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August 2017
DocID025166 Rev 2
1/27
www.st.com
AN4348
Application note
Signal conditioning for electrochemical sensors
Pierre Sennequier
Introduction
Unmonitored gas can rapidly become a danger. Consequently, in many industries such as refining,
mining, and semiconductor industries, monitoring air quality is mandatory for security reasons. Gas
monitoring is also important in parking lots and in connection with domestic use. For example,
thousands of people are killed every year by carbon monoxide poisoning due to bad combustion.
For these reasons, different gas sensor technologies exist. Of these, the electrochemical sensing
technique has the advantage of having a linear output and operating with a low consumption.
Consequently, it operates on batteries for a long period of time (particularly true for the toxic gas sensor
which delivers almost no current in ambient air), and therefore is used for portable personal protection
equipment.
The gases most frequently monitored by handheld safety detectors which use electrochemical sensors
are oxygen (O
2
), carbon monoxide (CO), hydrogen sulfide (H
2
S) and nitrogen dioxide (NO
2
). However,
many other gases can also be monitored with electrochemical sensors.
Electrochemical sensors are widely used in the medical sector. For example, to monitor the
concentration of glucose in the blood of diabetic patients, a glucometer (glucose meter) is used. In this
case, the disposable test strips are the electrochemical sensors. Figure 1 illustrates the carbon
monoxide and the glucometer test-strip sensors.
Figure 1: Electrochemical carbon monoxide sensor and glucometer test strip
Electrochemical sensors can also be used in agriculture (to control fruit ripening), the automotive
industry (or any activity requiring a combustion control), and for diving and medical reasons.
