Page 360 - Programmable Logic Controllers, Fifth Edition - Mobile version

Name: Tank Size: 16 byte(s) in rpm. Installation and maintenance personnel can easily
locate all data associated with the operation of the tank
since all the information is stored together.
Description: Generic Storage Tank Data Type
Creating Tags

There is more than one way to create tags. You may create
Name Data Type Style Description
Level INT Decimal Stores the Level in Inches tags in the tag editor before your program is entered, enter
Pressure DINT Decimal Stores the Pressure in PSIG tag names as you program, or use question marks [?] in
Temp REAL Float The Temperature in F place of tag names and assign the tags later. Figure 15-21
Agitator_Speed DINT Decimal Speed in RPM shows an example of a controller scope base tag created in
the new tag dialog box. When defining tags, the following
information has to be specified:
Figure 15-20 User-defined storage tank structure.
• A tag name, which must begin with an alphabetic
character or an underscore (_). Names can contain
added. Tags of these types are created to store input, out- only alphabetic characters, numeric characters,
put, and configuration data for the module. Input tags or underscores and may be up to 40 characters in
labeled Data contain the actual input bits from the mod- length. They may not have consecutive or trailing
ule. Configuration tags determine the characteristics and underscore characters, are not case sensitive and
operation of the module. The name Local indicates that cannot have spaces in the tag name.
these tags are in the same rack as the processor. The 1 • An optional tag description, which may be up to
indicates that the module occupies slot 1 in the chassis. 120 characters in length.
The letters I and C indicate whether the data are input • The tag type: base, alias, or consumed.
data or configuration data.
A user-defined structure supplements the predefined • The data type, which is obtained from the list of
structures by providing the ability to create custom- predefined or user-defined data types.
defined structures to store and handle data as a group. • The scope in which to create the tag. Your options
Figure 15-20 illustrates a user-defined structure that con- are the controller scope or any one of the existing
tains data for a storage tank. All data relative to the tank program scopes.
are stored together. In the design stage the programmer • The display style to be used when monitoring the
creates a generic user-defined memory structure that con- tag in the programming software. The software will
tains all the different aspects of the storage tank. Each display the choices of available styles.
member has a meaningful name and is created in the ap- • Whether or not you want to make this tag available
propriate data type and style like REAL (floating point) to other controllers and the number of other control-
for temperature and DINT (decimal) for agitator speed lers that can consume the tag.

New Tag
Name: All_Stop OK
Controller controller1 Description: This is the Line Stop pushbutton Cancel
Controller tags input.
New Tag... Ctrl+W
Help
Monitor Tags Tag Type: Base
Edit Tags
Verify Alias
Export Tags... Produced 1 consumers
Consumed
Print Ctrl+P
Data Type: BOOL ··· Configure ···
Scope: Controller1(controller)

Style: Binary

Figure 15-21 Controller scope base tag.
Source: Image Courtesy of Rockwell Automation, Inc.

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