Frequently Asked Questions

A: As an organic solvent, there is no issue with acetone nitrile in the background.​

A: Although Teledyne does not warrant the extended storage of fuel cell oxygen sensors at temperatures below freezing (zero degrees Celsius), in general it will cause no permanent damage to the sensor to freeze it.

At temperatures below zero the sensor will stop working, however, as the aqueous electrolyte will freeze and cease to function. If the sensor is gradually warmed to temperatures above freezing, normal operation typically resumes.​

A: No. The shelf life is primarily a function of oxygen exposure. For this reason most fuel cells are packaged in inert atmospheres which maximizes shelf life.​

A: The Micro-fuel Cell is a partial pressure device. Its reading is proportional to the partial pressure of the oxygen in the sample. So at 100 percent oxygen, you get (100/20.9) times the output voltage in air -- assuming the concentration of oxygen in air is this concentration. In highly humid environments, this is not strictly true.

To calculate the effect on the reading, first determine the pressure on the sensor from the sample at the time of calibration or the last reading prior to the pressure change. Then the percentage change in the (absolute) sample pressure will be reflected in a similar if not identical percentage change in the oxygen reading.

Example: If the nominal pressure at which the sensor is used and calibrated is 75 mbar gauge pressure, than the absolute pressure the sensor sees is 75 + 1013.25 = 1088.25 mbarA (As Absolute Pr. =Gauge Pr. + Atm.Pr.) 

If the pressure changes to 200 mbar, 200 mbar gauge pressure = 200 + 1013.25 =1213.25 mbarA 

So, the change in output = ((1213.25-1088.25)/1088.25)*100 = 11.486% (which is positive).​

A: No. vinyl acetate will severely degrade the performance of the sensors almost immediately. Do not attempt to use Teledyne's sensors in the presence of vinyl acetate.​

A: The B-2C sensor is specific to oxygen. However there are a few gases that may be seen by the sensor as oxygen.

Those would be strong oxidizing agents; agents that are as strong or stronger than oxygen such as the halogens Chlorine, Ozone, strong NO, Peroxide. etc.

Some interference is positive, like CL = 1:2, while others like CO are negative. For specific concerns and questions, don't hesitate to contact Teledyne at Ask_TAI@Teledyne.com​.​

A: The Micro-fuel Cell is a partial pressure device. Its output is proportional to the partial pressure of oxygen in the atmosphere to which it is exposed. In the case of altitude effects on sensors exposed to atmospheric oxygen, keep in mind that the volume percentage of oxygen is constant in the atmosphere as one goes higher in altitude. However, the total atmospheric pressure decreases by 2.5 mm/Hg per every 100 feet of altitude rise.

The total pressure of the atmosphere at sea level is 760mm Mercury. At 100 feet of elevation above sea level, the output of the sensor would decrease by a factor of (760 - 2.5) / 760. For example, the new output of sensor at 100 feet elevation = (sensor output at sea level) * (760-2.5) / 760.​

A: The sensor sees atmospheric pressure since the sensor needs to be vented to atmosphere. The sensor's output is directly proportional to vent pressure. Therefore, if vent pressure rises from 1 atmosphere (14.7 psi) to 14.9 psi, than the output will increase by a factor of

= (14.9) / (14.7)

= 1.014​

A: The B-2C trace oxygen sensor is based on an electrochemical system with a silver-plated electrode as the cathode, lead as the anode (pressed granular lead), and an aqueous solution of 10% potassium hydroxide as electrolyte.

The following drawing shows a cross-sectional view of the sensor. In the presence of oxygen, the sensor creates a current that flows from cathode to the anode as a result of the following electro-chemical reactions:

Cathode: 02 + 2H20 + 4e- -----> 4OH- 

Anode: 2Pb --> 2Pb2+ +4e-

A standard B-2C has 6 grams of lead in solid form when the cell is made. After the cell has been used, the solid lead is slightly reduced and the ionic lead inside the electrolyte increased. The ionic form of lead in 10% KOH is at the ppm level. The life of this sensor will depend on the history of the sensor, such as how long it has being exposure to high oxygen levels and / or how long it has been used.

