Emerson Exchange 365

Rosemount oxygen analyzer issue

Hi,

We have 4 oxygen analyzers which we calibrated with 0.4% and 8% gases. The calibration was successful and the parameters for the probe were saved. However, when the analyzer is not reading more than 17% even when put out in the open air or when a sample of instrument air is provided instead of actual flue gas. 

hkhan

• 14 Feb 2019 11:58 AM
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10 Replies

• JesseSumstad

  

  • 14 Feb 2019 3:05 PM

  Hello Hkhan,
  
  Please provide us with a little more information to help answer your question.
  
  1. Can you provide us with what the slope, offset, and cell impedance were after the calibration?
  2. Could you also confirm if you calibrated the unit with the reference air (instrument air) applied?
  3. Could you confirm if you are using reference air while in process?
  
  The O2 cell is sensitive to pressure so if you did not calibrate with reference air applied to the reference side, and then hooked up instrument air for your process readings, the additional pressure on the reference side will cause the measurements to read low.
  
  Thanks,
  Jesse Sumstad

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• Neil Widmer

  

  • 14 Feb 2019 4:21 PM

  In reply to JesseSumstad:

  Also check that the reference air exhaust port is not plugged. This pressurized the reference side causing a higher O2 partial pressure than the sample side.

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• hkhan

  

  • 15 Feb 2019 6:42 AM

  In reply to JesseSumstad:

  1. Paramters:
  O2 cell 2.25mV
  Impedence 46 ohms
  ramp rate 17.3 deg C/s
  2. Yes
  3. Yes

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• hkhan

  

  • 15 Feb 2019 6:43 AM

  In reply to Neil Widmer:

  There is a metallic plug with option to remove via allen key, should be we remove it or does it have a pinhole for vent?

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• Jim McLelland

  

  • 15 Feb 2019 10:01 AM

  In reply to hkhan:

  Hkan ,
  
  Just to be clear . You mention you have four (4) zircona sensor O2 Analysers. If they are all displaying the same low reading when exposed to air , then the comments noted above by Jesse and Neil need to be considered and implemented. Ask for the O2 % versus Mv Chart from The Emerson analytical team . That will give you a guide as to the cell performance.

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• hkhan

  

  • 15 Feb 2019 1:18 PM

  In reply to hkhan:

  Also, the probe slope is 52.36mV/Dec, and calibration constant is -4.57mV

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• Neil Widmer

  

  • 15 Feb 2019 4:36 PM

  In reply to hkhan:

  Sounds like you have the Model 6888A with a vented plug fitting. The hazardous area Model 6888C has a capped port fitting. If you don’t detect vent flow, you could disconnect the reference air inlet, re-calibrate and then test in air to see if the problem goes away. Let us know what you find. Thanks

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• hkhan

  

  • 16 Feb 2019 12:40 PM

  In reply to Neil Widmer:

  Hi Neil, done it. No effect...

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• Mark Olson

  

  • 16 Feb 2019 2:07 PM

  In reply to hkhan:

  What process are the probes in? If in a boiler is it wood fire, coal, or natural gas?
  
  How long has the probes been installed in process are these brand new?
  
  When you calibrate what is the response time when it is going back to atmosphere. If it is more than 45 seconds then you may have partially plugged diffusers.
  
  Calibration:
  what are you using for calibration if it's the calibration kit or if you have stationary bottles with regulators.
  if you are using stationary bottles set the regulator at no more than 20 PSI and the flow meter at 5 SCFH
  Dry Instrument air should be set at 5 PSI and flow meter at 2 SCFH
  
  If you have moisture in the instrument air that will cause problems with calibrations and will have negative calibration constant that you mentioned above.

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• hkhan

  

  • 17 Feb 2019 3:39 AM

  In reply to Mark Olson:

  Yeah, we just had our first fire of the boiler on HSD and in future will burn coal. All analyzers are brand new.

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