Engineering unit support distinguishes between absolute temperatures (for example, Celsius and Fahrenheit) and differential temperatures (for example, degrees Celsius and degrees Fahrenheit). The Lon driver modules support special SNVT types for differential temperatures (for example, SNVT_temp_diff_p). Some controllers were designed before these units were introduced. As a consequence, these devices may have certain nvs defined as absolute temperatures, when in fact they are intended to be differential temperatures.

For unit conversion purposes, if you know which variables and properties (nvi, nvo, nci) in a Lonworks device should be treated as a differential temperature, you can edit its corresponding device Lon Xml file in a text editor. Using this edited Lon Xml file in Workbench to define Lonworks devices ensures that unit conversions are performed correctly.

Do this for any affected nv or nci by adding +diff to the snvtType attribute, as shown:

As an alternative to editing device Lon Xml files, you can change the facets/units in the associated Lon proxy points under a device.