Since the B-2C is design for sensing ppm levels of oxygen, the lead consumption is very low. Most of the lead is not consumed and only a small amount is used by the cell during the lifetime of the sensor. Therefore, at end of the B-2C's sensor life, the lead concentration in the electrolyte solution is at a few thousands ppm level and majority of the lead is still in solid form. 

Sometimes, lead oxide is formed on the anode (note: lead oxide is also in solid form, reddish crystals over the lead). The current generated by the sensor at ppm levels is so low that most of the lead at the end of life is still in solid form. More importantly, at the end of life, the limiting factor is water loss from the electrolyte and not lead consumption.​

A: 0.5 cc of O2 per hour​

A: -1/3 of an atmosphere below atmospheric pressure​

A: A class B-2C cell is just a B-2 with a clamp over the sensing membrane. The specifications are exactly the same. Now that Teledyne has clamped all the trace O2 sensors, a letter C was added to those cells, and we no longer make a class B-2 or A-2 cell. 

The class B-2C cell is the correct replacement sensor for any application that normally requires a B-2 or a B-2C cell. 

In the past this clamp was reserved for applications where the sample gas was lighter than air (like H2 and HE). Due to the mobility of these gases, it was more likely that the membrane would lift and cause a leak at the seams. To prevent that from happening, we added a clamp to strengthen the seal. 

We have since decided to add this clamp to all B-2 cells, and make them all class B-2C. Now this one sensors covers all the trace O2 applications, (except for a CO2 containing sample, which has its own cell class, A-2C).​

A: No, this will damage the sensor. Methyl mercaptan (CH3SH), like H2S, will poison the Micro-fuel Cell cathode. CH3SH is soluble in KOH and forms a lead salt that will deposit on the cathode or membrane. Therefore, we cannot measure O2 in CH3SH by any Micro-fuel Cell. ​

A: The procedure can be found by downloading this PDF file.​

A: Ammonia or Ammonium Hydroxide evaporate / condensate will effect sensor performance. If it condenses on the surface of the sensing membrane, it will block the sensing area making the output erratic. Any condensate over the sensing area will do the same (including water).

Most importantly, Ammonia or Ammonium Hydroxide evaporate / condensation will effect the sensor physically. It will have a corrosive effect, corroding the contact plate. Then the output will decrease or will be erratic. Also, it will react with the adhesive on the sensor label, and label will peel off the sensor.​

A: Teledyne's A-2C and B-2C sensors cannot be used in 1000 ppm SO2. 

If the SO2 is less than 100 ppm, the A-2C may work, but with a lowered life expectancy; maybe 3 months.

SO2 is compatible with the buffered electrolyte in an A-2C, but will form a lead sulfate deposit. If the deposit is formed on the lead anode, there will be no problem, but if it forms at the cathode, the sensor will die. 

SO2 is an acid gas. It reacts with KOH, so the B-2C sensor is also not appropriate. 

An alternative approach is to use a portable analyzer with an A-5 sensor. The O2 level for this application is 1000 ppm. The detection range can be 0 - 1%. At this range, the sensor will recover from air very fast. The A-5 uses a rhodium plated cathode, so it is less likely to form a deposit. ​

A: Chlorodifluoromethane (CHClF2) is a colorless, odorless, non-toxic gas, like CH4 (3 H atoms replaced by 1 Cl and 2 F), but unlike CH4 it is non-flammable. There should be no interference on B-2C for trace O2 measurement.​

A: NOx usually refers to a mixture of NO and NO2. This is because NO is easily oxidized into NO2 if O2 or other oxidizing agents are present.

NOx will interfere with O2 detection by B2C sensors. In theory, 1 ppm NO will reading 0.5 ppm O2.

