An Internal point is a point that only exists within the master station database—it does not physically exist on the system and is not associated with plant. ClearSCADA supports four types of Internal point:
- Internal Analog point—A point that can be in one of a range of numeric values.
- Internal Digital point—A 1-, 2-, or 3-bit point that can be in one of several fixed states.
- Internal String point—A point that has a text string value, rather than a numeric value.
- Internal Time point—A point that has a date/time value.
ClearSCADA can use Internal points to store data at the server—for instance, to store the resultant data from Historic Calculations, or to store calculation results or apply values to equations within Logic programs. You can also use Internal points to test Logic, simulate plant, or produce prototype designs.
ClearSCADA also supports a special type of internal point that you can use to perform simple calculations on data in the database (see Calculation Points).
Example:
You might write a Logic program that triggers a series of actions should a reservoir reach a particular level.
In order to test out the Logic and check that the necessary actions occur in the right order and have the desired effect, you might create Internal points on your system to simulate a reservoir reaching the crucial level.
By using such Internal points in the Logic program, you can test out the program without affecting the actual plant, and once satisfied that the Logic executes correctly, you can apply the program to the actual points that are associated with the reservoir.
Within Logic programs it is often sufficient to use Variables rather than Internal points. However, Internal points have to be used if the Logic is to provide the additional processing that is associated with points, such as alarm features or historic storage of point values.
The Hand Control pick action enables users to manually set an Internal point’s value. This can be used, for instance, to manually set the value of an Internal point that is being used to simulate plant or test a Logic program. The Hand Control pick action should be disabled if an Internal point value is being set automatically, to stop users from manually hand controlling the point value.
Where a data access application or Logic program sets an Internal point’s value automatically, the application sets the point’s CurrentValue or CurrentState property directly. (The CurrentState property applies to Internal digital points.)
Whenever an Internal point’s CurrentValue or CurrentState property is set directly, ClearSCADA time stamps that value or state with a time of NOW and a Quality of Good, by default. If required, you can force ClearSCADA to time stamp the point value or state with a different time and quality by setting the Internal point’s PresetTimestamp and PresetQuality properties. When the Preset properties are set, ClearSCADA uses the values of those properties to update the point’s CurrentTimestamp and CurrentQuality properties, rather than the defaults of NOW and Good. ClearSCADA also applies the values of the Preset properties to any historic records that it generates.
For ClearSCADA to use the PresetTimestamp and PresetQuality properties when updating an Internal point’s value or state:
- When using automation, write to the PresetQuality and PresetTimestamp properties before the point’s CurrentValue or CurrentState properties.
- When using a Logic program, declare the PresetQuality and PresetTimestamp properties before the CurrentValue or CurrentState properties.
Example:
PROGRAM NewStructuredTextProgram
VAR
TS AT %M(.P.PresetTimestamp) : DATE_AND_TIME;
Q AT %M(.P.PresetQuality) : INT;
V AT %M(.P.CurrentValue) : LREAL;END_VAR;
V := V + 5;
TS := DT#2010-03-02-12:40:00;
Q := 10;END_PROGRAM
In each case, the PresetQuality and PresetTimestamp properties clear whenever the Internal point’s CurrentValue or CurrentState updates. As such, ClearSCADA will only use the Preset properties for the first point update, unless the Preset properties are written to again. If the Preset properties are not set when the point next updates, ClearSCADA will set the point’s CurrentTimestamp to the present time (rather than any offset that may be required) and the point’s CurrentQuality to Good.
You can specify whether ClearSCADA is to log an event each time that an Internal point’s value is set. Where a data access application or Logic program sets the point’s value, the Severity specified for that application is taken into account if the Log Hand Control Events check box is selected for a point.
Example:
If an Internal point’s Log Hand Control Events check box is selected, but the Severity for the Logic program that sets the point’s value is set to ‘None’, ClearSCADA will not log any events to indicate when the point’s value changes.
ATTENTION: Ensure that an Internal point’s Log Hand Control Events check box is clear if an application sets the point’s value on a frequent basis. This is to help prevent the Event Journal from containing numerous events relating to the point’s value being set.
Further Information
Logic Programs: see the ClearSCADA Guide to Logic.
Using Variables: see Using Variables to Store Data Values in the ClearSCADA Guide to Core Configuration.
Historic Calculations: see Configuring Historic Calculations in the ClearSCADA Guide to Core Configuration.
Configuring Internal Analog Points: see Defining Analog Point Details.
Configuring Internal Digital Points: see Defining Digital Point Details.
Configuring Internal String Points: see Defining String Point Details.
Configuring Internal Time Points: see Defining Time Point Details.