Chapter 3 Example Applications
FieldPoint FP-3000 User Manual 3-4
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National Instruments Corporation
Set the Input Range
1. Find the FP_AI_110_RANGE parameter in the block.
2. Set the parameter to 3.5–21 mA, since this range most closely
matches the 4–20mA that you expect from your transmitter.
Scale the Reading
1. Set the XD_SCALE parameter, which tells the block the range of values
to expect from the transducer. Go to the XD_SCALE parameter of the
block and enter the following:
XD_SCALE
EU at 100% 0.020
EU at 0% 0.004
Units Index A
Decimal 3
This tells the AI block to expect readings in the range of 4 to 20 mA
from the pressure sensor. The Decimal field is unused by the FP-3000,
but may be used in some HMIs to determine the number of digits to
display to the right of the decimal point.
2. Determine the pressure in your desired engineering units at 4 mA and
at 20 mA. For example, suppose the sensor reads 10 inH20 (inches of
water) at 4mA and 250 inH2O at 20mA. Go to the OUT_SCALE
parameter of the block and enter the following:
OUT_SCALE
EU at 100% 250
EU at 0% 10
Units Index inH2O
Decimal 3
3. Tell the block to use the scaling parameters. The block is flexible
enough to either ignore scaling (Direct), use linear scaling
(Indirect), or use square root scaling (Indirect square root).
Since you want the block to use linear scaling, set the L_TYPE
parameter of the block to Indirect.
The block converts the raw 4-20 value and reports it in engineering units
through the PV and OUT parameters.