What is a Variable

A variable is a programming concept that is associated with something that holds a value or set of values. Typically a variable is defined by a name (set-point, status, etc) and a data type (floating point, Boolean, structure of values).

Background on the Variable Value Change Capability

Schema Viewer is primarily a read-only application for schema programs intended for use by operators who typically may need to interact with a device, but not create the program for it. But, there are occasions where the plant operator needs to adjust parameters in the program. For example, it may be useful for the some subset of plant operators to be able change the initial value for a setpoint variable. Also, it may be useful for another subset of operators to be able to change variables associated with the tuning of a PID loop. These subset of operator can have a mix of users with the ability to change one or both of the variables.

The device programmer (using Design Pad) is able to create a list of Roles (chief engineer, plant operator, etc.), give those Roles Rights (administer security, change Schema Viewer Variables, etc.), and associate Roles with defined Users. In addition, the device programmer can indicate if a particular Role has the ability to change one or more variables.

Accessing the Variable Settings Screens

Access to variable setting is made in one of three variable setting screens: Local, Module, or Global Variable Settings. To access the Global Variable Settings, right-click on the hardware interface face and select Global Variable Settings. For multi-processor products like Chameleon, right-clicking on any device in the node and selecting Global Variable Settings will result in the same dialog. To access the Module Variable Settings, right-click on the hardware interface face and select Module Variable Settings. To access the Local Variable Settings, right-click on white space in a schema and select Local Variable Settings. The figure below shows an example (Module) Variable Settings dialog.

Module Variable Settings Manipulation Dialog

The dialog displays the type and name of each variable.

The Initial Value may be set to a specific number or state. This value is used when the controller starts from power up or the Schema is instructed to reset on download.
The Schema Viewer Users column indicates the Security Role (see the section on Security for more information) that has the right to change the initial value of the variable in Schema Viewer. If a Security User is logged in to Schema Viewer (or there is no one logged in) who does not have this Role then they will not be able to set the initial value. If the User logged in to Schema Viewer is a member of this Role, then they can change the initial value and save the schema with the new initial value setting.

Changing a Variables Initial Value

Use the following steps in Schema Viewer to change the initial value of a variable which has the Schema Viewer Users field set to a role which you are a member of:

1. In the File menu, select Log In. Type your user name and password. Notice that the Schema Viewer application title bar will show the user name currently logged in.
2. Access the desired Variable Settings (as described above).
3. Change the initial value of the desired variable. Boolean type variables use a check-box. Floating point variables use a number field.
4. Select OK to accept the changes.
5. To save changes, press the image of the disk in the toolbar.