Datsheet-based calibration study of the MQ-135 sensors for carbon dioxide (CO₂) and MQ-8 sensors for hydrogen (H₂)

Abstract This research conducted a datasheet-based calibration study using the MQ-135 sensor and MQ-8 sensor to measure carbon dioxide and hydrogen. The process of digitizing datasheet graphs into numbers that have a relationship between electrical quantities and physical quantities (R versus ppm) is carried out using webPlotDigitizer software. Based on the calculation results, a trendline of the power equation model has been obtained for the MQ-135 gas sensor and MQ-8 gas sensor respectively from the comparison of the x -axis (ADC) and y -axis (PPM), namely <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">y</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">MQ</mml:mi> <mml:mo>−</mml:mo> <mml:mn>135</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>7</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">x</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3.108</mml:mn> </mml:mrow> </mml:msup> </mml:math> with a value of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">MQ</mml:mi> <mml:mo>−</mml:mo> <mml:mn>135</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>0.9968</mml:mn> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">y</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">MQ</mml:mi> <mml:mo>−</mml:mo> <mml:mn>8</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>2533</mml:mn> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">x</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.746</mml:mn> </mml:mrow> </mml:msup> </mml:math> with a value of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">MQ</mml:mi> <mml:mo>−</mml:mo> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>0.9875</mml:mn> </mml:math> . Based on the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">R</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> value or coefficient of determination for each sensor, it shows that the value is close to 1, so this shows that the trendline of the power equation model used matches the sensor datasheet. The equations <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">y</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">MQ</mml:mi> <mml:mo>−</mml:mo> <mml:mn>135</mml:mn> </mml:mrow> </mml:msub> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">y</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">MQ</mml:mi> <mml:mo>−</mml:mo> <mml:mn>8</mml:mn> </mml:mrow> </mml:msub> </mml:math> will then be entered into the Arduino IDE program as calibration values for the MQ-135 sensor and MQ-8 sensor to obtain measurement values that are in accordance with the standardized datasheet. To improve accuracy, calibration was also performed using a reference instrument, a Carbon Dioxide Detector for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">CO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> and a C-200 Pen-Type Water Quality Meter for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> , with average errors of 1.29488% and 29.81805%, respectively. The low error value for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">CO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> indicates good compliance, while the high error for <mml:math xmlns:mml="http://www.w3.org/1998/Math