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:

Property	Type	Version	Description
AllowControls	BOOL	3.12	Whether Fernhill SCADA can send controls from this tag to the data source.
IODataSource	Reference	3.12	A reference to the external data source.
IOItemName	WSTRING	3.12	The data item within the external data source.
IOItemType	USINT	3.12	The type of data to read from the data source.
RawScaleConversion	USINT	3.12	What type of conversion to perform (None, Linear, Square Root).
RawScaleMin	LREAL	3.12	For scaled conversions, the minimum raw scale value.
RawScaleMax	LREAL	3.12	For scaled conversions, the maximum raw scale value.

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 and IOItemName properties define which data item the I/O Analog Data Point Tag is associated with:

The IODataSource property sets the data source for the tag.
The IOItemName property sets the "Address" of the data within the data source.

To configure these properties:

Click the browse button ... of the IODataSource property and choose the data source.
Click the browse button ... of the IOItemName property.
Note: The format of the IOItemName property depends on the type of data source chosen.

To understand how the IOItemName property is formatted, see Data Address Format.

IOItemType

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

IOItemType	Value	Description
16-bit unsigned	0	The source is a 16-bit unsigned integer
16-bit signed	1	The source is a 16-bit signed integer
16-bit BCD	2	The source is a 16-bit Binary Coded Decimal number.
32-bit unsigned	3	The source is a 32-bit unsigned integer
32-bit signed	4	The source is a 32-bit signed integer
32-bit BCD	5	The source is a 32-bit Binary Coded Decimal (BCD) number.
32-bit floating point	6	The source is a 32-bit floating point value.
64-bit floating point	7	The source is a 64-bit floating point value.

RawScaleConversion

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

RawScaleConversion	Value	Description
None	0	No scaling is performed. The raw value is written directly to the tag.
Linear	1	Linear scaling is applied.
Square Root	2	Square root scaling is applied.

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)

Data Properties

The I/O Analog Data Point Tag supports the data 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:

Tag Command	Version	Description
WriteValue	3.12	Writes a new value to the data source via the I/O tag.

Relationships to Other Tag Types

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

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.