Word Data Point Tag

Introduction

The Word Data Point Tag represents a 16-bit unsigned integer data tag with a range of 0 to 65535.

Configuration Properties

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

Property	Type	Version	Description
DisplayFormat	WSTRING	3.73	The format used to display the tag's value. This property defines how the value of the tag appears in: The DisplayValue property The Tag Status Window See Number Format for information on how to use this property.
NormalColor	STRING	3.1	The value of the Color property when the tag is normal quality.
Units	WSTRING	3.68	The unit of measurement of the tag, for example: Meter Pulse Count.
HistoricEnable	BOOL	2.5	Whether the value of the tag is stored in the Data Historian.
HistoricDataSource	USINT	3.59	The source of historic data samples. Three options are available: Filtered tag value: The value of the tag after applying change filtering. Raw tag value: The value of the tag without any change filtering. Write commands: Write commands sent to the tag. Available only if HistoricEnable is True. For more information see HistoricDataSource Property below.
HistoricOriginFilter	USINT	3.73	A filter to choose which data is stored in the historian based on the data origin. Three options are available: All data: All data is stored. Timestamped data: Only data timestamped at source is stored. Sampled data: Only sampled data is stored. For more information see HistoricOriginFilter Property below.
HistoricSampleInterval	TIME	2.5	The preferred maximum time interval between consecutive values recorded in the history. For information on how this configuration property works, see HistoricSampleInterval Property below.
HistoricSampleCount	UDINT	2.5	The number of samples to retain in the Data Historian. Each historic record requires 14 bytes disk storage. To work out how much disk storage is required for historic data, multiply HistoricSampleCount by 14.
HistoricSignificantChange	UINT	2.5	The amount the tag value must change before a new value is stored in the historian. Available only if: HistoricEnable is True, and HistoricDataSource is set to Filtered tag value For more information see HistoricSignificantChange Property below.
HistoricListRecordLimit	UDINT	3.30	The number of records to show, when selecting Show Historic Data on the Standard Tag Menu. This value provides the row-count parameter to the FETCH FIRST clause for the SQL command. If HistoricListRecordLimit is set to less than 1, the driver rounds the value up to 1. Using very large values may cause the Show Historic Data command to take a long time to complete.
TemporaryTrendInterval	TIME	3.30	The default time interval of the X Axis in a Temporary Plot of this tag. Values less than 5 minutes are automatically rounded up to 5 minutes by the driver.

HistoricDataSource Property

The HistoricDataSource property defines where historic data samples are taken from. There are three options:

Option	Description
Filtered tag value	The historic samples are taken from the data point tag value after change filtering. Only significant changes to the data point tag value are stored in the historian. This is the best option for real measurements.
Raw tag value	The historic data samples are taken directly from the data point tag value. Each update to the tag will create a new historic record. This option can generate a large amount of historic data. For example: For Calculated Word Data Point Tags a new historic data record is added each time the calculation is run. For I/O Word Data Point Tags a new historic data record is added each time the data source is scanned.
Write Commands	The historic data samples are taken from write commands to the data point tag. Each write command will create a new historic record. This option can generate a large amount of historic data. For example: An IEC 61131-3 Program Tag writing to an Internal Word Data Point Tag can create a new historic record on each program run. This is the best option for manually entered data.

Option

Description

Filtered tag value

The historic samples are taken from the data point tag value after change filtering. Only significant changes to the data point tag value are stored in the historian.

This is the best option for real measurements.

Raw tag value

The historic data samples are taken directly from the data point tag value. Each update to the tag will create a new historic record. This option can generate a large amount of historic data. For example:

For Calculated Word Data Point Tags a new historic data record is added each time the calculation is run.
For I/O Word Data Point Tags a new historic data record is added each time the data source is scanned.

Write Commands

The historic data samples are taken from write commands to the data point tag. Each write command will create a new historic record. This option can generate a large amount of historic data. For example:

An IEC 61131-3 Program Tag writing to an Internal Word Data Point Tag can create a new historic record on each program run.

This is the best option for manually entered data.

HistoricOriginFilter Property

A filter to choose which data is stored in the historian based on the data origin. Three options are available:

Option	Description
All data	All data is stored.
Timestamped data	Only data timestamped at source is stored.
Sampled data	Only data sampled by Fernhill SCADA is stored.

The default value of HistoricOriginFilter is All data.

Most data sources provide either Timestamped data or Sampled data data but not both. You should only consider using this configuration property if:

The data source provides both Timestamped data and Sampled data, for example a DNP3 Outstation Tag, and
You only want to store one type of data in the historian, for example Timestamped data.

For most applications you should use the default of All data.

The HistoricOriginFilter property is available when:

HistoricEnable is True, and
HistoricDataSource is set to Filtered tag value or Raw tag value.

HistoricSignificantChange Property

The HistoricSignificantChange property is used to filter out similar values from the historian.

