Alec Fisher

Publication Date


Document Type


First Advisor

Kocanda, Martin||Ballantine, David Stephen

Degree Name

B.A. (Bachelor of Arts)

Legacy Department

Department of Electrical Engineering


There are a wide variety of circumstances in which knowing of the presence of various potentially toxic gases in the local atmosphere is desirable. For many cases, such as for average household use, inexpensive alarms or detectors are readily available for specific gases. Common examples of these are carbon monoxide detectors and smoke alarms. However, for some applications, a higher degree of precision and detail about the prop­ erties of the local environment is desired. Unfortunately, commercial solutions to this problem are prohibitively expensive for many cases. The purpose of this project was to study the behavior of MQ-series gas sensors. These are metal oxide semiconductor gas sensors which are inexpensive and readily available from internet retailers which makes them seemingly ideal for the entrepreneur or hobbyist looking to work with gas sensors. However, the sensors are not internally calibrated, so characterizing their behavior is nec­ essary before they can used to collect quantitative data. While there are others available, the models tested for this experiment were the MQ2 (flammable gas and smoke), MQ4 (methane), MQ6 (isobutane/propane/LPG), MQ7 (carbon monoxide), and the MQ9 (car­ bon monoxide/flammable gas). The primary goal was to find a relationship describing the sensor signal as a function of gas concentration and the sensitivity resistance. To accomplish this, a testing apparatus was created such that a controlled mixture of a gas to which the sensor is sensitive (propane, referred to generally as the ”active” gas) and an inert gas (nitrogen, generally referred to as the ’’inactive” gas) could be passed over the sensor surfaces. Different combinations of active gas concentration and sensitivity resistor values were explored to develop the desired functional relationship. Upon examination of the results of over one-hundred trials, it was concluded (in accordance with equations derived analytically) that there was a strong relationship between sensor value and active gas concentration resembling a logistic function. Additionally, it was found that the re­ sistance across the sensor itself is strongly dependent on the voltage drop across it and its reference atmosphere, though the nature of said relationships were not determined due to the multitude of potentially influential factors regarding which either little information was available or studying would be prohibitively difficult.


24 pages




Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type