CO is a carbon oxide, but not necessarily an oxidizing agent. It is normally considered as a reducing agent, somewhat like H2. CO can be oxidized by O2 to form CO2 and produce heat. This reaction is not naturally occurring and must be catalyzed in high temperatures. In fact, CO can be used by a high temperature Fuel Cell (solid oxide fuel cell, SOFC) operated at 1000C to produce electricity. The mechanism of 10% CO produces 1 ppm O2 negative reading is not clear. It is possible that CO may absorbed over the cathode surface to lead the negative output.

NO2 (sometimes as N2O4 if under pressure) is an oxidizing agent. It acts like O2. However, NO is complicated. It can be oxidized by O2 into NO2 (like a reducing agent), but it also can be reduced into N2 (like an oxidizing agent). The redox potential need to be used to judge whether NO will be a reducing agent or an oxidizing agent in an electrochemical environment like in Micro-fuel cell. Because the lead anode is more powerful as a reducing agent than NO does, so NO will be reduced by lead and act like O2 as well in Micro-fuel cell environment. ​

A:

1. CO2 will enter the sensor and react with KOH electrolyte to form a carbonate ion. The electrolyte layer between the sensing membrane and the cathode will change pH due to the neutralization of KOH by CO2. Then, a transition response of the sensor will be observed if the CO2 is very high, such as 100% CO2. Most likely, the sensor will go negative and recover. 

2. When high levels of CO2 continuously enter the cell, lead carbonate will be formed due to the increase of carbonate ion. Lead carbonate will first deposit over the cathode surface and initially cause the sensor to have a high offset. More importantly, as the coating over the cathode becomes heavier, the sensor output starts to drop. 

3. As the lead carbonate continuously forms over the cathode surface, the sensor will lose span due to the coverage of lead carbonate over the cathode surface and the increased thickness of the electrolyte layer between cathode and sensing membrane.

4. As the CO2 continuously enters the cell, it will advance inside the cell and form lead carbonate over the lead anode. A very dense lead carbonate will eventually form a coat over the lead anode. Then there will be no more lead available for a further reaction. At this stage, the sensor will cease functioning.

If the CO2 exposure is not high or continuous, the lead carbonate ion is very low inside the cell and will not form a deposit. A small amount of lead carbonate can re-dissolve when the sensor is exposed to normal air.

The CO2 in air is only 300 to 400 ppm and will not neutralize the 15% KOH and the above reactions. Above 1% CO2, and continuous exposure will lead to the above reactions. If the CO2 concentration is very high, such as 100% CO2, then the sensor can be damaged in a few hours. If the sensor is only in 100% CO2 for a few minutes, then it will be recovered after exposure to air, but the life of the sensor will be seriously reduced. ​

A: An A5 sensor is recommended instead of a B1, B3 or C3 in percent oxygen measurement applications when percentage CO2 gas concentration in the sample gas is high.

An A2C sensor is recommended instead of a B2C in trace oxygen measurement applications when percentage CO2 gas concentration in the sample gas is high. 

A: B-39335​

A: 10k plus or minus 5% would be fine and not substantially effect the tracking of the built in temperature compensation network that is on the sensor. And yes, the temperature compensation is built in.​

A: We recommend calibrating at the highest O2 level that the unit will be used at.

At 100% O2, the output is about 5 times higher than at air (100/20.9 to be precise). Some sensors put out 10mV in air. Then these will put out 10mV*(100/20.9) in 100%.

Some sensors put out 13mV in air. Then these sensors will put out 13mV * (100/20.9) in 100%.

Please understand that these sensors are partial pressure O2 sensors. They respond to changes in the partial pressure of the O2 sample.​

A: The KOH electrolyte can be stored for a long time (years) as long as the bottle has been kept tightly sealed. If the bottle has been uncapped and left open to air, CO2 from ambient air can deteriorate its capacity to work properly. So if the bottle cap has been kept tightly sealed (even after using some of the electrolyte), it can still be used.

