Rockwell Automation FactoryTalk View Machine Edition Users Guide - Manual (Page 88)

F ACTORY T ALK V IEW M ACHINE E DITION U SER ’ S G UIDE
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For more information, see Chapter 5.
3. In graphic displays, data log models, or anywhere else you want to use a tag’s value,
create a direct reference to the tag. At run time, the tag’s value is passed to the graphic
display or data log model.
When to use HMI tags
Use HMI tags to manipulate tag data and to store tag values in the run-time computer’s
memory.
Scale, offset, or provide a range for data
Use HMI tags if the data server you are using does not provide for:
 Scale or offset a value.
 Set minimum or maximum limits on a value (that is, providing a range of values).
Scale and offset
The scale and offset modify the raw data that comes from and goes to the programmable
controller before the data is saved in the computer’s memory (called the value table). The
scale and offset also modify the value specified in FactoryTalk View before it is written to
the programmable controller.
The scale is a multiplication factor—the value from the programmable controller is
multiplied by the scale.
The offset is a fixed value—after the value from the programmable controller is
multiplied by the scale, the offset amount is added.
Minimum and maximum
HMI tags allow you to set a minimum and maximum value that can be written to the
programmable controller or server.
These values do not affect what is read from the programmable controller or server.
For example, if you specify a minimum of 0 and a maximum of 100, FactoryTalk View
would be able to read a value of 200 from a programmable controller and store it in the
value table, but would not be able to write this value to the programmable controller.
For more information about minimum and maximum, and scale and offset, see Help.
Store values in FactoryTalk View memory
A memory tag can be used to store values without the need for an attached or accessible
device.
For example, you might need to store a value in memory: