Instrumentation, near sensors

The instrument should be placed away from other instrumentation and the propeller axis carefully aligned to be vertical. The specifications of this sensor are the same as those of the wind sensor. Because this instrument will frequently be operating near its lower threshold and because the elevation angle of the wind vector is small, such that the propeller will be operating at yaw angles where it has least accuracy, this method of measuring vertical velocity is not likely to be as accurate as the measurement of horizontal fluctuation. 

Fig. 3.21 Example of temperature variation as measured by MIMOS II temperature sensors on MER (i) inside the rover body at MIMOS electronics board (black curve), (ii) outside the rover, at the MIMOS II SH (green and red curves), which is at ambient Martian temperature (a) inside the sensor-head, at the reference absorber position (green), (b) outside the SH at the sample s contact plate (red). Temperatures at the two SH positions are nearly identical (difference less than 2 K). During data transmission between the rover and the Earth (or the relay satellite in Mars orbit) the instrument is switched off resulting in immediate small but noticeable temperature changes (see figure above)...

Figure 7.9. Schematic diagram of a surface plasmon resonance biosensor. One of the binding partners is immobilized on the sensor surface. With the BIACORE instrument, the soluble molecule is allowed to flow over the immobilized molecule. Binding of the soluble molecule results in a change in the refractive index of the solvent near the surface of the sensor chip. The magnitude of the shift in refractive index is related quantitatively to the amount of the soluble molecule that is bound.

The majority of currently deployed IR sensors operate in the near-IR. Although near-IR sensors suffer from limited selectivity and sensitivity due to the relatively unstructured broadband absorptions in this frequency range, the easy availability of waveguides and other instrumentation give this spectral range a significant advantage over the mid-IR. Main application areas involve substance identification and process control. 

Similar to IR sensors, process analysis is the prevalent application area. Due to the applicability of standard VIS instrumentation, Raman probes have been used for more than two decades65, 66. Typically, Raman probes are applied where near-IR probes fail and hence are in direct competition to mid-IR probes. 

In this section we will review the application of near-IR system instrumentation to the most commonly encountered fluorescence measurements such as steady-state spectra, excited state lifetimes, anisotropy, microscopy, multiplexing, high-performance liquid chromatography (HPLC), and sensors. 

A fast chemical sensor that operates at a reduced pressure of 50 torr (6700 Pa) and with a flow of 1 standard liter per minute must be maintained in an instrument shelter. Considerations of flow distortion require that 10 m separate the sensor from its intake on the tower near the sonic anemometer. Three ducting arrangements can be considered. The first would involve drawing air along 10 m of 1/4-inch tubing (0.2 cm internal radius) and controlling the flow and pressure at the sensor itself. The second option would place the pressure-flow controller at the inlet and allow the inlet intake to flow at the reduced pressure. The third course would be to use a... 

Studies of atmospheric properties using IR spectroscopy techniques have been reported in the literature for nearly 100 years. This paper presents a brief historical review of the development of this area of science and discusses the common features of spectrographic instruments. Two state of the art instruments on opposite ends of the measurement spectrum are described. The first is a fast response iri situ sensor for the measurement of the exchange of CO2 between the atmosphere and the earth s surface. The second is a rocketborne field-widened spectrometer for upper atmosphere composition studies. The thesis is presented that most improvements in current measurement systems are due to painstakingly small performance enhancements of well understood system components. The source, optical and thermal control components that allow these sensors to expand the state of the art are detailed. Examples of their application to remote canopy photosynthesis measurement and upper atmosphere emission studies are presented. 

Progress in the application of sensor arrays to gas analysis will be made through increasingly independent data channels using novel combinations of sensors and operating modes. Computational approaches will be modified to suit specific types of sensor arrays and to make economical use of computational space for portable instrument applications. The primary challenges of the near future will be to solve the "needle-in-the-haystack" problem and to proceed to complex mixture analysis using a plurality of sensor responses. 

Field Devices Hardware devices typically located in the field at or near the process, necessary for bringing information to the computer or implementing a computer-driven control action. Devices include sensors, analytical instruments, transducers, and valves. 

Overall, the prospects for development of practical electronic noses based on AW sensor arrays and computerized pattern recognition are very good. A current design for such an instrument consists of an array of four 250-MHz SAW resonators along with RF electronics, frequency counters, interface circuitry, and neural-network pattern-recognition computer. The complete instrument occupies a volume of 500 cm (i.e., 11.4 X 11.4 X 3.8 cm) and uses less than 2 W of power. Improvements in the near future should allow the volume to shrink to less than 160 cm with a power consumption of about 0.7 W. While this is still a rather large nose, further improvements in size and performance are quite likely. Thus, the quest for a small instrument having a volume of a few cubic centimeters and the ability to detect and identify vapors at the part-per-million concentration level (i.e., a truly versatile electronic nose) appears to be achievable. 

To some extent, progress has been limited by the availability of measurements on exchange processes. Until recently, temperature microstructure measurements were the primary approach to quantify near-surface turbulence. The instruments needed to do this were expensive and difficult to operate. The situation is now considerably improved. Microstructure sensors more suited to field use are commercially available, and are more user-friendly . Alternative methods to observe or infer mixing processes have also been perfected, including free-fall CTDs, acoustic doppler sensors and acoustically monitored floats. As these techniques are refined and deployment, operation, and analysis become more routine, it will become increasingly practical to incorporate a mixing component into field studies of UVR effects. 

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