The I/O Analog Data Point Tag
maps a floating point value to an external data source.
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. |
OutOfService | BOOL | 3.92 | Whether retrieval of data from the external data source is suspended for this data point tag. |
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. |
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 IODataSource and IOItemName properties define which data item the I/O Analog Data Point Tag is associated with:
To configure these properties:
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.
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. |
Use the OutOfService property to suspend retrieval of data from the external data source.
For normal operation, OutOfService should be set to False. If a data source is providing faulty data, it might be appropriate to set OutOfService to True.
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 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 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)
The I/O Analog Data Point Tag supports the data properties of the Analog Data Point Tag.
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. |
The I/O Analog Data Point Tag builds on the features of these tag types:
To learn about properties common to all analog tags.
To learn about the Core Data Driver.
For the meaning of terms used in Fernhill SCADA.