Vapor pressure sensors

Our automotive pressure sensor line offers a wide range of choices. At one end of the range is the gasoline vapor pressure sensor for 5 kPa used to detect leaks from the gasoline pipe. At the other end is the common-rail pressure sensor for... 

To improve the fuel vapor-pressure sensor accuracy, we reduced the mechanical strain conveyed from the package to the sensor device. Fig. 7.3.14 shows the structure of the fuel vapor-pressure sensor for 5 kPa. We chose a relatively thin silicon diaphragm, 14 pm, to achieve the sensitivity required for 5 kPa detection. That makes the sensor device more susceptible to the mechanical strain conveyed from the resin package. To solve that problem, we analyzed the effect of the mechanical strain from the package by FEM. 

If basic calculations such as those presented are to be conducted, it is important to collect enough weather parameters to calculate reference evapotranspiration ETf). An on-site weather station should be considered a basic requirement minimum sensor requirements to calculate a Penman equation would include solar radiation, wind speed, relative humidity or actual vapor pressure, and air temperature. An on-site rain gauge is essential but it is also a good idea to have a rain gauge on the weather station even if it is not directly on-site. The most accurate variations of the Penman equation calculate Tq on an hourly basis. However, Penman routines using daily summaries are typically satisfactory for the purpose of calculating soil-water recharge. 

Fig.4.8. Oscilloscope traces of variation of the electric conductivity of a ZnO sensor upon admission of isopropyl alcohol vapor to the vessel (the initial vapor pressure is 0.01 Torr) at the temperature of 390 C (/), 370 C (2), 350 C (5), 320 C (4), and upon admission of H2 at the temperature of 390 C (5).

An optional high-pressure crucible (Fig. 8 1) may be used for chemical reactions in solutions with an inherent vapor pressure of up to 100 atmospheres. The crucible is equipped with a centering pin for exact positioning on the measuring sensor. 

The explosives mentioned here are only a few selected from a long list of materials that can be used as explosives. This presents an unusual detection challenge. The chemical and physical properties of explosives vary widely, so it is a challenge to design a sensor that can detect all explosives equally well. One such property is the equilibrium vapor pressure of explosives. From Figure 7.1, which is a plot of the equilibrium vapor pressures of selected explosives at 25°C,... 

Selective, highly sensitive sensors that can detect trace amounts of explosive vapors in real time are needed to help combat terrorism [1-4], Trace detection of explosives, however, is a formidable task. Selectivity is difficult to achieve because many chemicals can be used as explosives, and they differ from each other in their chemical properties. The extremely small vapor pressures of the explosives make it challenging to achieve highly sensitive vapor-based detection. Also, because the terrorist threat is very broad, combating it requires widespread deployment of inexpensive, low-power-consuming sensors. Therefore, devices... 

The principle of the saturated sail dew point sensor is based on the relationship that the vapor pressure of water is reduced in the presence of a salt. When water vapor in the air condenses on a soluble salt, it forms a saturated layer on the surface of the salt. This saturated layer has a lower... 

Limitations of saturaled sail sensors include (11 relatively slow response lime and (2) a lower limit to the mcasurcmenl range imposed by ihe nature of lithium chloride. The sensor cannot be used to measure dew points when the vapor pressure of waier is below- the saturation vapor pressure of lithium chloride, which occurs at about I 1% RH. In certain gases, ambient temperatures can he reduced, increasing the RH to above I 1% but the extra effort needed to cool the gas usually warrants selection of a different type of sensor. Fortunately, a large number of scienlilie and induslrial measurements fall above this limitation and are readily handled by the sensor. 

Aluminum Oxide Moisture Sensor. This type of sensor is a capacitor, formed by depositing a layer of porous aluminum oxide onto a conductive substrate, and then coaling the oxide with a thin film of gold The conductive base and the gold layer become the capacitor s electrodes. Water vapor penetrates the gold layer and is absorbed by the porous oxidation layer The number of water molecules absorbed determines the electrical impedance of the capacity, which is. m turn, a measure of water vapor pressure. 

A2.1 Factors to Consider When Estimating Water Vapor Pressure A2.2 Dew-Point Method for the Determination of Water Activity A2.3 Measurement of Water Activity Using Isopiestic Method A2.4 Direct Manometric Determination of Vapor Pressure A2.5 Measurement of Water Activity by Electronic Sensors... 

Figure A2.1.1 A representation of a vapor-pressure-evaluating system. Region A includes the sample and its environment. Region B is a vapor transfer path to the sensor region, C, which includes the sensor and its environment. TA and Tc are the temperatures in regions A and C, respectively.

The sensitivity of the sample or the sensor to vapor transfer must also be considered. Here, the quantity of material represented by the sample or by the sensor is important. Vapor pressure is established by the presence of a particular number of molecules in a defined volume of space. The transfer of water molecules into the vapor phase may cause a measurable change in the gravimetric water contents of the sample and sensor. It is necessary that the sample water content (or the initial sample weight) be known. It may also be necessary to... 

Unless the temperature of the sample is known, the relative humidity in the sample region is unknown. Unless the sensor temperature is known, the relative humidity indicated by the sensor cannot be converted into areliable estimate of the vapor pressure throughout the system. Without careful control and measurement of temperatures in the regions occupied by sample and by sensor, no meaningful data can be collected. 

Introduction of room-temperature ionic liquids (RTIL) as electrochemical media promises to enhance the utility of fuel-cell-type sensors (Buzzeo et al., 2004). These highly versatile solvents have nearly ideal properties for the realization of fuelcell-type amperometric sensors. Their electrochemical window extends up to 5 V and they have near-zero vapor pressure. There are typically two cations used in RTIL V-dialkyl immidazolium and A-alkyl pyridinium cations. Their properties are controlled mostly by the anion (Table 7.4). The lower diffusion coefficient and lower solubility for some species is offset by the possibility of operation at higher temperatures. 

This study represents the first systemmatic application of the optical waveguide technique to the study of the response of polymer film coatings to condensed vapor molecules. These results indicate that the technique is useful for surveying rapidly potential polymeric films as possible vapor sensor coatings. Moreover, this work has further substantiated that the vapor pressure is an important physical property to be taken into account when employing polymeric films as surface coatings. 

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