Frequently Asked Questions
What type of sensor technology does Analytical Industries Inc., dba Adavanced Instruments, use for measuring oxygen?
Electrochemical, specifically a galvanic type oxygen sensors.
What is the difference between trace and percent measuring ranges? Do you offer both?
Typically, trace PPM oxygen analyzers are recommended for measuring oxygen concentrations below 1,000 PPM (0.1%) whereas percent analyzers are better suited for higher oxygen levels. Trace PPM and percent analysis ranges overla somewhat between 1,000 PPM (0.1%) and 1% with the user’s long term need usually being the determining factor in selecting an analyzer. We specialize in both trace PPM and percent range analysis, and, offer PPB and purity oxygen analyzers as well.
What materials are used to manufacture the oxygen sensor?
Teflon membranes heat sealed to a HDPE body encapsulate anode, cathode and electrolyte. The “GPR” and “PSR” series sensor electrolyte is (base pH) consisting of mostly water. The “XLT” series contains a proprietary acid bases electrolyte. Wire conduct outputs from anode (-) and cathode (+) inside the sensor to soldered termination on a PCB (with resistor- thermistor temperature compensation network) heat sealed to the outside of the sensor.
Can sensor be contaminated by carbon dioxide (C0²) gas, reducing the sensor life?
Exposure of the GPR/PSR sensor with its base electolyte to carbon dioxide (CO²) gas or acid gases, produce crystal-like deposits on the cathode which reduces the surface area of the cathode and the corresponding signal outputs. This effect is cumulative, cannot be reversed and can dramatically reduce the expected sensor life. The solution: Analytical Industries Inc. offers an optional “XLT” sensor for use in 0.5%-100% CO² with our Advanced Galvanic Fuel Cell (sensor) PPM series, and Percent series. We also manufacture “XLT” equivalent replacement oxygen sensor when properly installed and operated. Refer to the individual analyzer and transmitter specification sheets to see if an “XLT” model is available for that particular configuration, or check the Replacement Sensor Guides for replacement options.
How does the oxygen sensor operate?
The galvanic fuel cell sensor is an electrochemical transducer which generates a current (µA) signal output, primarily from the cathode that is both proportional and linear to the partial pressure of oxygen in the sample gas. The sensor has an inherent absolute zero, therefore, no oxygen no signal output. Oxygen diffuses through the front sensing membrane simultaneously contacting anode, cathode electrolyte to activate the cathode or sensing electrode.
What is the oxygen sensor signal output?
Historically specified as a normal value +-30% in air (20.9% oxygen) at 25°C (77°F) and 1 ATM. The normal value is based on the thickness or diffusion rate of the front sensing membrane. The +- 30% allows for variations in the membrane (a lamination process) and heat sealing process. The above PCB network converts the signal output from current (µA) to (mV) signal output. Component selection can narrow the (mV) signal output range. Signal output can be influenced (and compensated) by several factors. Except as noted in #15 below, a higher or lower signal output offers no performance advantage.
What is the recommended temperature range of the oxygen sensor?
Check the sensor label, product specification, or owner’s manual to determine what sensor model you are currently using. GPR series sensor, 0°C (32°F) to 50°C (122°F)
How does change in temperature influence the oxygen sensor’s performance?
Temperature influences the signal output at the rate of 2.54% per °C. Ambient (gradual) changes in temperature can be maintained within +-2% accuracy specification by processing the signal output through an appropriate resistor – thermistor temperature compensation network, see#3 above. Step (rapid) changes of 15°C (59°F) require 45-60 minutes for the compensated signal output to equilibrate, e.g. the electronic thermistor reacts immediately to offset the change in the sensor (sensing membrane and electrolyte) which reacts at a much slower rate, e.g. ice melting. OEM manufacturers are compensating for temperature electronically which eliminates the stabilization period related to rapid temperature changes.
What is the pressure required for optimum analysis?
