Scale and offset calculation (linear)

Unless you want a VoltageInputPoint or VoltageOutputWritable to operate with facets (units) of volts, you must set the point’s facets to the desired units, and change the Conversion property in its ProxyExt. Typically, you select a Conversion of Linear, except in the case of VoltageInputPoint used for a 4-20mA sensor, which requires a conversion of 500 Ohm Shunt, with Linear as the secondary conversion.

Linear conversion is also appropriate for a linearly-responding ResistiveInputPoint using facets other than ohms—although this may be less common than a non-linear application.

Linear requires you to enter your calculated scale and offset values in the Linear fields. Also, if an input point, you must set the “Units” in its Linear Calibration Ext to match an input point’s facets—otherwise a fault status occurs.

Use the following formulas to calculate the Linear scale and offset values:

where: x1 and x2 are the Nrio values (e.g voltage), and y1 and y2 are the corresponding desired units.

Scale
Scale = (y2 - y1) / (x2 - x1)
Offset
Offset = y1 - (Scale * x1)

See example 1 and example 2.

Scale and offset calculation (linear)

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