YSZ oxygen sensor

[49078]

Are there any possible alternatives to these zirconia oxygen sensors. We've used them before, and work in many applications but in our nitriding furnace they don't seem to work and I can not figure out why.

Max conditions are 600 deg C, 10-3atm. I read a form on eng tips that mentioned possible causes for the sensors not working, and a common theme was thermal shocks. I do not believe that is a big issue with us.

cheers

 

[ceramax]

Is the nitrogen pressure around 10-3atm? What is the oxygen content range in your furnace that tou want to measure?

 

[JEB66]

could you explain what you mean by "they don't seem to work"?

I have a lot of expierence with these instruments on coal fired furnaces.

 

[49078]

The oxygen is very low, possibly less then 1ppm. I'm not sure the exact content, but it would have entered the system through a opening around a gasket. The system is evacuated, and any presense of oxygen introduced through the cycle will force that cycle to be scrapped.

The N2 pressure is around 10-3atm.

JEB66, in the past ysz sensors are used that showed no signs of oxygen content, then the part would be checked and show that oxygen was present.

This may simply be that the oxygen content is so low that it doesn't register, but I have no previous experience with ysz so I don't know for sure.


cheers

 

[ceramax]

1~5 ppm around 10~3 atm N2, you need a special oxygen sensor set to measure it. There is at least one supplier in US, and you should be able to find it by online search.

 

[49078]

ceramax,

Do you know why ysz sensors don't work in these environments?

 

[ceramax]

My understanding is that YSZ sensor should still be functional in these environments unless electrode is damaged. However, in order to measure ppm Oxygen, it needs a much better electronic hardware to convey signal differences from the YSZ ceramic sensor; a calibrated reference oxygen gas (no air, which is normally used in industrial psz sensors) and a well-controlled temperature around the sensor. A normal oxygen sensor set doesn't have enough accuracy to tell you anything between 0 and 0.1%. If your case, I think you just saw 0% reading. This is like measuring weight between tones v.s. milligrams, or lbs v.s. carats. It requires a much more accurate system to be able to measure ppm oxygen.

 

[EdStainless]

Remember how these sensor work, their resistance goes down at the oxygen goes up. So in order to measure very low levels you need to measure very small differences in very big resistance values. Give the thermal coef of the sensor the temperature must be kept very stable.
I think that you would be better off with a different system for this application.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[saxonsvn]

I think your problem may be the over pressure of your furnace (10 ~ 3 atm). The ZrO2 oxygen probe normally works at a pressure of ca. 1 atm. The accuracy of this sensor is quite high, actually. Furthermore, you can use a little air as additing gas for better responsiveness of your sensor.