Installing an Elbow for Accurate Measurement

It will make stuff-all difference. Make sure the elbow is a gold-plated-platinum one when the quote goes in...

Do as the customer wishes.

It doesn't work now, does it?

Maybe you will learn something in the process.

You say that you get a correct response with a calibrated source but the customer believes that their uncalibrated gas under a different condition (no heater) reports an inaccurate response. I'm not familiar with the Physics of your instrumentation but using any sensor out of the specified conditions of operation should change the calibration. That is why the conditions are specified. So this comes down to a question of business and contracting. What does your contract say? If the contract specifies this angle, no heater and calibration then you designed the wrong system and should comply. If the contract specifies your design then this is an "out of scope" change to the design. Now your customer maybe lucky that the plenum geometry of the gas flow across the sensor with this elbow will still be a valid gas sample and not a pocket of gas that will exchange randomly. As far as the heater goes you may have to just acquire a heater less oxygen sensor.

It's Zirconium sensor and operates on 615 c. Ya it is possible there might be fault in designing but we are not the one who designed the palnt. No heater means heaters are not running so the percentage of oxygen should be of amibient air which is 20.9. I have installed 100's of this sensor but never faced any problem like this before.

Lets take two steps back here...

What kind of O2 Analyzer are you working with?

Is it In Situ or Extractive?

What components are in the stack and what is the temperature?

It is zirconium sensor operating at 615 C and we are using methane as fuel so the flue gas would be NOX, COX and unburned Oxygen. The model is Ametek WDG and it's type is INSITU.

615 degrees is a pretty hot stack for an insitu probe have you verified thats not over the ameteks operating range? Dont have a huge amount of experience with those units specifically but it does seem a bit hot for that type of analyzer.

How far out are these readings and what are you expecting for a O2 reading in the stack? I dont understand the part where you said with the heaters off you're reading 17-19%? Which heaters?

Is it possible that the velocity of the stack gas is high enough or cold enough to cool the sensor below it's operating temperature range?

Is it possible that the air supplying the stack is actually a bit low in O2?

I suspect that (1) the 45° angle is to prevent any condensation (under those conditions) from staying on the zirconium oxide, and that (2) the filter and the 90° fitting are on the inside of the stack? If these are, it should make the installation interesting, but beyond that I don't really expect this to have much effect on the probe's accuracy. I would be more concerned that gases entering the antechamber nearest the sensor would not be kept moving, thereby causing the sensor to have a response time limited by the rate of diffusion of oxygen in and out of the antechamber.

My concerns exactly but much more clearly stated.

Thank you Fred.

Some ideas that may need considering.

Is the relationship of your measuring linear?

Are you setting zero with your 2% gas or setting the zero point to 2%

The calibration range should always span the measuring range and not be outside it - particularly top span 10% and measuring 20%

Try using normal air which will give 20.9% or thereabouts depending on temperature and pressure.

When you adjust zero 2% does the 'electronics' set that point at a null? What can sometimes happen is that setting zero and then setting high causes the calibration point at zero to change and therefor you will need to reset high which will then cause a small change at low which will cause high to be changed which in turn will change low - this will need to be done until the changes are so small they will have little effect.

When I was dealing Will oxygen electrodes (platinum), the zero calibration point was set at 0mv and by changing the gain to the high set point had no effect on the 0 mv