When a new value is obtained from the data source the new value is compared with the previous value stored in the history:

If there is no previous value to compare against, the new value is stored in the history.
If the difference is less than HistoricSignificantChange, the new value is not stored in the history. The most recent value not stored in the history is retained for when there is a significant change.
If the difference is greater than or equal to HistoricSignificantChange:
1. If available, the most recent value not stored in the history is now stored in the history.
2. The new value is stored in the history.

The effect of filtering out similar data values is shown in this diagram:

The effect of change filtering on samples stored in the historian.

The value you choose for HistoricSignificantChange can affect:

The load on the historian. Lower values increase the load, higher values reduce the load.
The accuracy of the trend of the data. Lower values increase accuracy, higher values decrease accuracy.
How quickly a trend of the data is displayed. Lower values result in slower trends, higher values result in faster trends.

For best results, try to set HistoricSignificantChange just above the noise level in the data source.

The HistoricSignificantChange property is available when:

HistoricEnable is True, and
HistoricDataSource is set to Filtered tag value

HistoricSampleInterval Property

The HistoricSampleInterval property adds extra samples to the history when a data point tag value does not change for a long period of time. The extra samples give confidence in the historic data when the source value is constant.

When a new value is obtained from the data source, a new record is added to the history if:

The HistoricSampleInterval has elapsed since the last record was added to the history.

The effect of adding extra samples is shown in this diagram:

The effect of historic sample interval on values stored in the history.

Note: To be effective, HistoricSampleInterval should longer than the interval between new samples from the data source.

The HistoricSampleInterval property is available when:

HistoricEnable is True, and
HistoricDataSource is set to Filtered tag value

Data Properties

The Word Data Point Tag supports the data properties of the Data Point Tag plus these properties:

Property	Type	Description
Value	UINT	The current value of the tag
Color	DWORD	Indicates the state of the tag using color
UpdateReason	USINT	A code to indicate the reason for the last update to the tag.
IsForced	BOOL	Indicates whether the tag has been forced (true), or not forced (false)
UnforcedValue	UINT	The current value of the tag when this tag has been forced to a fixed value
UnforcedQuality	INT	The quality of the current value when this tag has been forced to a fixed value
UnforcedTimestamp	DATE_AND_TIME	The timestamp of the last update when this tag has been forced to a fixed value
UnforcedColor	DWORD	The color of the tag when this tag has been forced to a fixed value
UnforcedUpdateReason	USINT	A code to indicate the reason for the last update to the tag when the tag is forced to a fix value.
TagErrorCode	USINT	The status of the last update to the tag. A non-zero value indicates an error.
DataSourceError	UDINT	A data source specific error code.

Color Property

The Color property provides an indication of the state of the tag using color:

Tag State	Condition	Color Value
The tag is forced	IsForced = True	The ForcedColor defined in the Database Root Tag
The quality is bad	Quality < 192	The BadQualityColor defined in the Database Root Tag
Otherwise		The NormalColor defined above.

UpdateReason and UnforcedUpdateReason Properties

The UpdateReason and UnforcedUpdateReason properties give a reason for the most recent update to the Word Data Point Tag:

Value	Description
0	None: No update has been stored in the tag.
1	Forced Value: The data point tag is set to a fixed value.
2	Configuration error: There is an error in the configuration.
4	Scanned value: The value was obtained from an external source. The timestamp is provided by Fernhill SCADA.
5	Logged value: The value was obtained from an external source. The timestamp is provided by the external source.
6	Loaded value: The value was loaded from the last saved state of the tag database.
7	Initial value: The value was set by the initial value configuration.
8	WriteValue tag command: The value was set the WriteValue Tag Command.
9	WriteValueQuality tag command: The value was set the WriteValueQuality Tag Command.
11	Calculated value: The value is the result of a calculation.
12	Randomly generated value: The value is randomly generated.
13	Device state change: A device state change caused a change of quality.
14	Offline tag update: The value is an update to the tag when the data source is offline.

When the tag is forced to a fixed value: UpdateReason will be Forced value (1) and the actual update reason is stored in UnforcedUpdateReason.

TagErrorCode Property

When the Quality of the tag data is 'Bad', the TagErrorCode property indicates the reason for the error:

ErrorCode	Description
0	No error.
1	The tag is not associated with a valid data source.
2	The data source reference is valid, but the data source has a configuration error.
3	The offset of the tag is outside the boundary of the data source.
4	The data type is String, but the source value is not a valid word.
5	There was an error converting the data.

Tag Commands

A tag command is an action you can trigger on a tag. The Word Data Point Tag supports these tag commands:

Tag Command	Version	Description
ForceValue	1.2	Overrides the tag to show a fixed constant value. If the tag value is from a data source, updates from the data source are placed in a set-aside area. Note: The override is applied to the tag in the Fernhill SCADA database, and not to the data source.
RemoveForce	1.2	Removes any override currently active on the tag. The actual value from the data source is restored from the set-aside area. If there is no override currently active, RemoveForce has no effect.

Relationships to Other Tag Types

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

The Word Data Point Tag is used as a building block for these tag types:

Further Information

Core Tag

To learn about properties common to all tags.

Data Point Tag

To learn about other types of data tag.

Glossary

For the meaning of terms used in Fernhill SCADA.