This section describes how to use the fields in the Scaling section of the Analog Point tab for analog points on the Advanced OPC driver. The Scaling section allows you to specify the range of the raw input signals, so that they can be suitably converted into floating-point engineering values for use in the Geo SCADA Expert database.
The raw to engineering scaling only applies to integer data types. The Data Type field defines the type of values the OPC server returns for the point (except when Canonical Type is chosen), and then the OPC server determines the data type. Single/double precision floating point types are considered to be in engineering units by default, (see List of OPC Data Types).
If the point can also be written to, the settings in the Scaling section perform a similar conversion on any output signals. Geo SCADA Expert uses the conversion calculation to produce a raw data value (integer data types only) that is sent to plant.
There are two levels of scaling that can be applied to an Advanced OPC analog point. The first level is scaling a raw value into an engineering value using linear interpolation. The second level of scaling is where the Multiplier and the Offset values are applied. This second level of scaling is always applied.
Use the following fields to configure the scaling settings:
- Enabled—Select this check box to enable raw to engineering scaling of the analog data. This check box only applies to analog points with an integer data type.
Geo SCADA Expert uses the Raw Full Scale, Full Scale, Raw Zero Scale and Zero Scale values to produce a scaled value.
Clear the check box if Geo SCADA Expert should not apply any scaling to the integer values it receives from the OPC DA server. Geo SCADA Expert will still apply the Multiplier and Offset to the value.
- Raw Full Scale— Enter the uppermost limit for a raw integer value that Geo SCADA Expert receives from the OPC DA server. The maximum range depends on the data type. Geo SCADA Expert scales this value to the Full Scale value specified within the Alarm Limits section of the tab (see Alarm Limits).
- Raw Zero Scale— Enter the lowest limit for a raw integer value that Geo SCADA Expert receives from the OPC DA server. The minimum range depends on the data type. Geo SCADA Expert will scale this value to the Zero Scale value specified within the Alarm Limits section of the tab (see Alarm Limits).
Example:
Geo SCADA Expert receives integer values from the OPC DA server in the range 0 to 32767. The values need converting so that they are in the range 0 to 100.
In this situation, you would set the Raw Full Scale to 32767 and the Raw Zero Scale to 0. In the Alarm Limits section you would set the Full Scale to 100 and the Zero Scale to 0. Geo SCADA Expert would then scale the values to the range 0 to 100.
- Multiplier—Use this to define the multiplier that is applied after any raw to engineering scaling. Leave the field set at the default of 1 if you do not want Geo SCADA Expert to apply a different multiplier.
- Offset—Use this to define an offset that is applied to the value after any raw to engineering scaling.
If you specify a Multiplier, then the offset is applied after the multiplier. Geo SCADA Expert then stores the result in the Geo SCADA Expert database. Leave the field set at the default of 0 if you do not want to apply an offset.
Example:
For example, to convert Celsius values to Fahrenheit:
The Multiplier would be 1.8
The Offset would be 32
Geo SCADA Expert applies this scaling to produce a value in Fahrenheit.
To scale a value in Celsius of 50, Geo SCADA Expert multiplies this value by 1.8, then adds 32 to the value (that is, (50 x 1.8) + 32 = 122). It then stores the result (that is, 122) in the Geo SCADA Expert database.