Sensor electrical

The vane anemometer is an old invention. It can be likened to a small wind turbine with 4-10 rotating blades and a handle, as in Fig. 12.20. Earlier constructions were fully mechanical, where the spindle rotation was transmitted to a pointer through a series of gears. In modern vane anemometers, an electrical sensor records the spindle rotation and the signal is processed, giving the velocity on a digital display. Such an instrument usually is able to integrate the mean velocity over a time interval. 

The working of a chemical sensor is based on the interaction between free particles (e g. gas molecules) and the surface of a solid. This interaction might be a physical absorption and in that case the sensor can be used at low temperatures because the absorption forces will not be great. However, the absorption might also be chemical and then there is question of a strong chemical bond to the surface of the sensor. This can lead to very specific changes in the electrical sensor properties. 

Electrical sensors offer many benefits due to their versatility and ease of use. Another important factor relates to the ease by which an electrical event may be monitored, using simpler and therefore less expensive approaches than those required for following an optical event. Much of this work on electronic sensors has been previously reviewed [11]. 

Fig. 13-2. Scheme for measuring Hg content of soil using thermo-emission method 1 = temperature control, 2 = thermo-electric sensor, 3 = sample, 4 = furnace, 5 = Na2C03 filter, 6 = Au wire amalgamation trap, 7 = vacuum pump, 8 = Hg detector. 

Electrical sensors are based on measurements where no electrochemical processes take place, but the signal arises from a change of electrical properties caused by the interaction of the analyte. 

Archer M, Christophersen M, Fauchet PM (2004) Macroporous silicon electrical sensor for DNA hybridization detection. Biomed Microdevices 6 203-211... 

The basic equipment of a weather station is comprised of a facility referred to as Meteorological Automatic Weather Station (MAWS). A MAWS is equipped with electric sensors a PtlOO resistance sensor for temperature, a... 

Hydrological monitoring is based on data collected from 1000 gauging stations in rivers, lakes and water reservoirs. Information on the water levels is supplied in 10 minute cycles. Water level gauges used by hydrological stations are either electric sensors for hydrostatic pressure or optical sensors. The hydrological monitoring system is of key importance for flood risk evaluation and for prevention of flood effects. 

Figure 6.29. (a) A photograph of an autoclave custom-modified to enable the accommodation of optical and electrical sensor systems for cure monitoring of advanced reinforced composites via contact and non-contact IR spectroscopy and measurements of residual strain and temperature. 

A smoke detector is a device that sounds an alarm in the presence of smoke particles from a smoldering or burning object. An ionizing smoke detector, like the one illustrated here, contains an electrical sensor that detects smoke particles that interrupt an electrical current. Ionizing detectors usually contain the unstable isotope americium-241 ( IgAm), which decays to form 93 Np and fHe. 

Parameters previously described in Chapters 3 to 5 are related to either specific compounds or groups of compounds, always in solution. Other parameters must be considered to complete the physico-chemical characterisation of water and wastewater. These parameters can be quantified either by electrical sensors (or similar) such as temperature, redox potential or conductivity (which is actually related to the sum of conducting species), or by optical methods for the determination of colour, turbidity or suspended solids. The latter parameters using UV-visible light are presented in this chapter. 

Important electrical properties of porous SiC are discussed in Chapter 9. Not surprisingly, porous SiC has a higher specific resistivity than its host crystals. More significantly, pores appear to trap charge carriers, which renders p-SiC semi-insulating. Such effects strongly influence the use of porous material as electrical sensors. 

A schematic representation of the most advanced set-up, based on the latest scientific findings, the MPTl from LAUDA, is shown in Fig. 5.12. The air coming from a micro-compressor flows first through the flow capillary. The air flow rate is determined by measuring the pressure difference at both ends of the flow capillary with the electric transducer PSl. Thereafter the air enters the measuring cell. The excess air pressure in the system is measured by a second electric sensor PS2. In the tube which leads the air to the measuring cell, a sensitive microphone is placed. 

Sensing techniques that are applicable to the measurement of solids concentration can be classified into four groups electrical, attenuation, resonance, and tomographic. The electrical methods utilize the dielectric and electrostatic properties of solids. Typical electrical sensors are capacitive and electrodynamic sensors the capacitive sensors measure the dielectric property of the solids, whereas the electrodynamic sensors detect the static charges that develop because of collisions between particles, impacts between particles and pipe wall, and friction between particles and gas stream. Attenuation methods are used with optical, acoustic, and radiometric sensors. Both optical and acoustic sensors are applicable to relatively low concentrations of solids. Radiometric sensors, in which y-rays or X-rays are used, are expensive and may raise safety concerns. They can, however, offer accurate and absolute measurement of particle velocity and thus can be used as calibration tools for other low-cost sensors such as the capacitive sensor. Resonance and tomographic methods, which are still in developmental stages, will be briefly introduced in Section 6.5. 

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