FAQ

• How much oxygen (O2) is in air? 
• How long should I expect my oxygen sensor to last?
• The oxygen sensor I am using with my safety monitor needs replacement every 6 months. I am constantly getting false low oxygen alarms. Is this common?
• What is the difference between trace and percent oxygen?
• When measuring trace oxygen, can I use plastic tubing to deliver the sample to the analyzer?
• Do all trace oxygen analyzers require the user to apply “correction factors” when gases of different molecular weights are used, i.e. helium, hydrogen, methane, etc?
• My sample gas contains hydrocarbons and/or hydrogen along with trace levels of oxygen. Can I use an oxygen analyzer with a zirconium oxide sensor?
• How often should I calibrate my oxygen analyzer?
• What is the difference between sealed electrochemical sensors and those requiring initial charging with electrolyte?
• I found that after calibrating the company’s trace oxygen analyzer on air (209,000 ppm O2), the accuracy of the readings at 75 ppm were way off. Why is this? 
• I am using an oxygen analyzer with a zirconium oxide sensor for portable measurements. The initial sensor lasted less than a year with a replacement cost of over $1,200. Is this common?
• How important is sample conditioning?
• Aren’t all electrochemical sensors the same?
• I have attempted to use an oxygen analyzer with a paramagnetic sensor to measure 350 ppm oxygen. My readings are all over the place, why?
  
  

How much oxygen (O2) is in air? 
20.9% by volume under dry, cool conditions. The reading will vary downward by several tenths of a percent based on prevailing ambient temperature and humidity conditions.
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How long should I expect my oxygen sensor to last?
It varies based on the measuring technology used. Check with the manufacturer to determine projected life of sensor and balance the replacement cost versus its functional life. Also check the warranty.
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The oxygen sensor I am using with my safety monitor needs replacement every 6 months. I am constantly getting false low oxygen alarms. Is this common?
Yes, but it is not necessary. There are some inexpensive electrochemical sensors that have a short operating life. When used for safety monitoring, these sensors cause false low oxygen alarms due to sensor deterioration. For safety applications, it is incumbent upon purchasers to select a product whose sensor life is at least three years or more.
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What is the difference between trace and percent oxygen?
Both expressions denote the volume of oxygen in the sample. Typically, people begin using the terms trace oxygen for values less than 10,000 ppm. 10,000 ppm is the equivalent of 1% oxygen.
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When measuring trace oxygen, can I use plastic tubing to deliver the sample to the analyzer?
Recognizing that ambient air contains 209,000 ppm (20.9%) of oxygen, use of plastic sample tubing exacerbates the chance that an oxygen leak from outside air will taint the readings. A minute air leak can render a measurement useless. Usually, copper or stainless steel tubing is always the materials of choice.
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Do all trace oxygen analyzers require the user to apply “correction factors” when gases of different molecular weights are used, i.e. helium, hydrogen, methane, etc?
Some oxygen sensors are sensitive to gas mixtures. If the sample in question doesn’t change composition, this may not be an issue.  Otherwise, it may be best to consider a sensor that is not affected in this manner. Ask the manufacturer before purchase.
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My sample gas contains hydrocarbons and/or hydrogen along with trace levels of oxygen. Can I use an oxygen analyzer with a zirconium oxide sensor?
For applications where reducing gases such as hydrocarbons, carbon monoxide, hydrogen, etc. are present, zirconium oxide sensors should never be used. The sensors operate at temperatures of approximately 600 degrees. With the use of platinum electrodes, the presence of the aforementioned gases will interfere with the oxygen measurement resulting in lower than actual readings. Oxygen readings may be affected as much as 50% or greater, depending on the concentration of reducing gases.
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How often should I calibrate my oxygen analyzer?
The frequency of calibration is usually governed by the quality of the oxygen sensor and mating electronics. Some oxygen monitors require weekly calibration checks while for others, the intervals between calibration checks may be months. Notwithstanding in-house calibration protocols, an oxygen analyzer, with a good quality sensor, will require infrequent calibration checks.
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What is the difference between sealed electrochemical sensors and those requiring initial charging with electrolyte?
There are a number differences, the most obvious is that analyzers that feature a sealed oxygen sensor do not require the addition of potassium hydroxide (caustic) prior to start-up. Open reservoir sensors also require the user to replenish the electrolyte on a frequent basis.
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I found that after calibrating the company’s trace oxygen analyzer on air (209,000 ppm O2), the accuracy of the readings at 75 ppm were way off. Why is this? 
Though checking a trace oxygen analyzer’s calibration on air may seem  expedient, good calibration techniques suggest using a calibration gas with an oxygen concentration within the range of the analyzer. Calibrating on 209,000 ppm of oxygen and then expecting high precision readings at concentrations < 1,000 ppm is precarious.
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I am using an oxygen analyzer with a zirconium oxide sensor for portable measurements. The initial sensor lasted less than a year with a replacement cost of over $1,200. Is this common?
Some manufacturers of zirconium oxide oxygen analyzers caution against using the analyzer for portable use. The constant heating and cooling of the zirconium sensor may result in “thermal shock” and cause premature failure of the sensor.
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How important is sample conditioning?
Proper sample conditioning may, in all likelihood, be the reason behind a successful long-term monitoring application. Prior to selecting an oxygen analyzer, be sure to discuss the application in detail with the manufacturer and seek their expertise in the area of sample conditioning to include; filtering, temperature control, aspiration, pressure regulation, scrubbing of undesirable sample components, etc.
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Aren’t all electrochemical sensors the same?
Though the electrochemistry is similar, selection of materials, manufacturing processes, electrode surface activity, etc. differentiates many sensor manufacturers. Like most things in this world, all electrochemical sensors are not alike.
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I have attempted to use an oxygen analyzer with a paramagnetic sensor to measure 350 ppm oxygen. My readings are all over the place, why?
This dilemma points to the fact that each oxygen measuring technique has its strong points and potential deficiencies. It is incumbent upon manufacturers to fully understand the customer’s application before making a recommendation. In general, paramagnetic sensors do not have the measurement sensitivity to provide accurate and repeatable readings in the low parts per million range. In this case, the paramagnetic sensor was misapplied.
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