The recommended pressure range is 5-30 PSIG, up to 100 PSIG, with a flow rate of 1-2 SCFH.
How does pressure influence the oxygen sensor’s performance?
Pressure influences the signal output on a proportional basis. The sensor is accurate at any constant pressure up to 30 ATM provided the sensor (front and rear membranes) is presssurized and decompressed gradully (similar to human lungs). The membranes, especially the front sensing membrane, do not tolerate rapid change in back pressure or vacuum. Typical recommendation to protect the sensor is a vacuum less than 14″ WC. Caution: Using one’s finger to block the vent to confirm flow creates backpressure on the sensor and when removed draws vacuum on the front sensing membrane resulting in torn membrane (possible leak of eletrolyte) or in erratic readings if the membrane remains intact.
What is the maximum altitude the oxygen sensor can be exposed and still function?
Oxygen sensors have been tested and performed up to 20,000′ with no error. The oxygen sensors are undergoing further testing up to 40,000′. In 2007, Analytical Industries Inc. oxygen sensors were used in the Caudwell Extreme Everest expedition taking our sensors up to 32,000′ to the tip of Mt. Everest in a modified heated rebreather circuit.
Does moisture or water affect the oxygen measurement?
If moisture or water is present in the gas stream it will not damage the oxygen sensor or analyzer, but it will collect on the sensor’s sensing membrane, thus, block the flow of gas. If moisture or water does get in the gas sample line we suggest removing the oxygen sensor and dab with a terry cloth to dry and, or flow air or span gas through the analyzer to clear out any residual moisture or water in the analyzer sample system. Once the sensor and the analyzer sample system are dry, both will resume functioning properly. Caution: If water is left inside the analyzer corrosion can occur. If this is the case, contact the factory for further instruction. If moisture is in the sample gas, we can recommend and supply a suitable coalescing filter depending on the volume of moisture or water present.
Does humidity affect the oxygen measurement?
If the humidity is present in the sample gas stream and is non-condensing, there is no affect on the oxygen measurement. If condensed, refer to #12 above.
Are your oxygen sensors resistant to H²S
Analytical Industries Inc. offers H²S scrubbers that effectively remove H²S from the sample gas if present. Contact factory for suitable sample gas conditioning system gas if present.
What is the expected oxygen sensor life?
Refer to the individual specifications to determine the estimated life of the oxygen sensor. In theory, a higher signal output yields a shorter life because the anode is being consumed at a faster rate. In reality, however, the expected life specifications considers the upper limit (+30%) of the signal output range. Sensor life is inversely proportional to changes in oxygen concentration, temperature and pressure. Refer to #6 above.
Is there a maximum load for the oxygen sensor?
The sensor does not tolerate reverse current flowing into the sensor. Maximum load is a flat 10K, no load is recommended. Increasing the load over 10K maximum produces an error in linearity.
What is recommended calibration gas?
Depending on the analysis range, please refer to the following for general recommendation. Pico-Ion UHP PPB Sensor, Pico-Ion MS PPB Sensor, and Advanced Galvanic PPM Series: Certified gas oxygen balance N2 approximating 80% of range above analysis range recommended for optimum results. Advanced Galanic Percent Series- Ambient or compressed air on 0-25% range; or certified span gas of oxygen balance N2 approximating 80% of range above analysis range recommended for optimum results.
How often should I calibrate my oxygen analyzer?
Recommend at least every 2-3 months, or according to the process requirements.
When measuring trace oxygen, can I use plastic tubing to deliver the sample to analyzer?
Due to the permeability factor when using plastic, we do not recommend for trace analysis. Whenever possible, stainless steel tubings and fittings should be used to avoid a leak. Ambient air contains 209,000 PPM (20.9%) of oxygen, and use of plastic sample tubing may introduce a leak for outside air contaminting the sample gas.
When an oxygen sensor is nearing the end of its useful life, how do I know when I need to order a replacement oxygen sensor?
