Signal mass-flow sensors

R 18] [A 1] Each module is equipped with a heater (H3-H8) and a fluidic cooling (C03-C06). Temperature sensors integrated in the modules deliver the sensor signals for the heater control. Fluidic data such as flow and pressure are measured integrally outside the micro structured devices by laboratory-made flow sensors manufactured by silicon machining. The micro structured pressure sensor can tolerate up to 10 bar at 200 °C with a small dead volume of only 0.5 pi. The micro structured mass flow sensor relies on the Coriolis principle and is positioned behind the pumps in Figure 4.59 (FIC). For more detailed information about the product quality it was recommended to use optical flow cells inline with the chemical process combined with an NIR analytic or a Raman spectrometer. 

Altitude Response. Pressure response is an issue that needs to be addressed for every instrument deployed on an aircraft. First, it must be decided how chemical abundances are to be reported. If standard practice is followed and they are reported as mixing ratios, then it must be determined whether the instrument is fundamentally a mass- or a concentration-depen-dent sensor, because this definition determines the first-order means by which instrument response is converted to mixing ratios as a function of pressure. In this context, a mass-sensitive detector is a device with an output signal that is a function of the mass flow of analyte molecules a concentration-sensitive detector is one in which the response is proportional to the absolute concentration, that is, molecules per cubic centimeter. 

Some altitude effects on the operation of chromatographic instruments are anticipated. To achieve reproducible retention times for identifying compounds, mobile-phase flows need to be controlled so that they are independent of ambient pressure. Detectors may also respond to changes in pressure. For example, the electron capture detector is a concentration-sensitive sensor and exhibits diminished signal as the pressure decreases. Other detectors, such as the flame ionization detector, respond to the mass of the sample and are insensitive to altitude as long as the mass flow is controlled. 

In addition, the analyzer can accept analog signals From other field-mounted analyzers or sensors such as flowmeters and pressure transducers. The signal can be sealed, digitized, and incorporated into special calculations to determine mass flow, therms per day, reactor yields, and so on. 

Moreover, a CRT-equipped heavy-duty diesel engine was investigated utilizing the partial flow sensor head applied to the secondary dilution tunnel of a full flow CVS system. (Anderson, 2003). In Figure 35 the EC mass concentration during a ETC test cycle is depicted for four consecutive tests. From these measurements, it could be seen that LII is feasible to detect EC mass concentrations with high signal dynamics and... 

The methodology was applied to fed-batch baker s yeast production on a 200-m3 scale [33]. The typical phases in a baker s yeast cultivation were visualized including lag phase, formation and consumption of ethanol and increase and decrease of cell mass. Fusion of signals from external sensors for volume, aeration flow rate and dissolved ethanol resulted in different character of the trajectory in the PCA but with the same principal information. 

If an extensive signal is to be measured with a low-cost microdevice that can be batch-manufactured, the signal has to first be converted into an intensive signal. For example, the mass flow (extensive) in a tube may be represented by the mass-flow density (intensive) at a small region within the tube. To ensure correct correlation between mass-flow density and mass flow, however, the tube itself becomes an essential part of the measuring setup. Consequently, such sensors are often not testable before their manufacturing process is entirely complete. The stage of production at which a sensor can be tested is cmcial, because it can be ten times cheaper to discard a sensor chip than to discard the complete sensor. 

Obviously, a sensoTs function can be tested at the end of the fabrication process after the sensor is completely assembled and fully packaged. At this time a primary input signal (pressure, acceleration, yaw rate, mass flow, etc.) can be applied directly, and a comprehensive test of the specified performance is possible. Unfortunately, by the time a defective sensor component is packaged, loss of time and capital is maximum, since a fully packaged sensor needs to be discarded. 

When a built-in self test is not feasible, we encounter difficulties because primary input signals cannot be easily provided within a standardized probe setup. To our knowledge, no commercial testing equipment is available that allows a set of primary stimuli like acceleration, pressure, torque, or mass flow to be applied to the transducer elements of sensor chips on the wafer level, with the required speed and precision. At the moment we are therefore left with purely electrical stimuli for testing microsensor devices. 

Energy balance thermal mass meters require one heating element located between two temperature sensors as illustrated in Figure 4.21 [24]. Although several design variations exist, their operation is basically similar. As the fluid flows past the heating element, it absorbs heat. This heat is carried downstream where it is transferred to the downstream temperature sensor. The temperature difference between the upstream and downstream sensor is detected. This output signal is then converted into a mass flow rate. These meters typically have a turn down ratio of 10 1 while the constant temperature and constant power meters have a turndown ratio of 1000 1 and 100 1, respectively. 

In the case of the latter alternative, the set volumetric flow rate is attained via Mass Flow Controllers (MFC). Using this method, complete chains of analyzers can be automatically calibrated with ease. The MFCs receive a signal between 0 and 5 V and transform this into the corresponding flow rate. A sensor then measures the flow rate and a controller aligns the actual value with the set point via a metering valve, thereby controlling the dosing process. 

The local temperature field depends on the quality and velocity of fluid medium, integrates on a chip of the sensor to measure temperature distribution through calibration. The specially designed signal processing circuit will be converted to mass velocity and mass flow rate of medium into a linear relationship between output voltage value (Durst F 2003). 

CUl and CU4 are value-keeping controllers for the control of the outlet temperatures of the collector and of the HWS heat exchanger, respectively. Control signals are produced by the temperature sensors Tqc and Tw- Control is realized by changing the mass flow rates with one-way motor valves Vq and respectively. 

Typically, increasing the volumetric flow rate through the sensor increases the mass transport of the analyte to the working electrode, thereby increasing the observed signal (i.e.,... 

Any experiment suffers to some extent from the influence of various uncontrolled factors, such as mass- and heat-transfer regimes in different parts of the reaction system, irregularity of temperature fields and flow profiles, dead spaces, poor mixing, and independent flow of reactants, wall chemistry and its variation with time, etc. Another problem is a correlation between signals received from different sensors and real values of measured physical parameters. There is a voluminous literature on this subject here we just mention the pitfalls related to the measurements of surface and gas temperatures in the course of reaction involving very active radical species. 

Fig. 7.6.2 Electrical layout of the Bosch microsilicon sensor element for air flow. The different resistors are shown in different colors. The air mass signal is generated using the resistors Rabl, Raul, Rab2, Rau2 in a Wheatstone bridge...

---