Tag scaling allows raw device data to be converted to engineering units for OPC client applications. TOP Server supports direct scaling of device data with with linear or square root formulas. Static Tag creation in the Server is required to use this feature. (Learn more about Static vs Dynamic Tags)
When adding a tag in TOP Server whether manually, through a CSV import, or the configuration API, the following configuration items are available.
Scaling Types
Linear
Is what you would imagine if you graphed the raw values against the scaled values. You would see a straight line. This is what most users require and use.To get very technical, the formula used from the settings above is:
Scaled Value = (((ScaledHigh - ScaledLow)/(RawHigh - RawLow))*(RawValue - RawLow)) + ScaledLow
Square Root
Takes the square root of part of the settings as shown below and adds them to the ScaledLow parameter. This type of scaling is used with some types of instrumentation and your controls engineer would tell you that you need this type.
Scaled Value = (Square root ((RawValue - RawLow)/(RawHigh - RawLow))*(ScaledHigh - ScaledLow)) + ScaledLow
The "Negate Value" setting, which defaults to "No", can be used to negate or make negative, the resulting Scaled Value if your formula requires it.
Other Settings
You can specify the range of the raw data from your device and the engineering range of the scaled value. In some cases the raw data received from a device may exceed the range set for the raw data. If this occurs the engineering value can be forced outside of the range you desire. To prevent this, TOP Server allows you to specify that the scaled value be clamped to the engineering ranges.
In most cases it is always assumed that a scaled value results in a floating point number. TOP Server doesn't make this assumption and allows you to select the scaled engineering value to be any valid OPC data type. This means you can scale a 16 bit integer value to a 32 bit integer value. "Double" is the default data type for all scaled values.
To make scaling complete, TOP Server allows you to specify the engineering units for the scaled tag. A string of up to 32 characters can be entered and attached to the tag. If the OPC Client application in use supports access to OPC tag properties, the data ranges and the units can be used in the OPC client to automatically configure objects like user input or data displays.
If your application requires more than simple scaling and complex math is difficult to configure in your client application, then we suggest using the Advanced Tag Plug-In, Cogent DataHub or OPC Router.
