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Monox Compact-S CO Sensor Cell

Top
Top

Here is an old electrochemical type carbon monoxide detector cell, from Monox. Hole in the centre is the inlet for the gas under test.
DO NOT TRY THIS AT HOME! Electrochemical cells contain a substantial amount of sulphuric acid, strong enough to cause burns.

This is a type of fuel cell that instead of being designed to produce power, is designed to produce a current that is precisely related to the amount of the target gas (in this case carbon monoxide) in the atmosphere. Measurement of the current gives a measure of the concentration of carbon monoxide in the atmosphere. Essentially the electrochemical cell consists of a container, 2 electrodes, connection wires and an electrolyte – typically sulfuric acid. Carbon monoxide is oxidized at one electrode to carbon dioxide while oxygen is consumed at the other electrode. For carbon monoxide detection, the electrochemical cell has advantages over other technologies in that it has a highly accurate and linear output to carbon monoxide concentration, requires minimal power as it is operated at room temperature, and has a long lifetime (typically commercial available cells now have lifetimes of 5 years or greater). Until recently, the cost of these cells and concerns about their long term reliability had limited uptake of this technology in the marketplace, although these concerns are now largely overcome. This technology is now the dominant technology in USA and Europe.

Rear
Rear

Rear of unit with connection pins. Hole here is to let oxygen into the cell which permits the redox reaction to take place in the cell when CO is detected, producing a voltage on the output pins.

Disassembled
Disassembled

Cell disassembled. The semi-permeable membrane on the back cover can be seen here, to allow gas into the cell, but not the liquid electrolyte out. Cell with the electrodes is on the right, immersed in sulphuric acid.

Platinum Electrode
Platinum Electrode

Closeup of the electrode structure. Polymer base with a precious metal coating.

Membrane
Membrane

Membrane & filter on the test gas input port.

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4Warn Carbon Monoxide Alarm

Front
Front

This is an old CO alarm, which was totally dead, having been connected to the wrong PSU.
Here is the front of the unit, with the Test button & indicator LEDs.

Overview
Overview

Front of the PCB, 3 1.5v cells powered the unit, Piezo sounder & sensor cell in the centre of the board.

PCB Rear
PCB Rear

Rear of the PCB with the detection logic.

Sensor
Sensor

Sensor cell. Electrochemical type.