts to the initial value specified for the tag, whenever the HMI server containing the tag is shut down and restarted.
To set up a memory tag to retain the last value it was set to, even after the HMI server is shut down, in the Tags editor, select the Retentive check box for the tag.
A retentive memory tag will always have the last value it had prior to the HMI server shutting down. In other words, the tag’s value will not revert to the initial value specified for the tag.
3) HMI Tags vs 4) Direct reference Tags
---
1) tag name
Name of the tag.
2) expression
Expressions built by tags, if~else conditions, etc.
3) command
Commands like Display, DerivedTagOn, etc.,
4) embedded variable
I think here the embedded variable differs with tags. They are like volatile. And, they are kept in scan list so that their values are updated at run time dynamically, even though currenlty on display. But, tags and all, just once while activating the window, they are updated.
