String Data Point Tag

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5. String Data Point Tag

Introduction

The String Data Point Tag represents a variable length String Data Point Tag with a maximum length of 160 characters.

Configuration Properties

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

HistoricDataSource Property

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

HistoricOriginFilter Property

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

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.

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 historical 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.

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 String Data Point Tag supports the data properties of the Data Point Tag plus these properties:

Color Property

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

UpdateReason and UnforcedUpdateReason Properties

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

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:

Tag Commands

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

Access from IEC 61131-3 Code

To access a String Data Point Tag from IEC 61131-3 code, use this type of declaration:

VAR
    Variable AT %"Full Tag Name" : WSTRING[1024];
END_VAR

Relationships to Other Tag Types

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

• Data Point Tag
• Core Tag

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

• Calculated String Data Point Tag
• I/O String Data Point Tag
• Internal String Data Point Tag

Further Information

To learn about properties common to all tags.

To learn about other types of data tag.

Glossary

For the meaning of terms used in Fernhill SCADA.

Fernhill SCADA Version 3.95 (20230529.2). Copyright © 2012-2023 Fernhill Software Ltd: All rights reserved.