hanwei electronics co. ,ltd mg - 811 http: //www. hwsensor. c om tel: 86 371 5333098 5333099 fax: 86 371 5333090 e - mail: sensor@371.net MG811 co2 sensor features good sensitivity and selectivity to co2 low humidity and temperature dependency long stability and reproducibility application air quality control ferment process control room temperature co2 concentration detecti on structure and testing circuit sensor structure and testing circuit as figure, it composed by solid electrolyte layer ? 1 ?? gold electrodes ? 2 ?? platinum lead ? 3 ?? heater ? 4 ?? porcelain tube ? 5 ?? 100m double - layer st ee less net ? 6 ?? nickel and copper plated ring ? 7 ?? bakelite (8) ? nickel and copper plated pin ? 9 ?? working principle sensor adopt solid electrolyte cell princip le ? it is composed by the following solid cells o air ? au|nasicon|| carbonate|au, air ? co2 when the sensor exposed to co2 ? the following electrodes reaction occurs o cathodic reaction o 2li + + co2 + 1/2o2 + 2e - = li2co3 anodic reaction o 2na+ + 1/2o2 + 2e - = na2o overall chemical reaction o li2co3 + 2na + = na2o + 2li + + co2 the electromotive force ? emf ? result from the above electrode reaction, accord with according to nernst ? s equation: o emf = ec - (r x t) / (2f) ln (p(co 2 )) p(co 2 ) ?a co2 --- partial pressu re ec ?a constant volume r ?a gas constant volume t ?a absolute temperature ? k ? f ?a faraday constant from figure 1b ? sensor heating voltage supplied from other circuit , when its surface temperature is high enough , the sensor equals to a cell, its two side s would output voltage signal ,and its result accord with nernst ? s equation ? in sensor testing, the impedance of amplifier should be within 100 ?a 1000g |? ? its testing current should be control below 1pa. figure 1a figure 1b figure 1a
hanwei electronics co. ,ltd mg - 811 http: //www. hwsensor. c om tel: 86 371 5333098 5333099 fax: 86 371 5333090 e - mail: sensor@371.net specifications o symbol parameter name technical remark s v h heating voltage 6.0 0.1 v ac or dc r h heating resistor 30.0 5% |? room temperature i h heating current @200ma p h heating power @1200mw tao operating temperature - 20 ?a 50 tas storage temperature - 20 ?a 70 ? e ?? m f output 30 ?a 50mv 350 ?a 10000ppmco2 sensitivity o figure 2 shows gas sensor sensitivity curve. o conditions: tem o 28 ??? rh o 65% ? oxygen o 21% emf: sensor emf under different gas and concentration . response and resume characteristic o figure 3 shows solid electrolyte sensor response an d resume characteristics. temperature and humidity dependency o
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