Complete oxidation of the anode characterized by a sharp decrease in signal output during the last 5-10% of service life which prevents calibration of the electronics (the signal output falls below the lower limit designed into the electronics). See #6 and #15 above.
The oxygen sensor has been exposed to liquid, and it is no longer working. Does the oxygen sensor need to be replaced?
The collection of condensation on the sensing surface of the sensor reduces the signal output and is mistakenly catergorized as a sensor defect, when in fact it is the law of physics. The reality, remove or dry the water and the signal output returns. See #12 above. For example, a thin layer of water over the sensing surface will reduce the signal output of a sensor from 11.8mV to 10.1mV in 20 minutes; dump the water and the signal output returns to 11.8mV in 30 seconds. Note: Water, particularly salt water in diving applications, can corrode or bridge electrical connections (unless waterproof by conformal coating) resulting in erratic oxygen readings.
Can the oxygen sensor be damaged if it has been dropped?
Dropping a sensor that has been removed from its shipping package can damage the sensor in a number of ways: (a) broken wires; (b) broken electrical connections; (c) dislodging the anode and either breaking a connection or creating an internal short as the loose anode comes in contact with the cathode connection. For example, dropping a sensor from 3′ onto a carpeted concrete office slab results in a 25-100% reduction in signal output
The oxygen sensor is giving erratic readings, what is the reason?
Erratic oxygen readings can be due to: (a) compromised electrical connections (see #20 above); (b) blocking the “breather holes” on the PCB at the rear of the sensor prevents the pressure surrounding the sensor (front and rear membranes) for equalizing; (c) a load in excess of 10K ohm (see #16 above); (d) sudden vacuum draw on the sensor, e.g. using one’s finger to block the vent to confirm flow creates backpressure on the sensor and when removed draws vacuum on the front sensing membrane resulting in erratic readings if the membrane remains intact (see #10 above).
The oxygen sensor is reading high, what is the reason?
High oxygen readings can be due to: (a) step (rapid) changes of 15°C (59°F) or more, see #8 above, require 45-60 minutes for the compensated for the signal output to equilibrate; (b) the amount of oxygen entering into the sensor increase due to sub-microscopic pin holes in the laminated front sensing membrane resulting from; (i) a third party (supplier) manufacturing defects acerbated by high temperature; (ii) mishandling during assembly (possible but unlikely see Quality Control section); (iii) pressing on the sensor surface (out of curiosity or in an attempt to remove liquid). If the membrane is torn as a result of a vacuum suddenly being drawn on the front sensing membrane, a temporary high oxygen reading generally precedes a drop in signal output due to loss of electrolyte.
What is the recommended storage temperature?
The oxygen sensors, when stored, should be kept in a cool or ambient environment to ensure the life upon use.Prolonged exposure above 50°C (122°F) can adversely affect: (a) the sealing of the front and rear membranes to the sensor; and, (b) acerbate any sub-microscopic pin holes in the laminated front sensing membrane, both of which result in electrolyte leakage in the shipping bag. Refer to #8 above. An increase in temperature above 25 °C (77%°F) reduces the expected sensor life because the membrane expands with temperature allowing more oxygen to diffuse into the sensor thereby increasing the rate at wich the anode is consumed.
How long can I store an oxygen sensor in its original shipping container prior to use?
We recommend not to store the GPR/PSR series sensors beyond (6) months, and the XLT series sensors for (2-3) months, for optimal performance.Analytical Industries Inc. maintains a majority of sensors in stock (rotates stock to ensure product quality), available for immediate delivery.
How is your design of the oxygen sensor different from your competitors using the same technology?
After years of accumulated experience working with and studying competitive galvanic oxygen sensors, we have focused on advancing the quality and reliability (along with performance) of our sensors by simplifying the assembly process and eliminating sources of internal contamination. As a result, there are on welds, epoxy or dissimilar metals inside the Analytical Industries Inc. oxygen sensor.
