Non-linear sensor support
Providing the kitIo module is installed, the conversion selection Generic Tabular provides a way for a VoltageInputPoint or ResistiveInputPoint to support a non-linear responding signal on a universal input
(using point Facets other than temperature). Note that the ThermistorInputPoint also provides non-linear support for resistance-based
temperature sensors, but point Facets are limited to temperature.
If you select Conversion type of “Generic Tabular” an edit control (note pad icon) appears in the property sheet beside it. Click the icon to see the Tabular Conversion Dialog, as shown in the following image.
Figure 21. Generic Tabular Dialog from edit control
This dialog allows you to edit the current “source-to-results” non-linear curve used by the proxy point, import another curve (.xml file), or export (save) the current curve as an .xml file. In this way you can provide any custom non-linear curve needed. The following image shows a point with a non-linear curve described in the “Non-linear sensor example” topic.
The following notes apply to using this feature:
- A curve requires at least 2 points (rows), each using “Source” to “Results” values.
- Source values use the “Device Facets” of the Nrio proxy point, and must be in the range of the controller input. Therefore, if a VoltageInputPoint, source values must be between 0 to 10 (Volts), or if a ResistanceInputPoint, source values must be between 0 to 100000 (Ohms).
- Result values are typically the measured value, regardless of units, at each source point. This assumes no further scaling using a LinearCalibrationExt—i.e., its Scale property is the default “1”.
- Points are used in ascending order, by the Source column.
- You can add as many points as is needed (there is no hard-coded limit). Click the Add button to add a new row for a point.
- If you skip a point, just add it at the end, and then click Resort. This automatically reorders all points in ascending order, by the Source column.
- Click the delete icon (trash can) beside any point to delete it from the curve. If you click the Delete All button, all points (plus any Description text) is removed (typically, you do this only to enter a new non-linear curve).
- Description text appears in the ProxyExt property sheet, beside the Conversion edit icon.
- When you click Save, the curve configuration is stored as part of the conversion object in the station (there is no association with any external
file, in case you imported a non-linear curve).
NOTE: If you update a non-linear curve (say, add a point) after it was imported in one or more Nrio points, you need to export it (save) and re-import it in other points, in order for them to be updated.