Owner's manual

FOUNDATION
TM
Fieldbus Blocks Manual
A-4
Figure A-5. Function Block Diagram for a Differential Pressure Transmitter Used in a Flow Measurement
ANALOG OUTPUT (AO)
FUNCTION BLOCK
The configuration of an AO function block and its associated output
channels depends on the specific application. A typical configuration for
the Analog Output involves the following parameters:
PV_SCALE Set the range and engineering units to values that
correspond to the operation range. In many cases,
PV_SCALE is set to 0 – 100%.
IO_OPTS Select Increase to Close when the actuator is
designed to fail open.
BKCAL_OUT If you are using the CAS_IN connector wired from
another block, wire the BKCAL_OUT attribute to the
other block’s BKCAL_IN attribute.
Application Example: Using an
AO Block and a Valve to Control
Flow in a Pipe
Situation
A regulating valve equipped with an air-operated actuator is connected
to the analog output channel to control flow in a pipe.
Solution
The Analog Output (AO) function block is used with an AI and a PID
function block. The configuration differs depending on whether the
valve actuator is designed to allow the valve to fail closed or to fail open
upon the loss of power. Table A-5 lists the appropriate settings for each
attribute, and Figure A-6 illustrates the correct function block
configuration.
TABLE A-5. Analog Output Function
Block Configuration Example
AI
Function
Block
PID
Function
Block
AO
Function
Block
OUT_D
OUT
Analog
Measurement
BKCAL_IN BKCAL_OUT
IN
Attribute
Configured Values
Fail Close Fail Open
PV_SCALE 0to100% 0to100%
XD_SCALE 0to100% 0to100%
IO_OPTS Increase
to Close
Not selected Selected