The Limit Configuration tab allows you to define limit groups and corresponding limit sets and limit bands. The measurements modeled in these limit groups trigger associated quality codes and alarms when values fall into non-normal bands.
Understanding the Limit Groups Table
The Limit Groups table has the following columns:
• The ID column displays the limit group number. This is a non‑editable field that corresponds to the measurement limit_group_id field and is here for reference purposes.
• The Group Name column displays the Limit Group name.
• The Lo Reasonability column displays the lowest value that can be believed as valid for a measurement.
• The Hi Reasonability column displays the highest value that can be believed valid for a measurement.
• The Description column displays the description given to the Limit Group.
Note: If Lo Reasonability and Hi Reasonability are both set to 0, then the limit group does not have reasonability limits.
Buttons
• Add Limit Group...: Displays a dialog box that allows you to add a limit group.
• Edit Limit Group...: Displays a dialog box that allows you to edit the selected limit group.
• Remove Limit Group...: Removes the selected limit group.
• Refresh: Refreshes the entire tab.
• Service Recache: Notifies DDService to reload the new limit groups.
• Export Configuration...: Displays the SQL needed to create the data displayed in this tab.
Note: Limit group IDs need to be unique.
Understanding the Limit Sets Table
The Limit Sets table is displayed when a row is selected in the Limit Groups table. It has the following columns:
• The Set ID column displays the limit set ID.
• The Set Name column displays the limit set name.
• The Type column displays whether this limit set should use the value of the measurement, or a percentage. Percentages are only supported against the amp rating or nominal voltage.
• The Hysteresis column displays the value threshold past the limit needed to exit a non-normal limit band.
Buttons
• Add Limit Set...: Displays a dialog box that allows you to add a limit set for the selected group.
• Edit Limit Set...: Displays a dialog box that allows you to edit the selected limit set.
• Remove Limit Set...: Removes the limit set from the selected group.
Note: A limit set ID can only exist once in a single limit group.
Understanding the Limit Bands Table
The Limit Bands table is displayed when a row is selected in the Limit Set table. It has the following columns:
• The Band ID column displays the limit band ID.
• The Band Name column displays the limit band name.
• The Limit Value column displays the value of this band or the measurement reference that holds the value.
• The Ref Type column indicates the behavior of the limit if the value is a references to a measurement. Valid values are:
• The Description column displays the band description.
• The Enabled column displays whether the band is active.
Buttons
• Add Limit Band...: Displays a dialog box that allows you to add a limit band.
• Edit Limit Band…: Displays the Add/Edit Limit Band dialog box to edit the parameters of the selected Limit Band.
• Remove Limit Band...: Displays a dialog box that will allow you to remove the selected limit band or cancel the action.
Note: A limit band ID can only exist once in a single limit set. The band IDs should have no gaps between them.
Understanding Limits
A limit group can be associated with an analog or digital measurement. If the associated measurements SCADA value exceeds a limit, the following will occur:
• An alarm will be generated indicating the limit has been breached.
• The measurement will be assigned a High(H), Low(L) or Reasonability(R) quality depending on which limit band was breached.
The limit value can be:
• a constant number
• a reference to measurement on another device (Explicit reference)
• a reference to another measurement on the device of the associated analog or digital (Implicit reference)
The Implicit or Explicit reference can be a Soft or Hard reference. For example, for an analog 'A' whose hi limit band value is taken from a reference to another measurement 'R' on the same device:
• If the reference is a Hard reference then each time the SCADA value of 'R' changes, the current limit band state of 'A' will be recalculated.
• If the reference is a Soft reference then the current limit band state of 'A' will only be recalculated if the SCADA value of 'A' changes, at which point it will use the latest value of 'R' when calculating its limit state.
Understanding the Add / Edit Limit Band Dialog Box
The Add / Edit Limit Band dialog box allows you to add or edit a limit band in a limit set. The dialog box has the following fields:
• The Band ID contains the ID of the band. Currently, there are seven pairs of limit bands supported.
• The Description contains a description of the band.
• The Limit Source radio button selection allows you to define the type of limit:
• Value
• Measurement on the same device (Implicit Reference)
• Measurement on another device (Explicit Reference)
If you select the Value limit source, then the following field is available:
• The Limit Value allows you to enter a value for the limit band.
If you select the Measurement on the same device limit source, then the following field is available:
• The Limit Measurement section allows you to select a measurement and whether the reference will be a hard or soft reference.
If you select the Measurement on another device limit source, then the following field is available:
• The Limit Measurement section allows you to select a device, measurement, and whether the reference will be a hard or a soft reference.
• The Limit State allows you to enable or disable the limit band within the set.
• The Device Lookup button is used to search for and select a device using the Select Device dialog box.
• The Unlink Device button is used to clear the Device field.
Buttons
• Save: Save and close the dialog box.
• Cancel: Cancel the operation and close the dialog box.