1,720,989 research outputs found
Planar thick-film pH electrodes based on ruthenium dioxide hydrate
No full textA planar thick film electrode for the potentiometric measurement of pH is introduced. The screen printed active layer is based on ruthenium dioxide hydrate held in a polymer matrix. The electrode has near-Nernstian (?59.15 mV/pH) behaviour in the pH range 2–10. As the electrode was aged over 60 days, the pH response was seen to be dependent on the conditions of storage. This behaviour is compared with that predicted by theoretical mechanisms for metal oxide pH response
An investigation of the factors influencing stability in continuously-powered screen-printed amperometric dissolved oxygen sensors
No full textThe continuously powered response of dissolved oxygen sensors fabricated as screen printed devices has been investigated. A reduction in the sensitivity of these devices has been observed when they are continuously powered at potentials of –0.6V versus Ag/AgCl reference electrodes. Periodically recorded voltammograms have indicated that the reduction in sensitivity can be attributed to a build up of hydroxyl ions beneath the sensor membrane that inhibits oxygen reduction. It has been found that powering these devices at more negative potentials mitigates against the decrease in sensitivity but results in a slowly increasing sensitivity. This is attributed to an increase in the effective area of the working electrode resulting mainly from leakage through the waterproofing layer covering the electrode interconnects
Screen-printed transcutaneous oxygen sensor employing polymer electrolytes
No full textA disposable, transcutaneous oxygen sensor has been designed and implemented using screen-printing technology for all fabrication stages. The sensor incorporates an integral heating element to promote transcutaneous diffusion of blood gases so that a reliable estimation of arterial blood gas concentration can be obtained. The oxygen sensing part of the device consists of a screen-printed Clark cell implemented as electrodes, electrolyte and membrane. A three-electrode configuration is employed with gold working and counter electrodes and a silver/silver chloride reference electrode. Several different polymer electrolyte and membrane materials were evaluated in the construction of the device, and their performances were compared. A fully automated gas testing rig was constructed to enable oxygen levels to be varied under computer control. Cyclic voltammetry and static analysis of the sensors were carried out at different oxygen concentration levels and in various test environments. Linear relationships were established with an averaged sensitivity level of 0.02 microA(mmHg)(-1) and high regression coefficients of 0.99. The prototype covered with a polytetrafluoroethylene membrane gave the experimental result of I (microA) = -0.025PO2 (mmHg) - 0.085. Several factors influenced the performance of the sensors. The investigations have greatly contributed towards an understanding of the suitability of the materials in achieving a viable, low-cost sensor
Transient and steady-state responses of thick-film oxygen sensors
No full textDisposable transcutaneous oxygen sensors have been designed and implemented employing screen-printing technology. The device is based on the working principle of amperometry and implemented with electrodes, electrolyte and an overlying membrane. A three-electrode configuration has been adopted with gold working and counter electrodes as well as a silver/silver chloride reference electrode. This paper focuses on the transient and steady state responses of the sensors obtained from a one-dimensional theoretical diffusion model, the results of which were compared to the experimental measurements. The surface contour and thickness of each layer was determined by analyzing the sensor using optical methods. The investigations have validated the effectiveness of using the theoretical model to perform preliminary response analysis. Furthermore, this method proves to be advantageous for the study of materials by reducing the development time and cost for future sensor designs
An evaluation of the characteristics of membrane materials suitable for the batch fabrication of dissolved oxygen sensors
No full textThe bulk batch fabrication process of thick film technology has been utilised in the design and production of miniature amperometric dissolved oxygen sensors based on potentiostatic and voltammetric operation. Three different polymers have been investigated as membrane materials – cellulose acetate, PTFE and PVC. PTFE has been deposited on the devices by aerosol spray and PVC and cellulose acetate by screen-printing. These methods have been shown to be effective membrane fabrication techniques, and have significant implications in the field of chemical sensors as a whole. All the membrane covered devices investigated were found to exhibit sensitive and linear responses to dissolved oxygen. The effects of temperature and flow rate on sensor response have been investigated and the use of PVC and PTFE in place of cellulose acetate have been shown to reduce both effects. These membranes have also been shown to reduce the detrimental effects of fouling observed on the surfaces of cellulose acetate covered devices as they are powered in tap water
Thermal conductivity of molten lead-free solders
No full textThe paper reports measurements of the thermal conductivity of a number of
molten solders for the electronics industry that are part of a group of materials
designed to be free of the toxic problems associated with lead-based
solders. The measurements have been carried out with a transient hot-wire
instrument originally designed for the measurement of the thermal conductivity
of pure molten metals. In the application reported here the instrument
has been used largely unchanged but an improved finite-element code has
been used for the analysis of the raw data so as to yield the thermal conductivity
of the molten solders. The measurements extend from the melting
point of the solder up to 625 K. The uncertainty in the thermal conductivity
measurements is estimated to be no larger than 3%
A novel low cost sensor for measuring cylinder pressure and improving performance of an internal combustion engine
No full textA new sensor has been developed which will enable engine pressure data to be available at a cost suitable for the average production vehicle. Unlike many previous devices this sensor will be suitable for the harsh environmental conditions of production vehicles themselves and not just the test environment. The sensor is small, extremely rugged and has a sufficiently wide bandwidth to be easily able to detect engine problems such as pre-ignition, miss-fire and malfunctioning engine components. Furthermore, the patented sensor technology does not require expensive electronic interfaces, but can use simple low-cost off the shelf components. The sensor's performance and limitations are discussed, based on real data from a single cylinder petrol engine. An analysis of the sensor output signals, showing both time and frequency domain data under varying load conditions, is also included
Repeatability and refinement of a transient hot wire instrument for measuring the thermal conductivity of high temperature melts
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