How do you avoid contamination from supplied parts and employees?
In an effort to minimize external contamination from suppiers and employees, critical internal components undergo a propietary cleaning process before assembly commences. With respect to the human element, hand lotions are prohibited throughout the facility. Single approved hand soap is available for washing after every break.
Is there any testing done on the sensors to ensure they are not leaking prior to shipping?
To detect sub-microscopic pin holes in the laminated front sensing membrane resulting from third party manufacturing defects and/or mishandling during assembly, 100% of the base electrolyte sensors are subject to a stringent proprietary procedure desgined to weed out obvious leaks.
Do you test the oxygen sensor signal output prior to shipping?
Following the leak test, 100% of the sensors sit for a predetermined period of time to allow the signal output to stabilize. Next, the current output (µA) of every sensor is tested and recorded. Depending on the sensor configuration, sensors with just a contact PCB (industrial) are tested twice, and sensors with temperture compensation network are tested four times before being accepted and serialized.Diving and Medical oxygen sensors receive proprietary testing based on application.
Are your products date coded?
Oxygen sensors have a finite life. Understanding the date code is vital to getting the benefit of the warranty period, which applies to analyzers and monitors, as well as sensors. The warranty period starts with the date shipped from the factory. Example, the serial number 90734789 breaks down as follow: Digit #1 a (9) denotes the year of manufacture as 2009; digits #2, #3 (07) indicate July as the month of manufacture; the remaining digits are sequential for uniqueness. As the result of a number of issues related to the use of aged sensors, Analytical Industries Inc. plans to add this definition to the sensor’s labeling along with the recommendation that sensors be purchased within 6 months of the manufacture date.
How much hydrogen sulfide (H2S) can the XLT-12-333 and XLT-12-123 oxygen sensors withstand without serionsly affecting the sensor’s expected service life?
We recommend using a scrubber when H2S is known to be present at concentrations above 20 PPM in the sample gas. H2S itself goes not have as effect on the sensors signal however, its corrosive properties will physically damage the sensor over time.
After installing a new sensor, how long can I expect to wait before a calibration can be performed?
The stabilization (or recovery) time of a newly installed sensor will vary with the duration the sensor was exposed to ambient air. Minimizing this exposure will shorten the recovery period. Using UHP nitrogen, our trace oxygen sensors will typically recovery to less than 10 PPM in about 1 hour after being exposed to ambient air for 3 minutes.
How do I know when it’s time to change my H2S scrubber material?
The scrubber media supplied with our H2S scrubbers are of the Potassium Permanaganate type. This material will transition from Purple (new), to Brown (good), then Beige (marginal). Once the material becomes Grayish-White (consumed) in 25% of the column, it is time to change out the media.
After a day of measurements, my GPR-1200 reading rise from low PPM to >10,000 PPM (1%) while in bypass. What is wrong?
The oxygen reading while the analyzer is in bypass mode is known as the “static value”. If the analyzer has been properly purged down with a low oxygen gas (N2 or sample) the norminal static value should be less than 400 PPM. A value in the thousands of PPM or higher indicates a leak in the system. In many cases this can br resolved by checking and tightening loose fittings, but in some cases it would be best to send the unit back to the factory for evaluation and repair.
My GPR-1200 does not charge while it is powered down. What is wrong?
The GPR-1200 charging circuit requires the analyzer to be turned on while charging. Doing this does not affect the sensor performance or service life however; it does allow users to continue working while the unit recharges.
How do I determine the manufacture date of my sensor?
The first three digite of the sensors’ serial number can be used to determine its manufacture date. – The first digit identifies the year (1=2011, 0=2010) – The second and third digit make up the month (02= Febuary, 11= November).
Why would the reading displayed by the LCD not change when the oxygen level changes?
