The dialog is called in FBD/LD code worksheets by double-clicking on a variable, contact or coil, or by selecting 'Object Properties...' from the context menu of the object.
The 'Variable' dialog is used in FBD/LD code worksheets to
create and insert new local variables and global symbolic variables and to declare them at the same time. The declaration is automatically inserted into the local variables worksheet (in case of a local variable) or in the global variables worksheet (in case of a global symbolic variable), respectively.
Global I/O variables cannot be created this way. A global I/O variable is automatically created in the global variables worksheet when dragging a process data item (i.e., device terminal) from the 'Devices' window into the code. (Process data items are passed from EcoStruxure Machine Expert to EcoStruxure Machine Expert - Safety together with the safety-related device information and data.)
insert variables into the code which have already been declared in a variables worksheet (all scopes).
replace existing variables.
declare FB instances.
insert a constant (literal) into a code worksheet.
display the properties of existing variables.
Each of these procedures is referenced in the related topics list at the end of this page.
NOTE:
The properties of already existing variables cannot be modified using the dialog. For that purpose, you have to edit the declaration directly in the variables worksheet. The dialog can, however, be used to replace a variable in a code worksheet by another already declared variable.
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Dialog element |
Meaning |
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Name |
For a variable: shows the name of the variable for which the dialog was called or which is going to be inserted. For a contact/coil: shows the variable which is assigned to the object or which is going to be assigned. Depending on the selected 'Scope' and 'Group', the combo box contains all local or global variables which are already declared in the variables group. For an FB instance: shows the name of the FB instance or the instance name which is going to be assigned. When declaring a new instance, a default instance name is proposed which you an accept or modify. When selecting an instance name from the combo box, note that the list only contains instances of the same data type (FB type) which are already declared in the POU. EcoStruxure Machine Expert - Safety allows to use DIN qualifiers in IEC 61131 variable names. Rules for using DIN qualifiers According to the IEC 61131 standard, variable names can consist of letters, digits, and underscores. The identifier has to begin with a letter or an underscore. The use of any other character causes the compiler error "Illegal identifier". This naming convention has been expanded in EcoStruxure Machine Expert - Safety in a way that IEC 61131 variable names may also contain DIN qualifiers:
Rules for using DIN qualifiers in IEC 61131 variable names
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Data type |
Specifies the data type of the variable. Data types determine what kind of value a variable can have and define the initial value, range of possible values, and the number of bits. NOTE: The combo box only provides data types for selection which are valid in the current code context, i.e., the list depends on the formal parameter or object selected in the code worksheet. |
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Group |
Shows the variables group within the corresponding variables worksheet (depending on the selected 'Scope') where the variable/FB instance is declared or is used to select the group when declaring a new variable/FB instance. Modifying the group of an already declared variable, i.e., moving a variable by selecting another variables group is not possible. This must be done in the corresponding variables worksheet. |
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Usage |
This combo box is only available for local variables. It specifies the IEC 61131 variable declaration keyword and thus the type of the variable:
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Description |
User-defined comment. The comment entered here is also visible in the tooltip which appears when hovering the mouse over the respective object in the FBD/LD code. |
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Init |
This input field is only available in case of variables. It specifies the initial value of the variable. According to IEC 61131-3 standard, initial values can optionally be assigned to variables. The initial value is applied when processing the variable for the first time during runtime. Rules for initializing variables
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DIAG |
This flag is only available for local output variables (usage VAR_OUT) of the data type WORD. If selected, an implicit diagnostic is performed for this particular variable. Background: Safety-related firmware function blocks as well as user-defined FBs in a safety-related project may have a diagnostic output which allows polling of FB status information. This diagnostic information can be written to a reserved output buffer area (DQ buffer) while compiling and further processed, for example, using a diagnostic tool. To add a local output variable (FB output) to this buffer, the flag 'DIAG' must be selected. |
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Scope |
Specifies the scope of the variable to be inserted/declared. Refer to the topic "IEC 61131 Implementation - Variables" for details.
When declaring and inserting a new variable, the declaration is inserted into the corresponding variables worksheet depending on the activated radio button. Only local variables and global symbolic variables can be declared using the dialog (see notes below concerning global I/O variables). While inserting an already declared variable, the following applies: If 'Local' is activated, the combo box 'Name' contains only the local variables which are declared in the selected group of the local variables worksheet. If 'Global' is marked, all variables are displayed in the combo box 'Name' which are declared in the selected 'Group' of the global variables worksheet. Two different types of global variables are distinguished: Global symbolic variables and global I/O variables. Global I/O variables are assigned to a process data item and cannot be created in EcoStruxure Machine Expert - Safety. Refer to the section "Declaration rules" for details. |
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Object Type |
Only visible for a selected LD object. It is used to specify/modify the object type. You can, for example, replace an NC contact by an NO contact, or select another coil type. Also refer to the related topics list below. |
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Feedback |
If this flag is set, the variable is considered as feedback variable, i.e., it can be used to program an implicit feedback in the safety logic.1 The 'Feedback' flag can only be set in combination with 'Usage = VAR' and 'Scope = Local'. Further Information For further information, refer to topic "Implicit feedbacks in FBD". |
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1 |
When programming implicit feedbacks, the safety logic may be constantly preempted by the updating of the feedback, which may result in a complex timing of your entire application. |
WARNING
UNINTENDED EQUIPMENT OPERATION
Verify the impact of programmed implicit feedbacks particularly with respect to their effect on the performance of your application.
Make certain that suitable organizational measures (according to applicable sector standards) have been taken to avoid hazardous situations if the safety logic application operates in an unintended or incorrect way.
Do not enter the zone of operation while the machine is operating.
Ensure that no other persons can access the zone of operation while the machine is operating.
Observe the regulations given by relevant sector standards while the machine is running in any other operating mode than "operational".
Use appropriate safety interlocks where personnel and/or equipment hazards exist.
Failure to follow these instructions can result in death, serious injury, or equipment damage.
