Abstract: A circuit is described which tests whether an amperometric electrochemical gas sensor monitoring the concentration of toxic gases in an atmosphere is working properly. The sensor has a sensing electrode, a reference electrode, and a counter electrode and in normal operation the potential between the reference electrodes is fixed by means of an operational amplifier. When there is gas in the atmosphere, the gas reacts electrochemically at the sensing electrode, causing the amplifier to supply electrical current to the counter electrode which results in an electrical potential to the sensor that is proportional to the amount of toxic gas in the atmosphere. The sensor is periodically tested to determine whether it is working properly by applying a pulse potential between the sensing and reference electrodes. If a current flow results then a signal is sent to an alarm device.

Abstract: An electrochemical gas sensor for detecting the amount of a gas or vapor in an atmosphere is described having a sensing electrode and a barrier limiting the rate of access of the gas or vapor to the sensing electrode, the barrier being made of ceramics material and having an inwardly-tapering shape.

Abstract: 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.

Abstract: This disclosure relates to apparatus of the kind suitable for taking spot measurements of the heat loss or stack loss and/or efficiency (.eta.) in flue gases (stack loss) and comprises respective sensors (5, 3) for producing output signals which vary with the temperature and the concentration of a constituent gas e.g. O.sub.2 of the flue gases and microprocessor-based computation means (10) arranged to derive measurement values of (and numerically equal to) the measured temperature and constituent gas concentration, from the two sensors and to apply these measurement values in the computation of a predetermined formula relating the stack loss or efficiency to the measured quantities. In accordance with the invention, the apparatus is arranged to automatically calibrate each sensor signal from a test measurement prior to deriving the measurement values.

Abstract: A gas detecting device e.g. for detecting CO.sub.2 in air, has a vessel containing water and a layer of ion-exchange resin wetted by the water and sandwiched between air and water-permeable electrode gauze discs. Any CO.sub.2 in the ambient atmosphere dissolves in the water and the dissociated ions lower the resistance between the electrodes which may be connected to a bridge circuit adjusted to be out of balance at a predetermined CO.sub.2 concentration or which may be of dissimilar metal to form a galvanic cell with a measurable output current at a predetermined CO.sub.2 concentration.

Abstract: Apparatus for detecting combustible gases and vapors, and comprises catalytic sensors selectively sensitive to the presence in a given environment of a potentially dangerous constituent such as a hydrocarbon gas and arranged to produce a signal representative of the presence of the constituent, a normally deactivated transducer responsive on activation to the output of the sensors and effective to produce an output signal indicative of the presence of the constituent in a concentration above a predetermined level, a pulse generating circuit arranged automatically and periodically to activate the sensors for a selected relatively short interval during which detection but not poisoning can occur and subsequently to deactivate the sensors for a relatively long period, fault detecting circuits for producing a fault signal in the event of circuit failure or impending power failure, and alarm circuitry for providing a differentiated warning in response to the fault signal and in response to the output signal.