Linear Calibration Ext
Figure 22. Linear Calibration Extension
These properties allow you to “calibrate” the calculated value before is applied to the Out slot, where: [(calculatedValue x Scale) + Offset] = Out value.
Usage is optional, although Offset and Units are commonly configured.
NOTE: In most cases where the parent Nrio proxy point’s facets have been edited from defaults, note you must edit the Units value in the Linear Calibration Ext to match the units in the point facets, otherwise the parent proxy point will have a fault status!
Typically, you see this fault status immediately after you add a new input point, for example a VoltageInputPoint or ResistanceInputPoint, and configure it with a Linear conversion type (including a scale and offset), and then specify the point’s facets. It may not be immediately clear that the problem is in this Linear Calibration Ext, where you must match its Units value to the units in the point’s facets.
- Scale
Default is 1.0. Typically, you leave this at default. One exception is if you copied the LinearCalibrationExt under a CounterInputPoint, in order to get a scaled total (see Note: below).
- Offset
Default is 0.0. Can be either a positive or negative value, as needed. Often, this is useful to compensate for signal error introduced by sensor wiring resistance. If under a CounterInputPoint, leave at 0.
- Units
Set this to the same units as in the parent proxy point’s facets (see Note: above).
- Fault Cause
Provides a reason whenever this extension causes the parent proxy point to be in fault, e.g.:
Units between point and extension are not convertible.You can also copy the linearCalibration extension without error to other Nrio points based on Numeric points. For example, a CounterInputPoint point if a “scaled total” out value is desired. Consider a CounterInputPoint for a flow rate meter that provides a contact closure for every 0.15 gallons, configured as:
- Facets: gallons [units: volume (m^3), gallon (gal)]
- NrioCounterInputProxyExt:
- Conversion: Default
- Output Select: Count
- Rate Calc Type: FixedWindowRateType
- Rate Calc:
Scale: 9.0
Interval: 15s
- LinearCalibrationExt:
- Scale: 0.15
- Offset: 0.0
By copying a LinearCalibrationExt to the CounterInputPoint and specifying the item quantity/pulse as the Scale value (in this case, 0.15), the count output value will read in gallons, rather than number of pulses. Note that the “rate calc” setup provides the “gallons per minute” scaling that will reflect in the Rate slot of the point’s ProxyExt, where Scale was calculated as 60 (sec/min) * 0.15 gal/pulse = 9.