Calibration and Implementation of Heat Cycle Requirement of MQ-7 Semiconductor Sensor for Detection of Carbon Monoxide Concentrations

Abstract

Carbon monoxide (CO) is a prevalent and widely distributed air pollutant. Its detection and control in residential and industrial environments are essential in order to avoid potentially severe health consequences in people. The aim of this study was to conduct an air quality assessment by measuring CO concentrations using the MQ-7 Semiconductor Sensor. The MQ-7 sensor is a commonly accessible and cost-effective sensor with specific heating needs. The objectives of the study are to provide a method for implementing heater cycle requirements, equipment-less calibration, and the derivation of a formula for measuring CO concentrations in parts per million (ppm). A procedure for calibrating gas sensors is discussed, which involves measuring the sensing resistance and calculating the resistance ratio. The resistance ratio is then used to calculate the target gas concentration in ppm using a formula derived with the aid of Microsoft Excel, such that it represents the original CO characteristic curve provided in the sensor datasheet with greater accuracy. An N-channel MOSFET and Pulse Width Modulated (PWM) voltage were used to get the required heater voltage levels. The methodology developed for calibrating and deriving the equation to determine the target gas concentration can be used for any MQ semiconductor sensor and does not require any special equipment.