Conductivity sensor

It has been proposed to use a Si/Si02/electrolyte structure for the detection of immunochemical reaction. The antibodies are immobilized at the surface of the Si02 and their interaction with the antigen is monitored by observing the shift of the inflex point on the C-V curve, using 150 mV p-p, 1 KHz modulation. 

Suggest an equivalent circuit diagram corresponding to this experiment and explain what causes the shift of the inflex point. 

Therefore, both basic and acidic analytes can be successfully detected by PANi films and nanofibers. This was illustrated by the PANi-PEO blend nanofiber (or nanowire) device described by Liu et al. (2004). Nanofibers made by scanned-tip electrospinning of a droplet of the blend solution were deposited across a pair of gold electrodes. The spinning solution of the polymer blend was doped with 10-camphosulfonic acid (CSA). The resulting nanowire detector of protonated PANi nanofibers reacts with NH3, changing its electrical resistance (Fig. 8.6) and displayed a threshold detection of 0.5 ppm of NH3. In the figure, normalized resistance [(R/Ro) — 1] is plotted as a function of the analyte concentration. 

Virji and colleagues reported the use of PANi nanofibers for detection of acids as well as NH3 (Viiji et al. 2004). In both instances the nanofiber 

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Conductivity sensors are most commonly used for safety purposes in household appliances. Presence and absence of washing liquor, detergency, and water softener can be easily measured and proper operation ensured [71]. The various applications mainly differ by their design of electrode geometry and methods for electrical measurement. Due to the close relation between ionic conductivity and water hardness, the automatic water softener in an automatic dishwasher can be controlled by a conductivity sensor [72]. To isolate the transmission of the measured value from the process controller, the conductivity sensor could incorporate an opto-electronical coupling [73]. Thus, protective insulation of the electrodes in a washer-dryer could be ensured. 

The sensor head is lowered into a monitoring well. Upon contact with any fluid, the float ball is raised and a continuous tone emitted from an audible alarm. When the sensor head contacts the interface between LNAPL and groundwater, the change in conductive properties is detected by the electrical conductivity sensor and a beeping tone is emitted. The distances along the tape at which the two changes in the audible alarm occur are recorded as referenced from a presurveyed point on the lip of the monitoring well. The resultant distance is equivalent to the apparent thickness of the LNAPL in the well. 

I. Simon and M. Arndt. Thermal and gas-sensingproperties of a micromachined thermal conductivity sensor for the detection of hydrogen in automotive applications . Sensors and Actuators A97-98 (2002), 104-108. 

Figure 4 shows a test of the diagnostic system for an incident of resin exhaustion for a cation conductivity sensor. The data are a combination of real and synthesized plant data and are given in Table IV. The condensate values for the condensate sensor are those recorded during the actual exhaustion of the... 

Infrared photometers Paramagnetic oxygen sensors Thermal conductivity sensors Distillation-type analyzers 1 930s and 1 940s Refining... 

When the system which was to be linked to the autosampler system was purchased, it was found that the conductivity cell was excessively large and primarily designed to be fitted to a A" pipehne for analytical purposes this was clearly too large. However, the pH cell provided an Ingold standard electrode system with dimensions which allowed it to be placed within the conductivity sensor, as shown in Fig. 7.21. It is therefore possible to configure a flow cell in which the conductivity sensor houses the pH electrode. The latter also serves to take up most of the cell volume so that the wash-out requirements are not too excessive. The cell is filled by taking a sample from the autosampler with pump 1 hquid fills the cell and overflows via the weir arrangement and the top of the cell. 

The isopiestic and manometric methods (units A2j A2.4) for determination of water activity have the limitation of being dependent on fixed laboratory equipment. The electronic-type sensors have advantages of portability, speed, and simplicity of measurement. The characteristics of a sensor depend upon the manufacturer and each instrument must be calibrated separately. The anodized sensors have advantages of ruggedness, small dimensions, and fast response, as well as freedom from large temperature coefficients and less susceptibility to contamination of the lithium chloride conductivity sensors (Smith, 1971). 

A typical arrangement for an on-line process refractometer is shown in Fig. 6.45. Besides the prism, which is in contact with the process liquid, there is commonly a light source, a beam collimator and a photo-conductive sensor. As the nature or concentration of the process liquid varies, the critical angle changes, so moving the internally reflected collimated beam of light across the photo-detector. The latter is divided into two sections, one of which is arranged to receive a constant amount of... 

Flow-through conductivity sensors suitable for insertion in pipelines (see Fig. 6.47a) are now available for use at temperatures up to 480 K. and pressures up to 1700 kN/m2(64). As conductivity is temperature sensitive, a thermistor is usually included in the detector circuit as part of a temperature compensator. Screw-in cells (Fig. 6.476) will withstand higher pressures. More recently, electrodeless methods of measuring conductivity have become available. In this case the solution is placed between two energised toroids. The output voltage of the instrument (from the output toroid circuit) is proportional to the conductivity of the solution provided that the input voltage remains constant. This type of conductivity meter can be used under much more severe conditions, e.g. with highly corrosive or dirty systems 43 . 

Gas thermal conductivity sensors are used to detect variations in the composition of mixtures of gases by monitoring changes in the thermal conductivity of the mixture. Such instruments are used (a) as detectors for gas chromatographs (Section... 

Tracer methods, both visual and electrical conductivity sensors, have been applied to measure the residence time of the liquid in the rotor (15,26). Measured liquid residence time ranges from about 0.2 seconds to about 1.8 seconds. Time decreases as the rotor speed increases, as liquid flow rate increases, and as the radial position increases. Gas flow rate and liquid viscosity (narrow test range) have little impact on residence time (15,19,26). 

Schlautmann, S., Wensink, H., Schasfoort, R., Elwenspoek, M., van den Berg, A., Powder-blasting technology as an alternative tool for microfabrication of capillary electrophoresis chips with integrated conductivity sensors. J. Micromech. Microeng. 2001, 11, 386-389. 

SrTi03 may serve as a well-investigated material for such a bulk conductivity sensor. Its defect thermodynamics and also the relevant kinetic parameters have been discussed in detail in Part I.2 In particular at low temperatures and at small sample thicknesses L, the kinetics of oxygen incorporation becomes surface reaction controlled, and ks the decisive kinetic parameter. 

Important advantages of the bulk conductivity sensor are, besides selectivity, its simplicity (no reference needed) and its selectivity an important drawback is the T-dependence which can be quite significant (see above). Improvement via doping or by using a T-reference is straightforward, but partly at the cost of sensitivity, simplicity, or range of application. 

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