Recommendations:

1. Hand tightening the cap and then wrap black electrical tape around the cap/bottle interface to ensure the cap is tightly sealed at all times. 

2. Also, if electrolyte has been stored for 2 years, pre-purging with zero N2 gas (meaning bubbling N2 through the electrolyte) for at least 30-45 minutes before use will help with zero off down time. This will drastically shorten the down time.​

A: The B-2C cannot work in F2. F2 will give the signal as O2.​

A: Generically, Micro-fuel cell sensors -- B-2C, A-2C, etc -- will give a negative reading (approximately -1 ppm for every 10% CO.) This will vary somewhat from sensor to sensor. ​

A: There is only one difference between the R21A and R22A. If you look carefully you will note that the threads on the sensing side of the sensor are different. The R21A has a US thread while the R22A has a metric thread. I am told by customers that the two can be interchanged but I would not suggest it. If a sensor gets cross threaded it could lead to air leaks which in turn could produce incorrect readings.​

A: The B-2C will work in a Dimethyl Ether background as long as it is in vapor form (Non-condensing) and being operated in the normal 0-40 deg C temperature range. ​

A: This means that the signal from the sensor during zero cal was too high. Possible reasons are bad zero gas, a leak in the line, or trying to zero too soon after sensor installation.

My recommendation is that you simply not zero the unit. Do a c​old start of the unit​ and then just do a span calibration but no zero cal. Normally a zero cal is not needed. ​

A: The date code on the sensor is the manufacture date for our internal inventory use. 

The warranty, expected life, and shelf life starts from the date of shipment. It is not determined by the date code. 

The class B1 sensor, for example, has a warranty life of 6 months starting from the date it is shipped from our factory.​​

A: To predict the output of the sensor at 25% O2, please use the formula output at 25% O2 in millivolts = (25.0/20.9)*(output at 20.9% O2 in millivolts).

This would be a range of 9.6 to 15.6 millivolts. ​

A: 

1. The electrolytes in both B3 and B3C cells are the same. The two sensors are manufactured the same except for the installation of the clamp on B3C cells. This electrolyte is used in non-Carbon Dioxide (CO2) background gas applications.

2. A "clamped" cell means that the cell has a circular metal clamp and clamp ring to hold the clamp in place over the front sensing surface. Clamped cells (like the B3Cs) are generally used in "lighter than air gas" applications (for example, hydrogen or helium background gases). In these applications, the front clamp will keep the sensing membrane firmly over the cathode in the cell.

In vacuum applications where the sample gas is drawn in by a vacuum pump, a clamped cell is used. Again, the front clamp will keep the sensing membrane firmly over the cathode.

If there is no hydrogen/helium gas nor a vacuum applied, then the standard B3 cell will work fine.

3. Yes, the B3C will fit inside a B3 cell holder. The probes on the TAI percent O2 analyzers can accommodate both standard or clamped cells. 

A: Our sensors measure the partial pressure of oxygen and are, for most purposes, flow insensitive. What is important is the partial pressure of oxygen in the no flow condition, which is a function of leakage paths, oxygen level, and volume of gas in contact with the cell, and the oxygen profile of the gas that leaks into the measurement system with no flow, and the rate of this leakage. These factors can vary significantly from system to system.​

A: The volume inside the blue cap and between the cap and UFO 130-2 sensor is about 0.119 in^3. ​​​

A: The life expectancy of an R-17 or R-22 oxygen sensor is a function of the integral of the amount of current that flows through the sensor. The sensor is designed to nominally last three years at 20.9% O2 at room temperature.

The amount of current that flows through the sensor is a function of oxygen concentration and temperature. Since the device is linear, doubling the oxygen concentration at the same 25% will reduce the life by a factor of two.

The effect of temperature is such that sensor current goes up by 2.5% per degree C according to the formula Sensor current as a function of

Temp = Io(1+.025)^t-temp at Io, at 40C

This increases the sensor current by a factor of 1.45, so life would decrease due to an elevated temperature by this factor as well.

