Emerson Oxymitter 5000 Instruction Manual page 153

Application Example: Basic PID
Block for Steam Heater Control
FIGURE C-3. PID Function Block
Steam Heater Control Example.
FIGURE C-4. PID Function
Block Diagram for Steam Heater
Control Example.
Outlet
Temperature
Input
AI
Function
Block
TT101
Model 4081FG Oxygen Analyzer with F
Abrupt changes in the quality of the input signal can result in
unexpected loop behavior. To prevent the output from changing
abruptly and upsetting the process, select the SP-PV Track in Man I/O
option. This option automatically sets the loop to Manual if a Bad input
status is detected. While in manual mode, the operator can manage
control manually until a Good input status is reestablished.
Situation
A PID block is used with an AI block and an AO block to control the flow
steam used to heat a process fluid in a heat exchanger. Figure C-3
illustrates the process instrumentation diagram.
Steam Supply
TT
100
Solution
The PID loop uses TT101 as an input and provides a signal to the
analog output TCV101. The BKCAL_OUT of the AO block and the
BKCAL_IN of the PID block communicate the status and quality of
information being passed between the blocks. The status indication
shows that communications is functioning and the I/O is working
properly. Figure C-4 illustrates the correct function block configuration.
BKCAL_IN
PID
Function
Block
OUT IN
TC101
fieldbus Communications
OUNDATION
TCV
101
Steam Heater
Condensate
AO
Function
OUT CAS_IN
Block
TCV101
TC
C
101
TT
101
BKCAL_OUT
OUT
C-11