Gas Test Measurements

The noise in the sensor signal is 0.5 digits. This corresponds to a 1-digit quantization noise of the A/D converter. At low concentration levels, the noise is equivalent to a CO-concentration variation of 0.03 ppm. Multiplying this value by three, the Emit of detection was assessed to be 0.1 ppm. The gas concentration resolution amounts 

The proportional constant, c, includes the conversion relation of the A/D converter and the factor kTclq of Eq. (5.3). Since the measurement chamber is temperature-stabilized, the chip temperature, Tc, is constant. is the resistance of the sensitive layer in synthetic air, and R is the resistance upon analyte exposure. Equation (5.7) relates AS to the ratio fig /R, which is commonly plotted as sensor signal for reducing gases. 

The sensor response at a defined relative humidity of 40% (23 °C humidifier temperature) is displayed in Fig. 5.13 for various microhotplate temperatures. AS in- 

In order to assess the dependence of the output signal on changes in the humidity content of the sample gas, an additional series of measurements was carried out. The hotplate temperature was set to 275 °C, and CO measurements were recorded at three different humidity levels (10, 20 and 40% r.h.) The humidifier temperature was set to 23 °C, and the chip temperature was 30 °C. As can be seen in Fig. 5.14, the sensor response increases with increasing humidity. The large sensor response difference between 10% and 20% r.h. shows that this effect is more pronounced at low humid- 

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. 

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The microhotplate was coated with a thick-film tin-oxide droplet as described in Sect. 4.1.2. To characterize the chemical-sensor performance, the chip was exposed to CO concentrations from 5 to 50 ppm in humidified air at 40% relative humidity (23.4 °C water vaporization temperature) (see Sect. 5.1.8 for a description of the gas test measurement setup). 

A control experiment was performed with an uncoated microhotplate in the gas test measurement setup with the same measurement program and at the identical microhotplate temperature. No changes in the source-gate voltage could be measured. Therefore, the changes in the microhotplate heat budget are clearly related to the interaction of the analyte with the tin oxide. 

The negative sign is a consequence of the polarity of the differential output voltage Lowering the sensor resistance leads to an increased V s- Equation (5.3) will be used for further discussions of the sensor signal in the section on gas test measurements (Sect. 5.1.9). 

Gas test measurements were performed with this device, and a novel sensor operation mode was developed and successfully demonstrated (Sect. 4.5) calorimetric-type signals could be recorded as changes in the source-gate voltage of the transistor while maintaining a constant microhotplate temperature. 

The Reich test is used to estimate sulfur dioxide content of a gas by measuring the volume of gas required to decolorize a standard iodine solution (274). Equipment has been developed commercially for continuous monitoring of stack gas by measuring the near-ultraviolet absorption bands of sulfur dioxide (275—277). The deterrnination of sulfur dioxide in food is conducted by distilling the sulfur dioxide from the acidulated sample into a solution of hydrogen peroxide, foUowed by acidimetric titration of the sulfuric acid thus produced (278). Analytical methods for sulfur dioxide have been reviewed (279). 

Table 6.2 presents an overview of surface-emissive powers measured in the British Gas tests, as back-calculated from radiometer readings. Peak values of surface-emissive powers were approximately 100 kW/m higher than these average values, but only for a short duration. Other large-scale tests include those conducted to investigate the performance of fire-protection systems for LPG tanks. 

For comparing the relative loss of a flavor component from a container, we have found the sniff test (6) very useful, especially when gas concentration measuring techniques were not available. Typical results of this type of test are shown in Table II. Each filled container was held in a glass jar for approximately 48 hours. The results are stated in qualitative, subjective terms such as slight, strong, or undetectable. The... 

The second method to calculate of void fraction is based on gas velocity measurement. A high-speed motion analyzer was employed by Zhao and Bi (2001b) to visualize bubble behavior in the test sections. 

Various aspects of in vitro gas production test have been reviewed by Getachew et al. [33], and these authors reported that gas measurement were centered on investigations of rumen microbial activities using manometric measurements and concluded that these methods do not have wide acceptability in routine feed evaluation since there was no provision for the mechanical stirring of the sample during incubation. Another in vitro automated pressure transducer method for gas production measurement was developed by Wilkins [34], and the method was validated by Blummel and Orskov [35] and Makkar et al. [36]. There are several other gas-measuring techniques such as (i) Flohenheim gas method or Menke s method [37] (ii) liquid displacement system [38] (iii) manometric method [39] (iv) pressure transducer systems manual [40], computerized [41], and combination of pressure transducer and gas release system [42]. 

The method was tested with two wood fuels, namely wood pellets and fuel wood. The mass flow of conversion gas was measured at three levels of standard volume flows of primary air (50,100, and 150 m n/h). Double tests were carried out at each volume flow of air. The mass-balance result is presented in Table 1 and Table 2 above. 

Direct sampling and analysis of the effluent stream may be used to determine the solubility of the heavy phase in the volatile component (often a supercritical fluid). Alternatively, the composition can be determined from the total volume of gas (i.e., of the supercritical fluid after expansion) passed through the saturator, and from the known mass of solute extracted during die sample-collecting period. The efflluent stream is expanded to atmospheric pressure via an expansion valve. Then it passes through a cold trap, where the extract is quantitatively precipitated or condensed, and finally proceeds to a dry-test or a wet-test gas meter or other device, where the total amount of the passed gas is measured. The amount of extracted solute... 

A certain mass flowmeter (see Section 6.2.3) was tested (calibrated) by comparing the readings given by the instrument G with true (known) values GT of the flow of a gas as measured by the instrument in a 0.15 m ID pipeline. True and measured values are compared in Fig. 6.61 and Table 6.17. Estimate the errors in the flowmeter due to bias and imprecision. Assume that variations in the input and output of the instrument are normally distributed. 

As pressure is increased above the bubble point pressure, pores of decreasing size have the liquid forced out, and this allows additional bulk flow of the test gas. By measuring and comparing the bulk gas flow rates of both a wetted and a dry filter medium at the same pressure, the percentage of the bulk gas... 

In practice, pyro-gas will always contain some non-condensed light oils. Table 8-5 gives the composition of the light oil condensed from pyro-gas at 0 C (32 F).4 Listed among the components are toluene, benzene, hexane, styrene, and xylene. Emissions of benzene, ethylbenzene, toluene, and xylene were measured in the stack test at Conrad Industries. Flow rates for the tests measuring these compounds were not reported thus, emission rates (lbs/MMBtu) could not be estimated. 

It should be kept in mind that any change in surface area, surface chemistry, or microporosity will result in a change in the energy of immersion. Because immersion calorimetry is quantitative and sensitive, and because the technique is not too difficult to apply in its simplest form, it can be used for quality testing. The preliminary outgassing requires the same care as for a BET measurement, but, from an operational standpoint, energy of immersion measurements are probably less demanding than gas adsorption measurements. 

Investigators of tower packings normally report k Ga values measured at very low inlet-gas concentrations, so that yBu = 1, and at total pressures close to 100 kPa (1 atm). Thus, the correct rate coefficient for use in packed-tower designs involving the use of the driving force (y - yt)/yBM >s obtained by multiplying the reported k Ga values by the value ofpT employed in the actual test unit (e.g., 100 kPa) and not the total pressure of the system to be designed. 

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