Pump-Sensor Devices

These devices are widely used for the control and monitoring of oxygen content in gas mixtures or liquid metals. Usually, the electrochemical pump and oxygen sensor are based on YSZ tubes with platinum electrodes. 

) are generally used. According to Faraday s law, the oxygen mole fraction 

The same device can be used for monitoring the composition of CO2-CO and Ar-H2O-H2 mixtures [76,77]. In that case, pure (H2, CO2) or premixed gases, such as Ar-5% H2 are used. According to Faraday s law, the equilibrium oxygen pressure versus the current intensity passing through the pump will obey the following equations  

The association of an electrochemical oxygen pump and an oxygen sensor allows 

The zirconia-based pump-sensor device can be used for controlling the oxygen partial pressure in closed systems typical applications include the oxygen permeation flux measurements, oxygen monitoring in molten metals, and coulometric titration. 

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The pump-sensor device described in section 21.1 can be used for the determination of the stoichiometry ratio in oxides using the device shown Fig. 9 a [Meas et al., 1978]. 

Fig. 9. (a) Experimental device for the study of gas-solid reaction imder constant oxygen pressure using a pump-sensor device, G vacuum gauge, LN liquid nitrogen trap (b) Variation of the stoichiometry ratio of Ce02-x at 1273 K. 

Of the various types of oxygen pumping sensors, the double-cell devices appear to have the best overall performance characteristics. These devices can be constructed to achieve the best combination of response time, independence of temperature and absolute pressure, insensitivity to electrode properties and operation not limited by the resistance of the Zr02 material. 

A second topology for vapor delivery to sensor devices entails preparing the desired air/vapor mixture in a flexible gas sample bag and then drawing the gas past the sensor head by a vacuum pump placed downstream of the sensor (Fig. 7.8). The air/vapor mixture is simply prepared by adding a... 

One significant advance in this area is the application of more and better electronic devices in the pump stations, such as improved frequency converters and computer programs which optimize the running costs of the pumps. Sensors can also be added to monitor the conditions inside the... 

Examples of analogous complete systems in chemistry are still rare. The best example is perhaps the artificial pancreas, in which a glucose sensor measures the actual blood-glucose concentrations in order to control an appropriate actuator, the insulin pump. Bedside devices for this purpose... 

Submersible and self-contained sensor devices to determine the numbers and sizes of individual particles directly in sea-water at various depths have been reported. 80-82 towed devices contained the necessary pumps... 

Pump-gauge devices are derived from amperometric and coulometric devices. They consist of a pumping part, to which a variable current can be applied, and a gauge part, which is used for measuring the resulting voltage. Only oxygen sensors are based on this principle. 

Oxide ion conductors have found widespread apphcations in our modem society. The devices based on oxide ion conductors include oxygen sensors, solid oxide fuel cells (SOFCs), and oxygen pump. 

The closed-loop system (often termed the artificial pancreas ) is essentially a more sophisticated version of the system described above. It consists not only of a pump and infusion device, but also of an integral glucose sensor and computer that analyses the blood glucose data obtained and adjusts the flow rate accordingly. The true potential of such systems remains to be assessed. 

Nearly all domestic appliances are using more and more electronics. Mechanical functions are replaced by electronic devices, mainly sensors and electromechanical actuators (such as pumps or electromotors) and microelectronic control systems. 

In parallel with improvements in chemical sensor performance, analytical science has also seen tremendous advances in the development of compact, portable analytical instruments. For example, lab-on-a-chip (LOAC) devices enable complex bench processes (sampling, reagent addition, temperature control, analysis of reaction products) to be incorporated into a compact, device format that can provide reliable analytical information within a controlled internal environment. LOAC devices typically incorporate pumps, valves, micromachined flow manifolds, reagents, sampling system, electronics and data processing, and communications. Clearly, they are much more complex than the simple chemo-sensor described above. In fact, chemosensors can be incorporated into LOAC devices as a selective sensor, which enables the sensor to be contained within the protective internal environment. Figure 5... 

Integrating liquid-liquid extraction and detection is far from easy, as reflected in the few attempts made so far. Many of the devices developed for this purpose fail to comply with the definition of sensor. Such is the case with continuous liquid-liquid extraction systems without phase separation, where programmed switching of the propulsion system (a peristaltic pump) allows the extracting phase to be passed iteratively by the detection point in a back-and-forth motion that enriches it gradually with the extracted species [9-11]. This type of system is much too Complex to be considered a sensor, though in addition, the extraction process is not completely simultaneous with detection. 

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