Neotronics Limited

Gareth J Jones

Howard A Buckenham

Paul Gotley

Fault detection in electrochemical gas sensing equipment

Circuits are described in which the sensing and the reference electrodes of a gas sensor housed within a gas monitor are connected together through the source and the drain of a field effect transistor (FET). The gate of the FET is connected to a power source to apply a first voltage to the gate when the monitor is operational and a second voltage, which is preferably zero, when the monitor is not operational, the resistance between the source and the drain of the FET being low when the second voltage is applied to the FET gate so that the sensing and reference electrodes are connected together in a short circuit. When the first voltage is applied to the FET gate, however, the short circuit is effectively broken. The circuit has output lines leading to an output device, e.g. for displaying information or an alarm. A resistor of large resistance is connected between the two output lines and, when a gas is sensed a large voltage change occurs across the resistor which can be used directly, i.e. without an intervening amplifier, for driving the output device. A further, small resistor is connected between the reference electrode and the sensing electrode to provide noise immunity to the circuit.

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Great Abington, United Kingdom

Gareth J Jones