3.5. Signal conditioning of the sensing element for CO2 gas detection with Y2O3-doped CeO2 sensitive material

The operational amplifier ADA4627-1, provided by analog devices (Figure 16) is a broadband and high precision amplifier. It is recommended in applications like "sensor conditioning" and electronic conditioning of the signal, due to its exceptional attributes: low noise, very low offset voltage, very high common-mode rejection ratio (CMMR) and very high slew rate. This operational amplifier combines the best "DC" features and very good dynamic characteristics Prototyping a Gas Sensors Using CeO2 as a Matrix or Dopant in Oxide Semiconductor Systems http://dx.doi.org/10.5772/intechopen.80801 75

Figure 15. The sensor voltage function with CO2 concentration, for T = 20C and two relative humidity testing 40% RH and 80% RH, respectively.

<sup>O</sup><sup>2</sup>� <sup>þ</sup> CO<sup>2</sup> ! CO<sup>2</sup>�

The carbonates disappear when they are exposed to oxidizing conditions [31]. The sensor characteristic was performed using test installation presented in Figure 4. The sensor was exposed at CO2 atmospheres in the concentration range of 0–5000 ppm CO2 in the climatic conditions: T = 20�C and two relative humidity testing 40% RH and 80% RH, respectively. The sensor functions at 135�C, temperature provided by the heating resistance (Figure 9, Pos. 7). Figure 15 shows the variation of sensor voltage with the gas concentration. The characteristics show a slow linear decreasing of voltage with CO2 concentration which allows an easy signal conditioning. In the concentration range 0–5000 ppm CO2, the sensor presents a voltage variation as follows: 378.17–377.32 mV for T = 20�C, RH 40% and 377.11–376.61 mV for T = 20�C, RH 80%. The sensor data show a little dependence of voltage with relative humidity that makes usable in environment with high relative humidity. The sensitivity of the sensor

3.5. Signal conditioning of the sensing element for CO2 gas detection with Y2O3-doped

The operational amplifier ADA4627-1, provided by analog devices (Figure 16) is a broadband and high precision amplifier. It is recommended in applications like "sensor conditioning" and electronic conditioning of the signal, due to its exceptional attributes: low noise, very low offset voltage, very high common-mode rejection ratio (CMMR) and very high slew rate. This operational amplifier combines the best "DC" features and very good dynamic characteristics

was 0.3 V/ppm and the response time was less than 30 s [44].

Figure 14. SEM images for oxidic powder CeO2-Y2O3 calcined at 800�C for 2 hours.

CeO2 sensitive material

74 Cerium Oxide - Applications and Attributes

<sup>3</sup> : (8)

Figure 16. The electronic module for signal conditioning provided by sensing element, designing with ADA4627-1 analog devices.

[33], like: slew rate 60 V/μs; extended range of differential supply voltage: �5 Vcc …. � 15 Vcc; opn loop gain 120 dB; low offset voltage maximum 200 μV and the bias current: maximum 5 pA.
