In ClearSCADA, you use a WITS Minimum Point database item to represent a Minimum point in a WITS Field Device. A Minimum point is a virtual analog input point.
The Field Device calculates the minimum value of a particular analog point, over a specific calculation period, and then stores the value in the Minimum point. The Minimum point is therefore a derived point - that is, it derives its value from the value of another analog point (the parent point) (see Derived Points in the ClearSCADA Guide to Core Point Configuration). The Field Device only updates the minimum value at the end of each calculation period; the value remains stored in the Minimum point until the end of the next period.
You can create additional Minimum points, each of which stores the minimum value for a different time period. A point can only have one derived point of each type. Therefore, the second Minimum point you create derives from the first, the third derives from the second and so on. Each point's time period must be an exact multiple of the parent point's time period.
WITS Minimum Point database items have a combination of configuration properties that are:
- Common to many types of point
- Common to DNP3 points
- Specific to WITS Minimum points.
To configure a WITS Minimum Point database item, you use the WITS Minimum Point Form.
The Form contains many fields, organized into tabs. Some of these tabs are common to many types of database item (see Tabs on Point Forms in the ClearSCADA Guide to Advanced Drivers).
NOTE: This point is a type of analog point. Therefore, you can find information about the common functionality for this point in the Analog Points sections of the ClearSCADA Guide to Core Point Configuration. Some of the links below refer you to the relevant sections in that guide.
The Minimum tab contains properties that are specific to WITS. Use the fields on the tab to:
- Configure the point's General Properties (see General Point Properties - WITS Minimum Points)
- Specify the analog point (the parent point) for which the Field Device should calculate the minimum value (see Specify a Parent Point )
- Specify the calculation period for the minimum value (see Calculation Period for the Minimum Value)
- Configure the point's Scanning State Properties (see Scanning States for WITS Database Points)
- Configure the point's DNP3 Object Flag Options (see DNP3 Object Flag Actions)
- Configure the point's Override Properties (see Define whether an Analog Point can be Overridden in the ClearSCADA Guide to Core Point Configuration)
- Configure the point's Trend Properties (see Trend Settings for WITS Minimum Points)
- Configure the point's Logged Data Properties (see Logged Data for WITS Database Points)
- Configure the point's Historic Data Filter Properties (see Historic Data Filter for WITS Database Points).
When you have completed the point's configuration, you need to download the configuration to the Field Device by using the Outstation database item's Download Configuration (WITS Outstation) action.
If your Field Device does not support configuration download, you will need to make the same changes to the Field Device's configuration locally.