You have a linear 4-to-20mA differential pressure sensor to read with a VoltageInputPoint (using an external 500 ohm resistor
wired across the input), reading effectively 2V to 10V. The range of this sensor is from -10 in.wc. to +10 in.wc. Configure
this point’s facets to have units: “pressure,” “in/wc”.
Set the ProxyExt’s Conversion property to use “500 Ohm Conversion”, then “Linear” as secondary, and in the Linear fields enter
these calculated scale and offset values:
- Scale
Scale = (y2 - y1) / (x2 - x1)
Scale = (+10in.wc - -10in.wc) / (10V - 2V) = 20/8 = 2.5
- Offset
Offset = y1 - (Scale * x1)
Offset = -10in.wc - (2.5 * 2V) = -10 - 5 = -15
The following image shows this point’s configuration in a
Workbench dialog. Note that the Linear Calibration Ext for this point will require its “Units” property to be configured to match the
facets for this point—otherwise, the point will have a fault status. See the “Linear Calibration Ext” section for related
details.