I/O Analog Data Point Tag

Introduction

The I/O Analog Data Point Tag Analog Data Point Tag Icon 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 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. This table summarises which tags you can use for the IODataSource field, and the corresponding format of the IOItemName field.

IODataSource	IOItemName
Allen Bradley PLC	A string formatted with the Allen Bradley PLC Data Address Format.
Allen Bradley Register Block	A string formatted with the Allen Bradley PLC Data Address Format.
File Scanner or URL Scanner	For CSV files, the location of the variable in the file using spreadsheet notation, for example B5 represents row 5 and column 2. For JSON files, the result of the JSONata expression.
Idec Micro PLC	A string formatted with the Idec Micro PLC Data Address Format.
Idec Micro Register Block	A string formatted with the Idec Micro PLC Data Address Format.
Mitsubishi Melsec PLC	A string formatted with the Mitsubishi Melsec PLC Data Address Format.
Mitsubishi Melsec Register Block	A string formatted with the Mitsubishi Melsec PLC Data Address Format.
Modbus PLC Device	A string formatted with the Modbus PLC Data Address Format.
Modbus Register Block	A string formatted with the Modbus PLC Data Address Format.
MQTT Connection	A string formatted with the MQTT IOItemName Format.
ODBC Query	The location of the result in the result set using spreadsheet notation, for example B5 represents row 5 and column 2.
Omron PLC using FINS	A string formatted with the Omron PLC Data Address Format.
Omron PLC using Host Link	A string formatted with the Omron PLC Data Address Format.
Omron Register Block	A string formatted with the Omron PLC Data Address Format.
OPC Server Connection	The OPC item name.
Random Generator	A property name of the random generator.
Siemens S7 Ethernet PLC	A string formatted with the Siemens S7 PLC Data Address Format.
Siemens S7 Serial PLC	A string formatted with the Siemens S7 PLC Data Address Format.
Siemens S7 Memory Block	A string formatted with the Siemens S7 PLC Data Address Format.
SNMP Agent	The OID of the variable in the SNMP Agent.

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 (BCD) 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 raw value is scaled into the tag 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)

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:

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.