I/O Analog Data Point Tag

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5. I/O Analog Data Point Tag

Introduction

The I/O Analog Data Point Tag maps a floating point value to an external data source.

Configuration Properties

The I/O Analog Data Point Tag supports the configuration properties of the Analog Data Point Tag plus these properties:

AllowControls

The AllowControls property controls access to the WriteValue Tag Command.

When AllowControls is FALSE, access to the WriteValue Tag Command is blocked. This prevents any user, or program, sending control requests to the data source from this tag. The default value is FALSE to follow security best practice of deny by default.

Even when AllowControls is TRUE, an operator requires the Write User Privilege to send controls to the data source.

For an operator to send a control to the data source, both of these conditions must be true:

• The AllowControls property is TRUE.
• The operator has the Write User Privilege.

IODataSource and IOItemName

The IODataSource field sets the external data source for the tag. The IOItemName field sets the item of data within the data source. The format of the IOItemName field depends on what type of tag is configured in the IODataSource field.

Use this table to see:

• Which tags you can use for the IODataSource field.
• The format of the IOItemName field.

IOItemType

The IOItemType property defines the type of data in the data source. The property supports these options:

RawScaleConversion

The RawScaleConversion property defines how the tag value is scaled from the raw value. The property supports these options:

Linear Scaling

Linear interpolation is used to scale the raw value to Engineering units. The calculation used to convert the raw value to Engineering Units is:

EUValue = MinScale + 
            (RawValue - RawScaleMin) * (MaxScale - MinScale) / (RawScaleMax - RawScaleMin)

When a write operation is performed, the reverse calculation is used to scale Engineering Units back to the raw scale:

RawValue = RawScaleMin + 
            (EUValue - MinScale) * (RawScaleMax - RawScaleMin) / (MaxScale - MinScale)

Square Root Scaling

Square root scaling is a specialized scaling method intended to compensate for non-linear sensors or transducers. The calculation used to convert the raw value to Engineering Units is:

EUValue = MinScale + 
            sqrt(RawValue - RawScaleMin) * (MaxScale - MinScale) / sqrt(RawScaleMax - RawScaleMin)

When a write operation is performed, the reverse calculation is used to scale Engineering Units back to the raw scale:

RawValue = RawScaleMin + 
            square(EUValue - MinScale) * (RawScaleMax - RawScaleMin) / sqrt(MaxScale - MinScale)

Dynamic Properties

The I/O Analog Data Point Tag supports the dynamic properties of the Analog Data Point Tag.

Tag Commands

The I/O Analog Data Point Tag supports tag commands of the Analog Data Point Tag plus these tag commands:

Relationships to Other Tag Types

The I/O Analog Data Point Tag builds on the features of these tag types:

• Analog Data Point Tag
• Data Point Tag
• Core Tag

Further Information

Analog Data Point Tag

To learn about properties common to all analog tags.

Core Driver

To learn about the Core Data Driver.

Glossary

For the meaning of terms used in Fernhill SCADA.

Fernhill SCADA Version 3.75 (20210827.3). Copyright © 2012-2021 Fernhill Software Ltd: All rights reserved.