Low-temperature sensors

The limit for the operating temperature of CMOS-microhotplates can be extended by using the microhotplate that was presented in Sect. 4.3. We now detail high-temperature microhotplates with Pt-resistors that have been realized as a single-chip device with integrated circuitry. While the aluminum-based devices presented in Sect. 4.1 were limited to 350 °C, these improved microhotplates can be heated to temperatures up to 500 °C. As the typical resistance value of the Pt-resistor is between 50 and 100 Q, a chip architecture adapted to the low temperature sensor resistance was developed. The system performance was assessed, and chemical measurements have been performed that demonstrate the full functionality of the chip. 

Develop a low temperature sensor for measuring 10-100 ppm range concentrations for stack poisoning control. 

We have successfully developed low temperature sensors for the monitoring of carbon monoxide gas in a hydrogen stream. The sensors can detect parts per million concentrations of carbon monoxide in either a pure hydrogen or a hydrogen/carbon-dioxide... 

Specific low-temperature sensors biosensors optical sensors fabrication hotplate platforms... 

Low-temperature sensors surface plasmon resonance sensors pellistors biosensors High-temperature electrochemical gas sensors sensors for tough conditions electronic nose RT electrochemical sensors Membranes filters for aU types of sensors SAW sensors cantilever-based sensors... 

Low-temperature sensors SAW sensors biosensors humidity sensors conductometric gas sensors membranes electrochemical sensors cantilever-based sensors optical and fiber-optic sensors electronic noise... 

Recently, Liaw and Weppner have proposed tetragonal zirconia for measiuements down to 250°C. BijOj-ErjOj solid solutions are also good candidates for low-temperature sensors. Amperometric oxygen sensors based on PbSnF4 already operate at room temperature. ... 

Fig. 19. (a) Low level sensor. In the absence of media, the heated sensor tip causes a temperature differential between the two sensors, (b) High level sensor. As media contacts the sensing assembly, heat is dissipated and temperature differential decreases. 

Improved sensors allow computer monitoring of the system for safety and protection of the equipment from damage. Sensors include lubrication-flow monitors and alarms, bearing-temperature sensors, belt scales, rotation sensors, and proximity sensors to detect ore level under the crusher. The latter prevent jamming of the output with too high an ore level, and protect the conveyor from impact of lumps with too low an ore level. Motion detectors assure that the conveyor is moving. Control applied to crusher systems including conveyors can facilitate use of mobile crushers in quarries and mines, since these can be controlled remotely by computer with reduced labor. 

Low temperature sol-gel technology is promising approach for preparation of modified with organic molecules silica (SG) thin films. Such films are perspective as sensitive elements of optical sensors. Incorporation of polyelectrolytes into SG sol gives the possibility to obtain composite films with ion-exchange properties. The addition of non-ionic surfactants as template agents into SG sol results formation of ordered mechanically stable materials with tunable pore size. 

A thermistor is a thermally sensitive, semiconductor solid-state device, which can only sense and not monitor (cannot read) the temperature of a sensitive part of equipment where it is located. It can operate precisely and consistently at the preset value. The response time is low and is of the order of 5-10 seconds. Since it is only a temperature sensor, it does not indicate the temperature of the windings or where it is located but only its preset condition. 

Mosadegh Sedghi S, Mortazavi Y, Khodadadi A (2009) Low temperature CO and CH4 dual selective gas sensor using Sn02 quantum dots prepared by sonochemical method. Sens Actu B (In Press)... 

Molecular rotors are fluorophores characteristic for having a fluorescent quantum yield that strongly depends on the viscosity of the solvent [50], This property relies on the ability to resume a twisted conformation in the excited state (twisted intramolecular charge transfer or TICT state) that has a lower energy than the planar conformation. The de-excitation from the twisted conformation happens via a non-radiative pathway. Since the formation of the TICT state is favored in viscous solvents or at low temperature, the probability of fluorescence emission is reduced under those conditions [51]. Molecular rotors have been used as viscosity and flow sensors for biological applications [52], Modifications on their structure have introduced new reactivity that might increase the diversity of their use in the future [53] (see Fig. 6.7). 

The sol-gel process allows the preparation of glass films into which indicator chemistry can be incorporated. The production of ceramic materials and glassy networks is based on the polymerisation of suitable precursors at low temperature. The increasing popularity of sol-gels in sensor applications results from the processing versatility2. 

The major requirement for a reliable hydrogen sensor operation in the fuel cell environment is in 100% condensing humidity Most of the fuel cells have abundant humidity and the sensor needs to operate continuously in humid environments. In some cases, the hydrogen sensor can also be operated at very low temperatures (as low as —40°C). The fuel cells regularly have a cold start, when operated from a very low ambient temperature the sensor needs to attain ambient temperature quickly (<30 s) and continue operation well below ambient temperature before the fuel cell itself reaches the ambient temperature. 

The resistance thermometry is based on the temperature dependence of the electric resistance of metals, semiconductors and other resistive materials. This is the most diffused type of low-temperature thermometry sensors are usually commercial low-cost components. At very low temperatures, however, several drawbacks take place such as the low thermal conductivity in the bulk of the resistance and at the contact surface, the heating due to RF pick up and overheating (see Section 9.6.3)... 

T. Junquera et al. Neutron Irradiation Tests of Calibrated Cryogenic Sensors on Low Temperatures, CERN-LHC Project Report n°153 (1997)... 

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