Reading Tag Values

System Model > Variable Tags > Refer to Variable Tags > Read a Tag Value

Data received from the field is represented by the Field and Valid tag elements.

The Field element represents the latest tag field data received from the device.
The Valid element represents the last field data which had "Good" quality.

Note: The Valid tag element initially has bad quality. The quality will only become good when the first read request is successfully finished for the tag, which will only occur when the IO device is online and either background polling is enabled, the tag has been subscribed to, or a TagRead has been initiated.

You can access these elements by using a qualified tag reference (a tag referenced by the tag name and the element name, for example 'MyTag.Field'). The following tables describe each of these elements.

Field Tag Element

Reference Syntax	Citect SCADA Data type	Description
TagName.Field	INT REAL STRING	Implied value of Field element
TagName.Field.V	INT REAL STRING	Value
TagName.Field.VT	TIMESTAMP	Timestamp of when the value last changed
TagName.Field.Q	QUALITY	Quality
TagName.Field.QT	TIMESTAMP	Timestamp of when the quality last changed
TagName.Field.T	TIMESTAMP	Timestamp of when the element was last updated

Valid Tag Element

Reference Syntax	Citect SCADA Data type	Description
TagName.Valid	INT REAL STRING	Implied value of Valid element
TagName.Valid.V	INT REAL STRING	Value
TagName.Valid.VT	TIMESTAMP	Timestamp of when the value last changed
TagName.Valid.Q	QUALITY	Quality
TagName.Valid.QT	TIMESTAMP	Timestamp of when the quality last changed
TagName.Valid.T	TIMESTAMP	Timestamp of when the element was last updated

If you determine that the tag value is incorrect because of a sensor or communication becoming inoperative, the tag value may need to be overridden. The Override tag element is used to store the overridden tag value. For further information, refer to Set a Tag to Override Mode.