Digital Tags

Help Contents

Introduction

The Digital Data Point Tag Digital tag icon represents a single bit Digital Data Point Tag with two discrete states. For example: On and Off, or Running and Stopped.

Configuration Properties

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

Property Type Version Description
BlinkState0 BOOL 1.0 Whether the visual representation should blink when the tag value is 0 (zero)
ColorState0 DWORD 1.0 The color of the visual representation of the tag when the tag value is 0 (zero). See Color Values for the different ways to configure a color.
TextState0 WSTRING 1.0 The description of the tag when the tag value is 0 (zero)
BlinkState1 BOOL 1.0 Whether the visual representation should blink when the tag value is 1 (one)
ColorState1 DWORD 1.0 The color of the visual representation of the tag when the tag value is 1 (one). See Color Values for the different ways to configure a color.
TextState1 WSTRING 1.0 The description of the tag when the tag value is 1 (one)
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.
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 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:
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:

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:

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

The HistoricOriginFilter property is available when:

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:

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

The HistoricSampleInterval property is available when:

Dynamic Properties

The Digital Data Point Tag supports the dynamic properties of the Data Point Tag plus these properties:

Property Type Description
Value BOOL The current value of the tag
Blink BOOL Whether the visual indication of the tag should blink or not
Color DWORD Indicates the state of the tag using color
StateDesc WSTRING The current description of the tag
StateChangeTime DATE_AND_TIME The timestamp of the last change in state (0 -> 1 or 1 -> 0)
IsForced BOOL Indicates whether the tag has been forced (true), or not forced (false)
UnforcedValue BOOL 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
UnforcedBlink BOOL Whether the visual indication of the tag should blink or not when forced
UnforcedColor DWORD The color of the tag when this tag has been forced to a fixed value
UnforcedStateDesc String The current description of the tag when this tag has been forced to a fixed value
TagErrorCode USINT The status of the last update to the tag's value. 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 StateConditionColor 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
The state is '1' Value = True ColorState1 defined above.
Otherwise ColorState0 defined above.

TagErrorCode Property

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

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

Tag Commands

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

Tag Command Version Description
ForceValue 1.0 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 1.0 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 Digital Data Point Tag builds on the features of these tag types:

The Digital 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.