Figure 74 Ratio Control Example - Honeywell HC900 Reference Manual

Function Blocks
PID Function Block
Example 4 - Ratio control
The RATIO control loop requires selection of the
remote SP of the PID for ratio control. The Ratio
and Bias values are available for adjustment
from the Control Setup screen of the Operator
Interface. The Bias may be a local value or come
from an external source such as an O2 analyzer
trim arrangement. You may elect to use % for
the ratioed inputs (typically for boiler
applications) or Eng. Units (EU) (for feed flows to
a reactor, for example).
Air (controlled variable)= Ratio x Fuel (RSP, or wild variable) + BIAS
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Figure 74 Ratio control example

HC900 Hybrid Control Designer Function Block Reference Guide
External Bias
Input
Revision 11
2/07