ProFire PF3100 Product Manual page 168

17.8.2 FUEL-AIR RATIO CONTROL (FARC)
The following section provides an overview of the PF3100 FARC capabilities. Refer to the
for additional details and configuration instructions. A FARC system consists of a forced draft appliance with
actuators controlling air flow and fuel flow and up to three additional actuators controlling other process inputs.
The PF3100 allows specific actuator positions to be configured in 5% firing rate increments to control the fuel-air
ratio of the combustion inputs across the entire operating range of the appliance.
17.8.2.1 BASIC FARC
A basic FARC application controls fuel and air channels only. Feedback signals from these actuators are
monitored by the system to ensure that the fuel-air mixture is within the configured parameters.
17.8.2.2 MULTICHANNEL FARC
Up to three additional channels may be added for advanced FARC applications consisting of additional process
inputs (e.g., flue gas recirculation, auxiliary fuel supply, etc.). Configuration options on the additional channels
allow for flexibility in terms of position feedback and cross limiting requirements.
17.8.2.3 O TRIM
2
The addition of a stack oxygen sensor allows for a FARC channel to be trimmed to achieve optimal efficiency while
maintaining the configured fuel-air ratio within the configured parameters.
17.8.3 DEADBANDS
Deadbands are applied under certain conditions to avoid fluctuations between states when a process variable is
close to its configured setpoint or trip point.
17.8.3.1 TEMPERATURE DEADBANDS
Temperature deadbands are applied to prevent valve chattering when a temperature reading is near a configured
setpoint. Generally, the deadband is ignored on the transition from one state to another in one direction but is
applied on the transition in the reverse direction (e.g., For a system configured for High Fire Valve control with
Low Fire enabled (see image below), the deadband is ignored on the transition from Low Fire to Pilot (transition 4)
but is applied on the subsequent transition back to Low Fire (transition 5). Similarly, the deadband in ignored at
transition 3, but applied at transition 6).
Process Temperature
Low Fire Setpoint
Process Setpoint
17.8.3.2 4-20mA INPUT DEADBANDS
4-20mA input deadbands are applied to both the High and Low Trip setpoints when clearing trip conditions only.
The system registers a high trip event as soon as the input reading exceeds the configured High Trip setpoint and
clears the event only after the input reading has dropped below the High Trip setpoint minus the deadband.
Similarly, a low trip event is registered when the input reading dops below the configured Low Trip setpoint and
clears the event only after the input reading has risen above the Low Trip setpoint plus the deadband.
Copyright © 2022, Profire Energy. All rights reserved.
855.PRO.FIRE | PROFIREENERGY.COM
4
Deadband
3
Deadband
2
1
Controller State transition
0 Waiting to Ignition to Pilot
5
1 Pilot to Low Fire
2 Low Fire to High Fire
6
3 High Fire to Low Fire
4 Low Fire to Pilot
5 Pilot to Low Fire
6 Low Fire to High Fire
PF3100 Product Manual
DOC-001149 v8.0
PF3100 FARC User Guide
168