WebAccess uses the "Area of Responsibility" concept for control actions. This allows a user to have varying Levels of access in different Areas of the facility. For example, a user may be allowed to change Temperature Setpoints in one area of the facility, but not is another.
Each tag in the WebAccess database is assigned to one Area and given one security Level.
Each User is assigned a security Level for each Area. The default Level is 0 (the lowest).
In order to change the value of a tag, the User's Area and Level must match the Area and Level of the Tag. WebAccess compares the Tag's Area and Level to the user's Level for that Area. If the user is assigned a security Level greater than or equal to the Tag's Level in the same Area, then the change is permitted.
If the user's Level and Area do not match the tag's Area and Level, a Popup Dialog Box will appear prompting the user to Login as a new user.
Figure 8.2Password Dialog Box - Change Tag Value
In a Web Browser, this new log in is temporary and applies only to changing the selected tag this one time. This does not Login the new user name. This enables a "one shot" opportunity to change the selected tag. After the tag is changed, the Area or Level and user login reverts to the original user.
On the local SCADA node, using ViewDAQ this logs in the new User (until Logout or Login as another user).
Users assigned as Administrators, Power Users or General Users can view any tag and any field associated with a tag. Area and Level restrict the ability to change the value of the tag or a tag field.
Restricted Users can only view tags shown on displays assigned to them. Area and Level further restrict what tags they can change. Restricted Users can acknowledge any alarm on displays they can access (in version 2.1).
WebAccess has 31 user defined Areas and 4 special Areas (Local Tag, View Tag, Tag Field and ViewDAQ)
A tag marked as READ ONLY can't be changed by an operator or administrator regardless of level assigned to the tag.
A Tag is assigned a security Level required to change its value and a Tag is assigned to ONE Area. Any user assigned to the same Area as the Tag and with a Level greater or equal to the Tag's Level can change the tag.
Level 127 is administrator level and is required to change Tag Fields (for example, change alarm limits from the point detail). All Tag Fields require Level 127 in order to change them. Examples of Tag Fields include Alarm Limits, Description, SPANHI, SPAN LO, and ENG UNITS.
ViewDAQ applies only to ViewDAQ (the non-web browser version of VIEW). A level of 127 allows an operator to create, modify and save new Display Groups. Any Level less than 127 defines the uses Exit Password Level required to close a ViewDAQ Display Group.