Closing an analogue loop for trim control

[Oxidation]

Anybody have a smart way of closing an analogue loop & using a feedback signal as a 'trim output'?

This is an SLC5/04 with PV1000. Its controlling a burner with no oxygen signal feedback, I want to add the oxygen signal as a trim to the analogue output for the heat demand signal. Use the oxygen signal as a 'demand' or 'set point' may also be an alternative idea.
Currently the unit uses a fixed table in memory for driving output to gas & air valves so for example at 10% heat demand the air valve is 17% & the gasw is 5%.

 

[HEC]

Oxidation,

Demand should drive the fuel valve. Air flow control is driven from a variable ratio from either the demand or fuel flow. The O2 measurement is then used to set the ratio value for the air flow output.



Mark Hutton