Honeywell SmartLine ST 800 - Page 41

31 ST 800 Pressure Transmitter User’s Manual Revision 15
the displayed PV to the
desired value when PV
Scaling is set to either
Linear or Square Root. See
Notes 1 and 2
Below.
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NOTES:
Screen configuration only affects the value shown on the Display. It does not affect the Loop Output.
1. Linear scaling of the displayed PV value
When “Linear” is selected for PV Scaling, the display will scale the selected PV input
according to the following formula:
((PV value – input low limit) / input span) x (Scaling High – Scaling Low) + Scaling Low
If the PV Selection is Pressure, the input low and high limits are the LRV and URV
respectively. If the PV Selection is Percent Output, the input low and high limits are 0 and
100%. If the PV Selection is Square Root, the input low and high limits are 0 and 100
%Flow.
Note that this scaling only affects the value shown on the Display; it does not affect the Loop
Output.
2. Square Root scaling of the displayed PV value
When “Square Root” is selected for PV Scaling, the display computes %Flow from the
Differential Pressure. This calculation is independent of the Transfer Function setting in the
transmitter. This allows the user to output Differential Pressure via the 4-20 mA loop output
while displaying the equivalent flow value on the Display. In addition, the display value can
be scaled to show the flow in flow units (gal/min, gal/h, etc.) by entering the correct scaling
limits via the Scaling Low and Scaling High parameters.
For example:
PV Selection: Differential Pressure
PV Scaling: Square Root
Scaling Low: 0.0
Scaling High: 2500.0
Display Units: gal/h
LRV: 0.0
URV: set as required by the process