The sensor might be nearing the end of its useful life and must be replaced
Can I use the GPR-11-32 RT sensor in my GPR-2000 instead of the GPR-21 RT?
The GPR-11-32 RT and the GPR-11-21 RT are not interchangeable in the GPR-2000. These sensors exhibit different output, reaponse times, as well as, warranty period. The GPR-2000 electronics are configured to the specific sensor at the time of purchase and manufacture.
I find it difficult to work with stainless steel tubing lines on my portable GPR-1200, can I use plastic instead?
Stainless steel tubing is always recommended for use in trace oxygen measurements due to its non-permeable properties and the quality of the seal achieved with compression fittings. There are however, high pressure nylon or PEEK tubing available in the market that have been tested to hold oxygen permeation and leakage levels to well below 1 PPM.
What are the parameters of your 18 month warranty?
The warranty specification of 18 months is based on the application conditions in the medical field. Generally 40-70% oxygen concentrations are the norm for ventilators and anesthesia machines. An oxygen concentration (62.7%) 3 times that of air (20.9% oxygen) at 25° C and 1 ATM. reduces the expected life (60 months) by a factor of 3 computes to 20 months. Allowing a 10% marginal of error equals our 18 month warranty.We assume the same average for periods where patients are flushed with 100% oxygen and the equipment is not being used and the sensor is exposed to ambient 20.9% ambient.
What is the expected life, storage life, and the extending life of the sensors?
< 6 months at 25° C, from factory ship date to obtain the 60 months expected life in air.Note: The storage life can exceed the 6 months and or the temperature can exceed the 25 ° C (up to 40° C), but in either case the expected life will be reduced.
Warranty Return Policy?
Analytical Industries Inc. will replace any product (sensor or analyzer) within the warranty period specified that is determined by Analytical Industries Inc. to be defective as to materials or workmanship in normal use as defined by the applications specified. Warranty determinations require the product to be returned to the factory for evaluation. However, Analytical Industries Inc. may, at our discretion, waive this requirement. The purpose here is to maintain customer goodwill (a sensor at no charge) yet reserve the right to prevent abuse of our generosity.
Can I pay with a credit Card?
We accept all major credits cards… However, Analytical Industries Inc. will only accept wire transfers for orders going international.
What should I do if a zero reading on the analyzer or ventilator LCD is displayed?
Check sensor and cable connection. Make sure you are using the correct sensor. There are sensors that look alike but the mV outputs or the response times are different, and are not compatible with one anothers equipment. e.g AII-11-60, PSR-11-77 and PSR-11-58 all have a telephone jack but are not compatible with each others equipment Try another sensor in the same piece of equipment and or try the same sensor in another piece of equipment and see if the problem persists.
If the Ventilator or Analyzer will not Calibrate to 100% with the sensor in 100% dry oxygen, I should?
Wait 10 minutes and repeat calibration procedure. Check sensor and cable connection. Check the integrity of gas delivery system, front o’ring seal, quality of gas tested, verify there is no moisture covering the sensor, verify flow rate is between 4 and 5 Ipm Replace sensor and or cable and repeat calibration Try another sensor in the same piece of equipment and or try the same sensor in another piece of equipment and see if the problem persists.
How can I confirm if the drift displayed on the LCD during calibration is caused by the sensor or the equipment?
Let the sensor sit in the holder in room air for at least 10 minutes before calibrating. Check the integrity of gas delivery system, front o’ring seal, quality of gas tested, verify there is no moisture covering the sensor, verify flow rate is between 4 and 5 lpm. Check for leaks around the holder or hoses connected to the exhalation block. Try another sensor in the same piece of equipment and or try the same sensor in another piece of equipment and see if the problem persists.
What should I check or do if the reading drifts 4-5% after calibration in 100% oxygen?
Check primary oxygen delivery service. Replace the sensor. Try another sensor in the same piece of equipment and or try the same sensor in another piece of equipment and see if the problem persists.