Application Examples - Emerson Oxymitter 5000 Instruction Manual

Instruction Manual
IM-106-350, Rev 2.2
July 2008
APPLICATION
EXAMPLES
Basic PID Block for
Steam Heater Control
Figure E-3. PID Function Block
Steam Heater Control
• Local Override is a non-target mode that instructs the block to revert to
Local Override when the tracking or fail-safe control options are
activated.
• Out of Service mode disables the block for maintenance.
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 E-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 E-4 illustrates the correct
function block configuration.
Oxymitter 5000
TCV
101
Steam Heater
Condensate
TC
101
TT
101
E-11