Model 9120-RPS Function:

The Model 9120-RPS reads a signal from each of the two oxygen probes located in the furnace. Depending on the 9120-RPS configuration, it will select whichever millivolt reading it has been configured to select and retransmit this millivolt output to the atmosphere controller.

 

The probe millivolt deviation band and the alarm delay times are set using the operator interface.  See the section Configuration for more information on how to use the operator interface. When connected per the electrical drawing (section Typical Electrical Drawing), the Model 9120-RPS default configuration is set to retransmit the millivolt signal from the probe with the highest millivolt output. As time passes and if/when the other probe’s millivolt output becomes greater (dependent on the deviation band), the Model 9120-RPS will switch the output from one probe to the other and send the “new” higher (or lower, depending on the configuration) millivolt signal to the atmosphere controller.  The deviation band must be exceeded for the retransmit to occur.

 

The asterisk (*) on the operator interface display indicates which probe’s millivolts are being used by the furnace atmosphere controller. When the Model 9120-RPS switches the output from one probe to the other it indicates a deviation band alarm condition, flashing an A on the operator interface.  The red light in the upper left corner of the operator interface will be lit as well in an alarm condition. The A continues to flash until the probe’s output is back within the deviation band.

 

The operator can manually select the probe that is to be used in the carbon calculation. If this feature is used, the 9120-RPS will use the operator-selected probe, and NOT switch from one probe to the other automatically.  See the section Configuration – Probe (Prb) Select Mode for more information on how to manually select a probe.

 

The deviation alarm is disabled if both probes’ millivolts drop below 950. This should eliminate the nuisance alarm when the furnace is loaded and the temperature drops.