In ClearSCADA, you use a WITS Maximum Point database item to represent a Maximum point in a WITS Field Device. A Maximum point is a virtual analog input point.
The Field Device calculates the maximum value of a particular analog point, over a specific calculation period, and then stores the value in the Maximum point. The Maximum 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 maximum value at the end of each calculation period; the value remains stored in the Maximum point until the end of the next period.
You can create additional Maximum points, each of which stores the maximum value for a different time period. A point can only have one derived point of each type. Therefore, the second Maximum 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 Maximum Point database items have a combination of configuration properties that are:
- Common to many types of point
- Common to DNP3 points
- Specific to WITS Maximum points.
To configure a WITS Maximum Point database item you use the WITS Maximum 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 Maximum 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 Maximum Points)
- Specify the analog point (the parent point) for which the Field Device should calculate the maximum value (see Specify a Parent Point )
- Specify the calculation period for the maximum value (see Calculation Period for the Maximum 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 Maximum 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.