Troubleshooting

When trouble arises with an oxygen control system, it is important to establish where the problem is located: the sensor, signal transmission lines, the control instrument, or the combustion chamber itself. Several simple tests can help to isolate the problem quickly. It is most important to first understand the nature of the fault. Aside from erratic behavior like cycling, or failure to stabilize at the setpoint, the most common symptom is non-conformity of the work pieces to quality assurance specifications.

 

To evaluate most faults, the recommended tools are:

 

  1. A 3 1/2-digit millivoltmeter with at least 10 MΩ input impedance and 0 to 1999 mV range;

 

  1. A temperature calibrator; and

 

  1. A simulator to output 0 to 200 millivolts at less than 50 MΩ output impedance.

 

Sensor troubleshooting:    In order to establish the source of problems in your installation, first avoid removing the SuperOXTMSensor from the furnace. All of the following meaningful questions must be answered while your sensor is at temperature and is exposed to a normal atmosphere under manual control:

 

  1. Are the connections from the T/C extension wire and sensor cable clean and firmly attached at the correct sensor and control instrument terminals? Note that the shield wire in the sensor cable should be connected to ground at the control instrument end only!

  2. Is the sensor impedance less than 50 KW at temperatures above 1550°F?  Conduct the test shown in Figure 3 using a shunt resistor of about 100 KW. Measure the voltage EC before shunting, then EM with the shunt in place. Calculate RP. If it exceeds 50 KW, proceed to step 6 below.

  3. How quickly does the sensor react to a change in O2 concentration? Read the sensor millivolts with the controller or the digital meter. Short the sensor for 5 seconds, remove the short and measure the time required to return to within 1% of the original reading. If it exceeds 60 seconds, proceed to step 6, below.

  4. Is there a leak in the zirconia substrate? To test this property, turn off the reference air for one minute. Measure the sensor mV as indicated by the controller or a digital voltmeter. Turn the air back on and measure the mV again. If there is a difference greater than 5 mV, replace the sensor.

  5. Should it be necessary to remove your SuperOXTM Sensor from a hot furnace, do so carefully.  UNDER NO CIRCUMSTANCES should it be removed faster than 4" (101.6 mm) per 5 minutes.

  6. If your atmosphere control problem cannot be resolved, our technical support staff is available Monday through Friday, 7:00 a.m. to 6:00 p.m. Eastern Standard Time. You may call us at (513) 772-0060.