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Technical Support FAQ

3290Z - Percent Oxygen Analyzer (ZrO2 sensing)

What gas should be used for calibration?
What is the pressure dependency of the sensor?
We have a brand new model 3290 that runs for a few hours and then looses its calibration, driving the reading high, shutting down our Nitrogen membrane plant. It read ~6 - 7%, and then the reading went to over 40% Oxygen. It is impossible to be over 21%. We can calibrate it over and over, but it keeps doing the same thing. Why?
I have 4 of the subject analyzers and all have an alarm indicating the sensor is failed. This is not true as the instrument will calibrate and function perfectly. Can you give some other reasons that this could happen. We own and operate one of the largest gas turbine power plants in Asia and I can't accept the vendor's statement that the unit is supposed to blink if within range.
How do atmospheric conditions impact O2 sensor readings?
What is the maximum resistive load on the 4-20mA analog output?
What gases can harm the zirconium oxide sensor?


What gas should be used for calibration?

Please refer to the following document:

Generally this unit can be calibrated on instrument-grade air or ambient air, which contains 20.9% (by volume) oxygen. This is providing the sensor is operated seeing atmospheric pressure (e.g. venting to an atmospheric vent).

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What is the pressure dependency of the sensor?

The pressure dependence of the sensor signal is in the range of 150 mbar ... 800 mbar 2.0 % of measuring signal / 100 mbar in the range of 800 mbar ... 5.0 bar 0.5 % of measuring signal / 1 bar

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We have a brand new model 3290 that runs for a few hours and then looses its calibration, driving the reading high, shutting down our Nitrogen membrane plant. It read ~6 - 7%, and then the reading went to over 40% Oxygen. It is impossible to be over 21%. We can calibrate it over and over, but it keeps doing the same thing. Why?

There are several possibilities.

How are you calibrating the sensor? Are you calibrating it in open air or against a standard cylinder of gas? If somehow the cylinder or calibration method is flawed, theses are the results you might get

the other possibility is a damaged sensor (you mentioned earlier it might have frozen?). That might have damaged it somehow, although I would not say it is likely.

It could however, be a generically just bad sensor.

the other possibility is somehow the electronics are damaged or defective.

One other thing to look at is the interconnect wiring. There are four wires from the sensor (two for the sensor itself, and two for the thermistor). If the thermistor wiring is intermittent, it can do exactly what you say happens. This should be checked carefully.

Another possibility is RFI. If there is a strong RFI surge, it can couple into the wiring and cause a spike lasting a second or two.

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I have 4 of the subject analyzers and all have an alarm indicating the sensor is failed. This is not true as the instrument will calibrate and function perfectly. Can you give some other reasons that this could happen. We own and operate one of the largest gas turbine power plants in Asia and I can't accept the vendor's statement that the unit is supposed to blink if within range.

The unit has a low low O2 alarm fixed in the sw that detects the condition when the sensor anode is completely dead. As this is a percent O2 unit the expectation of the designers was that in application there would be enough O2 in the stream so that the low low o2 condition would not occur.

I suspect you are sampling unusually pure gas that is causing this alarm to flash. You are correct, in this case the sensor is indeed okay.

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How do atmospheric conditions impact O2 sensor readings?

Please refer to the following document:

impact_of_atmospheric_conditions_on_O2_readings.pdf

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What is the maximum resistive load on the 4-20mA analog output?

Maximum resistive load is 500 ohms.


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What gases can harm the zirconium oxide sensor?

Streams containing H2S or Sox, organic vapors or halogens (e.g. F, Cl, Br) should be avoided, as well as water or condensed humidity.


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