Temperature electric current sensors

The hot-wire anemometer sensor is a very fine wire with a diameter of few micrometers and length of few millimeters. This wire is connected to a measurement bridge and an electrical current is fed through the wire. The wire is heated to a temperature above the air temperature and the air velocity is determined by the cooling effect of the wire. The voltage over the wire, U, is a function not only of the velocity but also of the excess temperature and the fluid properties in the following way ... 

The other limit is the problem of temperature measurements. Classical temperature sensors could be avoided in relation to power level. Hence, temperature measurements will be distorted by strong electric currents induced inside the metallic wires insuring connection of temperature sensor. The technological solution is the optical fiber thermometers [35-39]. However, measurements are limited below 250 °C. For higher values, surface temperature can be estimated by infrared camera or pyrometer [38, 40], However, due to volumic character of microwave heating, surface temperatures are often inferior to core temperatures. 

Muscles contract and expand in response to electrical, thermal, and chemical stimuli. Certain polymers, such as synthetic polypeptides, are known to change shape on application of electric current, temperature, and chemical environment. For instance, selected bioelastic smart materials expand in salt solutions and may be used in desalination efforts and as salt concentration sensors. Polypeptides and other polymeric materials are being studied in tissue reconstruction, as adhesive barriers to prevent adhesion growth between surgically operated tissues, and in controlled drug release, where the material is designed to behave in a predetermined matter according to a specific chemical environment. 

In this chapter, the development of an amperometric sensor will be explained and discussed. The principle of the analysis method will be based on the results described in Chapter4 this means that use will be made of the oxidation reaction of hydrogen peroxide in the prewave, and that the concentration will be determined using the rate equation. In addition to measurement of the electrical current response, temperature and pH will therefore also be measured. Accordingly, it is interesting to start with an investigation of the temperature influence. 

The definition of a sensor is that it reacts to a parameter (for example, the volume of the mercury pool in a thermometer increases with temperature), and the intensity of the reaction is in relation to the parameter - for example, the measurement of an electrical current that is in relation to the concentration of the analyte oxidised or reduced at the electrode surface. The parameter to be investigated is the concentration of the analyte, while the parameter measured is an electrical current. As for the real devices, ultimately most signals are being transformed into electric ones. Electroactive materials are consequently of utmost importance with respect to intelligent textiles. Of course, apart from technical considerations, concepts, materials, structures and treatments must focus on the appropriateness for use in or... 

In a smart building, computers and sensors would measure light striking windows and the room temperature and adjust the electrical current to the electrochromatic windows. Huge energy savings are envisioned because ot reduced demand lor electricity to run air conditioners or for heating fuels. 

Due to their compactness and standard fabrication technology, the temperature in thermal flow sensors is often measured by thermocouples, which rely on the thermoelectric effect. The thermoelectric effect describes the coupling between the electrical and thermal currents, especially the occurrence of an electrical voltage due to a temperature difference between two material contacts, known as the Seebeck effect. In reverse, an electrical current can produce a heat flux or a cooling of a material contact, known as the Peltier effect. A third effect, the Thomson effect, is also connected with thermoelectricity, where an electric current flowing in a temperature gradient can absorb or release heat from or to the ambient [10, 11]. The relation between the first two effects can be described by methods of irreversible thermodynamics and the linear transport theory of Onsager in vector form. 

When an electrical current /q is applied on a thermoresistive flow sensor and its self-Joule heating is maintained at a constant level, any fluid flow through the sensor will cause a shift in its temperature and thus resistance R, respectively. As a result, a decrease in the voltage V (=1qR) of the sensor will be detected. The aim of the thermoresistive flow sensor is to evaluate such changes caused by variations of the flow rate alone. 

Input electric current is introduced to the heater through certain pads to generate heat. Another option is through pads that have compensation resistors whose characteristics resemble those of the heater. Figure 5 shows the sensor s typical output. It describes the thermopiles output voltage difference as a function of gas flow velocity. This output is a result of an experiment where nitrogen gas flow in the range of 0-1,000 standard cubic centimeters per minute at room temperature was introduced. 

Lai et al. (1997) fabricated a chip calorimeter with a 100 nm thick Si-N membrane with two Ni thin-film stripes (30 nm thick and 0.4 mm wide) as the differential heater pair, one serves as the sample heater and the other as the reference heater. With two synchronized electrical current pulses, the two heaters can be heated up to 300 °C at a rate of about 30000Ks. The heater stripes also function as temperature sensors. The apparent heat capacity of the chip is about 6 x 10 J at 300 K and the lowest detectable heat is given as 0.2 nj. 

Hot-wire anemometers ( micro/nano anemometers) have been developed for a wide spectrum of applications from experimental fluid mechanics to aerospace engineering to measure physical parameters such as temperature, flow rates, and shear stress. The advent of microelectromechan-ical systems (MEMS) and nanoscale thermal sensors has provided an entry point to microfluidics, biomedical sciences, and micro-circulation in cardiovascular medicine. These MEMS and nanoscale devices are fabricated with semiconductor-based sensing elements which harbor the physical property of a resistor and have the dimension of one-tenth of a strand of hair. On the basis of the heat transfer principle, these resistant elements are heated by the Joule effect due to the passage of electric current. As the... 

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