AFRC Controlling the Engine

If AutoControl is used on the AFRC Advanced, the final alarm in the Alarms Setup screen (Pg. 206) is the “AutoControl Range” alarm. This alarm can be used to fall back from “AutoControl” to “Setpoint” mode in the event the Post Catalyst O2 sensor milliVolt reading is pushed outside the set range, which can indicate the sensor is failing.

On a trigger of the alarm condition, the AFRC will go into “Setpoint” mode with a target setpoint valve defined by the alarm. The default is “777”. To change the fallback setpoint value, select the “Setpoint: 777” button within the alarm row.

This event will trigger an alarm, AFR062 (min trigger) or AFR063 (max trigger), on the Alarms screen (Pg. 40). This alarm must be reset in order to switch back from “Setpoint” mode to “AutoControl” mode. A security access level of Setup or Engineering is required to reset the alarm.

Controlling The Engine

Detecting the Run Signal

With the engine running, the AFRC will detect the engine operation through the sensor trigger defined within the Run Signal Trigger screen (Pg. 10). If a valid run signal is recognized, the black text in the header next to the “Home” button will display “Eng: Run”.

Sensor Warm Up

Upon detecting the system run signal, the bank status within the control box will display “Heater Warmup” indicating the sensors have been started. After the sensor heaters are warmed, the AFRC will be ready to control. When the AFRC is ready, and in “Manual” control mode, the bank status will display “Ready” and will wait until the control mode is transitioned from “Manual” to “Auto”. A security level of Setup or Engineering is required to toggle the control mode.

If the AFRC is already in “Auto” mode, it will start the process for initializing control.

Load Delay

Once the sensor is warm and in “Auto” mode, the AFRC will go into a load delay. By default, the load delay waits 30 seconds before the controller starts to move the valve.

If an AFRC Advanced is used and “Auto Control” is enabled, the controller not transition to delay mode until the pre-catalyst or post-catalyst thermocouple read a light off temperature of 550 degrees F.

Starting Control

When starting control, the bank status will update to “Attempting To Control”. The valve will automatically adjust to try and match the actual O2 reading with the desired target setpoint. As the valve finds the position that’s meets the target and is stable, the status will update to “Controlling”.

Optimizing The Target Setpoint

The oxygen target setpoint “Target” should be set to optimize catalyst performance. This should be conducted while the engine is at a normal operating temperature and under normal loading. An exhaust gas analyzer should be used to reach optimum performance.

If an AFRC Advanced is used and “Auto Control” is enabled, no target setpoint adjustment is necessary.

External Dynamic and “600” Series Manual Valve Adjustment

If an external dynamic or 600 series valve is in use and the desired oxygen sensor target setpoint cannot be reached, then the valve will need manual adjustments. These valves contain an external “load” screw, which must be rotated to make adjustments (for more information, refer to “APPENDIX D. EXTERNAL DYNAMIC AND 600 SERIES VALVES”).

STOPPING THE ENGINE

The engine may be stopped at any time. The AFRC will detect the engine has stopped based on the trigger selected on the Run Signal Trigger screen (Pg. 10). When using thermocouples as the run indicator (“AFRC Pre-Cat TC” or “EMD Pre-Cat TC”), the controller will detect the engine has stopped after the pre-catalyst thermocouple drops below the trigger point (450°F by default). When using an oil pressure switch (“AFRC Oil Pressure” or “EMD Oil Pressure”), AFRC RPM, or Ignition State, the controller will immediately detect the engine has been shut down.

After the controller detects a shutdown, the digital power valve will fully open and then move to the startup position. This digital power valve cycle is repeated once after each engine shutdown to maintain calibration of the digital power valve position.