Coulomb electricity sensor and electrochemical tra

2022-09-21
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The difference between Coulomb electricity sensor and electrochemical sensor used in isobaric oxygen permeating instrument

the international standard ISO, ASTM d3985 and Chinese national standard gb/t 19789 all require the use of Coulomb electricity sensor, and clearly states that the Coulomb electricity sensor is an absolute value sensor without calibration. But in the market, there is still a way to use electrochemistry. Do you know the role of pulse fatigue testing machine? The detection accuracy and stability of the oxygen permeameter with the Coulomb electric quantity sensor cannot be compared with that of the Coulomb electric quantity sensor. The following is the analysis and introduction of these two sensors:

first, the Coulomb electric quantity sensor

1. The Coulomb electric quantity sensor is an internationally recognized absolute value sensor

the Coulomb electric quantity sensor conforms to Faraday's law. Every time an oxygen molecule enters, it will release four electrons, and the output efficiency is as high as 98%, This linear proportional relationship is not affected by osmotic concentration and environmental changes of the sensor

2. The Coulomb electricity sensor detects 100% of the oxygen penetrated, and no one is missed

3. The Coulomb sensor does not need calibration.

usually, it only needs to accurately control the test environment of the sample, such as temperature and humidity, flow, reference noise and other parameters. The standard membrane with NIST effective traceability provided by MOCON can be used to verify the oxygen permeating instrument rather than calibrate it

4. The Coulomb absolute value sensor is not affected by ambient temperature, sensor temperature and carrier gas flow rate

5. The Coulomb electric quantity sensor has a long service life

it can be used for 5 years under normal continuous high barrier test

5. Only MOCON's oxygen permeameter adopts a real Coulomb absolute value sensor

only MOCON's oxygen permeameter truly meets the requirements of ISO, ASTM d3985 and gb/t 19789 standards, and its high accuracy and reliability are universally recognized

II. Electrochemical sensor:

1. Electrochemical sensor is a relative value sensor

in order to prolong the service life of the sensor, the outer layer of the electrochemical sensor is coated with a soft membrane. Only a small part of the oxygen infiltrated from the sample can pass through this soft membrane, and finally enter the sensor to generate an electrical signal. The existence of this soft membrane makes the infiltration process twice, making the sensor a relative value sensor, which cannot output an electrical signal linearly according to the number of oxygen molecules

2. The electrochemical sensor only detects a small part of the infiltrated oxygen

however, most of the infiltrated oxygen is directly discharged from the bypass and has not been 100% detected. Changes in the permeability of the soft membrane itself (such as aging, temperature changes, etc.) directly affect the accuracy of the test

3. The electrochemical sensor needs to be calibrated and compensated by different concentrations of oxygen

however, because the electrochemical sensor only detects part of the oxygen and cannot achieve linear output, it is still unable to guarantee the full range accuracy by using only several concentrations of oxygen for calibration. As long as the oxygen permeameter needs calibration and compensation, it uses electrochemical sensors that do not meet the standard requirements

4. The electrochemical sensor will be affected by the ambient temperature, sensor temperature and carrier gas flow rate

because the sensor is located in the chassis of the instrument, the sensor temperature will change with the ambient temperature, and the oxygen permeability of the soft film itself will also change, so the sensor test accuracy is easily affected by the change of ambient temperature. Generally, the ambient temperature of standard laboratories fluctuates between 4~5 ℃ (± 2~3 ℃), which will bring more than 0.5cc/m2day drift to their sensors, which will have a great impact on the test data of high barrier materials

5. The service life of electrochemical sensor is short

under normal continuous high barrier test, the service life is only about one year

6. The electrochemical sensor was not recognized by ASTM Standards Committee

according to the data comparison test presided over by ASTM Committee, especially when measuring materials with low transmittance, its test results will have great deviation, which cannot meet the requirements of ASTM d3985. The final conclusion of the ASTM committee is to maintain the requirements of the ASTM standard for Coulomb electricity sensors

3. MOCON provides a standard membrane that has not been able to overcome ist in traceability n batch quantification or large-scale production to verify the equipment

mocon uses absolute value sensors that do not need calibration, and the output result is completely linear. However, MOCON can still provide standard films traceable to n.i.s.t. to customers as a selective verification means, which users can use when they need to verify instruments. There are three different orders of magnitude for standard membranes. As long as the measured values of these three standard membranes are within the allowable error range, according to the linear relationship, the instrument can be guaranteed to be in the best state and achieve the test accuracy in the full range. In daily work, users only need to use the film closest to the usual test range

the oxygen permeability of other manufacturers can also be used for the experimental instruments of the compressive strength of other non-metallic materials. Because they use the relative value sensor, they must use the standard film for calibration and compensation. Using three standard films, in fact, they can only calibrate three oxygen concentration gradients, which is just the calibration of three points on a curve completed by Harbin Institute of technology and China Air Force Research Laboratory, Since there is no linearity, this calibration is invalid for other points within the full scale range. For these three calibration points, after compensation, use the same film for verification. The accuracy of the verification results does not represent the accuracy of other points. (end)

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