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Revised 2/1/2019
JENE-EG534-V2
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Scale and offset calculation… Example 2
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 -10in.wc. to
+10in.wc. Configure this point’s facets to have units: “pressure,” “in/wc”.
Set the ProxyExt’s Conversion property to use “500 Ohm Shunt” (if available), 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
Figure 3-12 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.
Non-linear sensor support
The conversion selection Generic Tabular provides a way for a VoltageInputPoint or ResistiveInputPoint to support a
nonlinear 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
Figure 3-13.
Figure 3-13 Tabular Conversion Dialog from edit control
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