National Instruments FP-3000 - Manual (Page 40)

Chapter 3 Example Applications
© National Instruments Corporation 3-5 FieldPoint FP-3000 User Manual
This tells the AI block to expect readings in the range of 0.004 to 0.020
Amps (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 when
displaying this value.
2. Determine the pressure in your desired engineering units at 4 mA and
at 20 mA. For example, suppose the sensor reads 10 inH
2
0 (inches of
water) at 4 mA and 250 inH
2
O at 20 mA. Go to the OUT_SCALE
parameter on the Scaling tab and enter the following:
OUT_SCALE
EU_100 250
EU_0 10
Units_Index inH2O
Decimal 3
3. Set the type of scaling. 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 on the Scaling tab to
Indirect .
4. Close the block configuration window.
The block converts the raw 4-20 mA value and reports it in engineering
units through the
PV and OUT parameters of the function block.
Set Up Scheduling
Before the block will operate, you need to schedule the block to execute.
All Fieldbus function blocks (including function blocks on the FP-3000)
execute according to a schedule. You can specify the order of function
blocks in the schedule and the rate at which the schedule is repeated. To
make the NI-FBUS Configurator create a schedule so that your block can
execute, follow these steps:
1. Double-click on Function Block Application in the configuration tree
of the NI-FBUS Configurator. This opens the Function Block
Application Editor window in the middle window of the NI-FBUS
Configurator.
2. Drag the block from the configuration tree to the Function Block
Application Editor window. The NI-FBUS Configurator automatically
generates a schedule for the block that causes it to run every second
(refer to the documentation that came with your configurator for
information about changing the execution period).