Calculated Analog Data Point Tag

Help Contents

Introduction

The Calculated Analog Data Point Tag Analog Data Point Tag Icon maps a floating point value to the result of a calculation. The calculation can run:

Configuration Properties

The Calculated Analog Data Point Tag supports the configuration properties of the Analog Data Point Tag plus these properties:

Property Type Version Description
UpdateInterval TIME 1.0 The interval between each calculation. A value of zero (T#0s) disables periodic calculation. See Interval and Offset for information on how timed activities are scheduled.
UpdateOffset TIME 1.0 The offset added to the UpdateInterval to get the actual update time. See Interval and Offset for information on how timed activities are scheduled.
InstructionLimit UDINT 1.0 The maximum number of instructions to execute.

The Calculated Analog Data Point Tag evaluates a calculation at the periodic interval defined by the UpdateInterval and UpdateOffset properties. The result of the calculation is written to the tag. Setting UpdateInterval to T#0s disables periodic calculation.

Calculation

The value of the Calculated Analog tag is defined using an IEC 61131-3 Expression.

To edit the calculation, right-click the tag in the Tag Window, and then click Edit Calculation. The calculation is edited using a Program Code Editor.

Dynamic Properties

The Calculated Analog Data Point Tag supports the dynamic properties of the Analog Data Point Tag plus these additional properties:

PropertyTypeDescription
ExecErrorCode DINT The result of the execution. A value of zero shows success. A non-zero value shows an error occurred.
ExecErrorLocation DWORD The address of the instruction that caused the error. Zero if there was no error.
ExecInstructionCount UDINT The number of instructions processed by the program during the latest execution.
ErrorMessage WSTRING The execution error message. An empty string shows no error.
UpdateTimer TimerStatus The status of the calculation update timer.

Tag Commands

The Calculated Analog Data Point Tag supports tag commands of the Analog Data Point Tag plus these tag commands:

Tag CommandVersionDescription
Run 1.0 Evaluates the expression and writes the resulting value to the tag.

Example configuration

PropertyValue
UpdateInterval1s
UpdateOffset0s
Calculation%"Main.Voltage.Value" * %"Main.Current.Value"

Relationships to Other Tag Types

The Calculated Analog Data Point Tag builds on the features of these tag types:

Further Information

Interval and Offset

To learn how activities are scheduled using Interval and Offset.

Expressions

To learn about the expressions that can used in the Calculation property.

Analog Data Point Tag

To learn about properties common to all analog tags.

Core Data Driver

To learn about the Core Driver.

Glossary

For the meaning of terms used in Fernhill SCADA.