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B-11
Analog Input (AI) Function Block
Application Example:
Differential Pressure Transmitter
to Measure Flow
Situation The liquid flow in a line is to be measured using the differential
pressure across an orifice plate in the line, and the flow measurement
will be used in a flow control loop. Based on the orifice specification
sheet, the differential pressure transmitter was calibrated for 0 to 20 in
H
2
0 for a flow of 0 to 800 gal/min, and the transducer was not
configured to take the square root of the differential pressure.
Solution Table B-6 lists the appropriate configuration settings, and Figure B-7
illustrates the correct function block configuration.
Figure B-7. Function Block Diagram for a Differential Pressure Transmitter Used in a Flow Measurement.
TABLE B-6. Analog Input Function Block Configuration for
a Differential Pressure Transmitter.
Parameter Configured Values
L_TYPE Indirect Square Root
XD_SCALE 0 to 20 in.
OUT_SCALE 0 to 800 gal/min.
AI
Function
Block
PID
Function
Block
AO
Function
Block
OUT_D
OUT
Analog
Measurement
BKCAL_IN BKCAL_OUT
IN