If the calibration gas flow is high and it is left to flow on a sensor at a high temperature for more than about 15 seconds,
the ceramic parts of the sensor and sensor sheath can be cooled to the point where, when the flow is removed, they can
break due to thermal shock. If the flow is kept on for a long time it should be reduced slowly to allow the ceramic
surfaces to heat at a rate of not more than 100°C (210°F) per minute.
The sensor accuracy should be within 1% of the EMF according to the tables, with the same offset which was measured
with air on both sides of the sensor. If the sensor EMF is not within this tolerance, then it will require the electrodes to
be refurbished.
Occasionally, a sensor can develop offset with a polluted electrode caused by contaminants in the sample gas stream.
In this case, the old electrode material must be completely cleaned off before re-applying the fresh electrode material.
Again, return the sensor or sensor to Teledyne Analytical Instrumentsor an accredited service organisation.
6.9 OXYGEN SENSOR THERMOCOUPLE
The oxygen sensor is fitted with a ‘K’ type thermocouple to measure the temperature of the oxygen sensor. This
temperature is used in the calculation of oxygen and the control of the heater. The Analyzer has an alarm function
which will advise the operator of an open circuit thermocouple, however bench testing can be performed by simply
measuring the thermocouple continuity.
6.10 HEATER FAILURE
A heater failure will cause a ‘Sensor Temperature’ or ‘Heater Fail’ alarm. Heaters can be tested with a continuity test.
The heater impedance should be approximately 100Ω. Should the heater be open or short circuited, replace the sensor
assembly.
6.11 CO2 OPTICAL SERVICE
Ensure that a particle filter is always fitted on the hypodermic needle to protect the CO
2
analysis chamber.
Do not under any circumstances tamper with or open the CO
2
analysis chamber. Doing so will void the
manufacturers warranty. There are no user serviceable parts inside.
Any tampering will drastically reduce it’s performance and lifetime. (Factory calibration values will be disturbed)
If the carbon dioxide sensor fails, it should be sent back to the manufacturer for repair, and factory re-calibration.
Page 44 Teledyne Analytical Instruments 9070 Oxygen Analyzer
