Table 1.

Summary of the definition and formula of sensor parameters

Parameter	Definition	Formula
R a	Resistance value of the device, when put into the dry, clean atmosphere
R g	Resistance value of the device, when put into gas to be detected
S	Ratio of variation of resistance ($\left|R_{\text{a}}-R_{\text{g}}\right|$) to initial resistance (R a)	$S=\left|\frac{\mathrm{\Delta }R}{R_{\text{a}}}\right|\times 100\%=\left|\frac{R_{\text{a}}-R_{\text{g}}}{R_{\text{a}}}\right|\times 100\%$
LOD	The lowest concentration of target gas that can be distinguished from the common atmosphere, which produces a signal greater than three times the standard deviation of the noise level
T res	Period of time from gas sensor contact with gas to be detected to variation of resistance reach to 90 % of $\left|R_{\text{a}}-R_{\text{g}}\right|$
T rec	Period of time from gas sensor away from gas to be detected to variation of resistance reach to 90 % of $\left|R_{\text{a}}-R_{\text{g}}\right|$
D	Ratio of response of target gas (S c) to response of disturbed gas (S i).	$D=\frac{S_c}{S_i}$