If you run at 60% oxygen, and 40C, the lifetime instead of three years would be = 3/(1.45*60/20.9))=3/4.16 years = .72 years​

A: Argon and N2 are both completely inert to the sensor. The sensor cannot tell the difference between Argon or N2. They can be calibrated in an N2/O2 mix and then accurately measured in Ar/N2/O2 mixes with no problem whatsoever.

A: The class B2C sensor is intended for use in PPM levels of Oxygen, not percent levels.

You can use it in percent levels of O2, but the life will be shortened, and when exposed to percent levels of oxygen it will no longer be useful in low ppm levels of O2.

So it's OK to use for a temporary fix until you get a percent O2 sensor (like the class B1).​

A: None of these gases, including Helium, will have an effect on the oxygen reading.​

A: Lead oxides have different forms. 

Different lead oxides have different colors 

For instance Pb2O3 is reddish and purple. 

Green is PbO is greenish. 

Pb3O4 is black, or green depending on crystal structure 

Trace amount of zinc or copper in the lead will lead to other colors also. 

Abs cell body may leach out small amounts of chemicals, which cause yellow. 

Trace carbonate will cause white colors.​

A: Please refer to the following document: impact_of_atmospheric_conditions_on_O2_readings.pdf​

A: Methylamine is somewhat similar to ammonia. It will not affect micro fuel cell at ppm level. It may affect gas sample system, such as cell holder, Nylon or SS, O-ring, tube, etc. This gas is a flammable gas, which may need explosion proof if it excess LEL.​​

A: Experience has shown that the sensor will function for months, but lifetime may be reduced. 

Vinyl Acetate may have problem with B2C sensor (KOH based electrolyte). It is not an interfering gas, but may react with KOH to form deposit. A-2C would be better, but we do not have field feedback from this application with the A-2C.​

A: Questions​

1. Can the output of the device be reliably scaled for vacuum throughout the 24 month life of the device? 

We have no data at running under vacuum with this sensor. It is not designed nor tested to run this low. 

Other cells, not UFO, we have run down to 0.2 atm sample pressure, but we cannot say this would apply to this sensor at this time. 

2. Is the relationship of % oxygen to output voltage a linear relationship? If not, has the relationship been defined? 

It is linear to partial pressure of O2 when sample pressure around 1 atm. 

3. Is the device temperature sensitive as well? If so, has the relationship been defined? 

Yes it is temperature sensitive. Both speed and output voltage are temp dependent. The sensor and pcb we sell to go with this compensate both effects to a first order. 

4. How does the output vary with age? Catastrophic or slow decay? 

Output stays reasonably constant with age. Near end of life output is erratic and then dies completely over the course of a few days or less. Sometime it will just suddenly die without erratic behavior. 

5. The device output appears to have a small 2nd order component to it. Has this relationship been modeled? Is this an artifact of circuitry design to effectively speed the response? 

I am not sure precisely what you are referring to here. If u could elaborate on this I could comment better perhaps. 

6. Will the life of the device be adversely affected by operation under vacuum? 

Yes. At low vacuum​ gases in electrolyte will boil out with consequences we have not studied. 

7. Can the life of the device be extended by pinching off the input & output to the device when not in use? 

If you mean but reducing the o2 level, perhaps, but this has not been studied nor confirmed. With no flow, presumably the o2 level the sensor sees will be reduced substantially, but we have not studied the diffusion rate of ambient o2 into the cell under these conditions. 

The more o2 the sensor sees, the quicker it will expire. 

8. I understand that there is FDA regulation on the device some how. Is the device built under GMP? 

I need to check on this matter. We have a 510k on the sensor and we are subject to fda inspections of course, but I am not sure if technically we claim gmp compliance. I need to check with our Qa people.

9. Is the device RoHS compliant? 

No, the device has a lead anode.​

A: The date code is a letter followed by a number. The letter ​corresponds to the month, the number to the year. 

For example, A7 means made in January of 2007. 

D8 means April of 2008​​