Honeywell HC900 - Figure 74 Ratio Control Example

Function Blocks
PID Function Block
290 HC900 Hybrid Control Designer Function Block Reference Guide Revision 11
2/07
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).
External Bias
Input
Air (controlled variable)= Ratio x Fuel (RSP, or wild variable) + BIAS
Figure 74 Ratio control example