Справочник Пользователя для National Instruments FP-3000
Chapter 3
Example Applications
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 4–20 mA 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
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.
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 4 mA and 250 inH2O at 20 mA. Go to the
at 20 mA. For example, suppose the sensor reads 10 inH20 (inches of
water) at 4 mA and 250 inH2O at 20 mA. 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 (
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
through the
PV
and
OUT
parameters.