Sensors internal resistance

H. Breunig, F. Lieneweg. Handbucb der technischen Temperaturmessung. Vieweg, 1976. lEC 60751 (1983-01). Industrial Platinum Resistance Thermometer Sensors. International Electrotechnical Commission, 1983. 

Electrochemical cells are of two types power cells and sensors. In an ideal power cell, the ionic current through the electrolyte inside the cell matches an electronic current through an external load. The solid electrolyte is in the form of a membrane of thickness L and area A that separates electronically the two electrodes of the cell. Any internal electronic current across the electrolyte reduces the power output. The internal resistance to the ionic current is... 

Atahigh temperature (r>400°C), the dielectric sensor behaves as apure resistive circuit because of the decrease of the internal resistance of the capacitors, that is, Rx and R, (see Figure 4.41). In this instance, the following approximation obtained from Equation 4.33 is valid [15] ... 

Because the 02 signal is derived from the interaction of pumping and Nernst cells, this sensor requires a special electronic controller circuit. This ASIC (application-specific integrated circuit) includes the basic pumping current control, internal resistance measurement, and extended hardware diagnostics for the sensor. 

Figure 7.14 shows photographs of two DTEGs with Sn02 as the gas sensitive films. The sensors were manufactured as shown in Fig. 7.2. The gas sensitive layer was applied with a brush to ensure low internal resistance of the gas sensitive layer (due to the geometry independency of the measurand thermopower, the geometry does not play a role ). The sensors also had a heater on the reverse side. It heated the entire sensor tip to the operational temperature of 400°C. The temperature modulation was applied by the modulation heater with a modulation frequency of 0.312 Hz. A continuous regression was used to extract the thermopower of the gas sensitive layer.

It was shown in this section that it is possible to manufacture accurate, rapid and sensitive DTEGs.The design of the direct thermoelectric gas sensors can be developed knowledge-based. Since intrinsic materials show the best sensitivity, the internal resistance of the gas sensitive layers has to be considered, and the insulation and equipotential layers have to be applied. An appropriate temperature modulation frequency needs to be selected to achieve good results. 

In this electronic age, it is mandatory to use solid polymer electrolytes for different applications in science and technology. Polymer electrolytes can be shaped in the form of thin film, thereby reducing the internal resistance leading to application as gas sensing material. Few reports appeared on proton-conducting polymer films and their application to gas sensors [65]. 

Grain internal resistance (Ri) of zirconia particle on the real axis as lead wires and solid electrolyte, zirconia grain boundary matrix resistance (R2), and interface resistance (R3) between zirconia Pt electrodes constitute DC component. The sensor element is exposed to the exhaust gas and R3 resistance suffers effect of the atmosphere. Therefore, if resistance component of the mainstream of grain internal resistance is realized, the sensor element resistance to detect in the high-frequency region, relationship between the sensor element temperature and resistance can be realized without effect of the atmosphere. 

Finally, if we heat the sensor-substrate with deposited silver atoms using internal heater (platinum film attached to the back side of the sensor-substrate) up to 700 C then the surface of zinc oxide gets completely cleaned of silver. This can be confirmed by the value of resistivity of sensor-substrate which comes back to the initial value of 2.1 MOhm (the silver during such treatment partially evaporates, partially migrates to the contacts). The experiment showed that as a result... 

Here R0 is the resistance at 0°C, and a and b are coefficients whose values are specified in internationally agreed standards covering platinum temperature sensors, for example DIN EN 60751. The coefficient b is so small that for most applications one can assume a linear relation between Rt and the temperature t. 

RTDs are constructed of a resistive material with leads attached and placed into a protective sheath. Platinum resistance thermometers are the international standard for temperature measurements between the triple point of H2 at 13.81 K (24.86°R) and the freezing point of antimony at 630.75°C (1,167.35°F). The RTD elements include platinum, nickel of various purities, 70% nickel/30% iron (Balco), and copper, listed in order of decreasing temperature range. Their features and relative performance characteristics in comparison with other sensors are tabulated in Table 3.169. 

Since we are attempting to reconcile measurements made by different techniques, the artifacts, limits and constraints that accompany each technique must be identified. These include the challenges inherent in the methods of sample-sensor coupling. For example, fhermal femperafure or heat flow sensors are influenced by factors such as the thermal conductivity of the cell-sensor construct, the thermal resistance of fhe sample-cell interface, and the internal thermal properties of the sample. The geometry of the heat flow pathways is also important. Mechanical sensors (force or... 

Usually in the operation of biosensors the flow conditions are adjusted to provide a mass transfer rate from the solution to the membrane system which is fast as compared with the internal mass transfer (exception implanted sensors). On the other hand, variations of the diffusion resistance of the semipermeable membrane are being used to optimize the sensor performance. A semipermeable membrane with a molecular cutoff of 10 000 and a thickness of 10 pm only slightly influences the response time and sensitivity. In contrast, thicker membranes, e.g. of polyurethane or charged material, significantly enhance the measuring time, but may also lead to an extension of the linear measuring range. 

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