Dynamic Calibration

The shear stress sensor for turbulent flow needs to accurately capture the complete turbulent fluctuation spectrum. Therefore, the shear stress sensor should possess a large bandwidth with flat and minimum frequency-phase relationship. For direct measurement by floating point sensors, the resonant frequency of the floating element and the fluidic damping determines the usable bandwidth. For the thermal sensor, the thermal inertia of the sensor element and the 

The solution of compressible momentum equation provides the relationship between the shear stress, pressure gradient, and excitation frequency as 

V(f) is the sensor voltage, t(/) is the shear stress calculated from equation (12.27) as a function of the pressure flucmation magnitude, and is the static sensitivity from the static 

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Evaluation and calibration. A piece of tube was rotated around its own axis during four channel wall thickness mea.surements (Figure 7). The four traces are not identical A rotation apart as should be expected. The calibrations of the four equipment s from the manufacture was not the same. Especially one of the traces has less dynamic than the other three. Based on these observations a dynamic calibration system was suggested using a tube, which could be rotated around its own axis in the measuring system. The values should be verified using traditional mechanical measurement around the tube circumference. The prototype system was permanently installed in the workshop at the production hall. Experimental work was more difficult under such circumstances so our participation in the development work stopped. 

Dharmarajan V, Rando RJ. 1980. Dynamic calibration of a continuous organo-isocyanate monitor for hexamethylene diisocyanate. Am Ind Hyg Assoc J 41(6) 437-441. 

The above standard mixtures contained in cylinders are supplemented by several gas measurement facilities which can provide dynamic calibrations of gas mixtures and of gas monitoring instruments. These include an on-line facility which injects gas dynamically into a passivated multipass optical gas cell, where the gas concentration is certified spectroscopically. Some of the gas mixtures which can be certified by these dynamic blending facilities are given in Table 2. 

If the soil suspension were instead an aqueous solution, a scale of activity values for Na+ could be defined in terms of emf data obtained for standard reference solutions of prescribed (Na+), in exactly the same way as the scale of (H) values (the operational pH scale) is defined (arbitrarily) in terms of emf data for standard buffer solutions.39,40 However, the success of this extrathermo-dynamic calibration technique depends entirely on the extent to which E, and B in the standard reference solutions are the same as E, and B in the solution of interest. For the case of a soil suspension, the presence of colloidal material may cause these two parameters to differ very much from what they would be in a reference aqueous solution. If the difference is indeed large, the value of (Na+), m, or any other ionic activity estimated with the help of standard solutions and an equation like Eq. s2.23 would be of no chemical significance. 

In most cases, the measuring devices are not described in detail, and little information is given on the calibration techniques which were used. Most workers have recognized that the effects of friction, of static vs. dynamic calibrations, etc., can be very important, and have attempted to minimize errors from these sources. Further quantitative work on the properties of these dynamometer systems would be useful. Nevertheless, from the point of view of providing data suitable for engineering application, these different types of power measurements give results which are reasonably consistent. 

Fig. 4. Load/time trace from a typical test. Viscoelastic delay of strain recovery in the PMMA Hopkinson bar is compensated for by dynamic calibration.

The determination of the constants S and t constitutes the static and dynamic calibration of the calorimeter. The calibration of the calorimeter may be done by means of a known thermal effect produced during suitable conditions inside the cell, for example. Joule effect calibration (2, 4, 41). 

A dynamic calibration check was obtained at sea for both fluorome-ters from a chlorophyll transect obtained by towing a Batfish and submers-... 

From pure gases, dynamic calibration gas generators can produce a deHned gas mixture with a defined flow rate (see Figure 16-2). With the exception of those calibration gas generators that operate on the basis of permeable membranes, pure gases or binary gas mixtures are dosed and mixed in the desired proportion. The number of required gas cylinders is reduced to the number of required components [3]. 

The Stokes-layer excitation in a cylindrical duct is one of the effective techniques for dynamic calibration of shear stress sensors [8]. The flow inside the duct is driven by an oscillating pressure gradient generated by a loud speaker (see Fig. 10). The loud speaker driven by an amplifier generates an acoustic wave. The amplifier receives sinusoidal input from a function generator. The microphone and shear stress sensor are mounted at opposite locations of the tube. The data acquisition system records the signal from the microphone and shear stress sensor. 

Shear Stress Sensors, Fig. 10 The schematic of a dynamic calibration apparatus for the shear stress sensor... 

Sheplak M, Padmanabhan A, Schmidt MA, Brener KS (2001) Dynamic calibration of a shear-stress stat-sor using Stokes-layer excitation. AIAA... 

Commonly, the heat capacity signal is calibrated at a single temperature. However, the experimental error on the heat capacity can further be reduced by a dynamic calibration over the entire temperature range instead of at a single temperature. The heat capacity calibration constant, Kc., shows a gradual evolution over the entire temperature range, with a total variation of 4% between —50 and 300°C. Below —50°C, the deviation increases. 

If the pressure sensor of the CTD responds to fast changes in temperature, it is corrected for according to the results of its dynamic calibration (Section 3.6.3). The correction starts with the pre-cast deck values thus assuming that the sensor is close to thermal equilibrium. 

Figure 40.3 presents an example of the drive signal used for dynamic calibration, while Fig. 40.4 illustrates an expanded version of a portion of this time series (i.e., contained between 180 and 210s). 

Fig. 40.3. Wave machine drive signal for dynamic calibration.

Fig. 40.5. Complex transfer function obtained by dynamic calibration.

F Davide, C Di Natale, A D Amico, A Hierlemann, J Mitrovics, M Schweizer, U Weimar, and W Gopel, "A Novel Neural Network System for the Recognition of Gas Mixtures", Conf Proc 5th Int Meeting on Chemical Sensors. Rome (I) 7/1994, and Sensors and Actuators, in press F Davide, C Di Natale, A D Amico, A Hierlemann, J Mitrovics, M Schweizer U Weimar, and W Gopel, "Autoregressive Techniques for Dynamical Calibration of Sensor Arrays Based on QMB Polymer Coated Sensors" Conf Proc 5th Int Meeting on Chemical Sensors, Rome (I) 7/1994, and Sensors and Actuators m press... 

Vz will be negative since the vertical force is decreased, and Vh will be positive since the force is in the east direction. This method is very simple and can determine the generator constant accurately, but will not give a dynamic calibration. The horizontal components can be tested for symmetry by inclining in the opposite direction. In the case that the instrument output is not zero in the horizontal position, this offset should be adjusted before any measurement is made alternatively it may be subtracted from the output for each measurement. 

Finally, we note that diffusion tubes can be used as an alternative to permeation tubes. These involve the use of a liquid reservoir which is connected to the external environment by a capillary. Vapour will diffuse along this tube at a fixed rate at a fixed temperature. Consequently, a diffusion tube can then be used in a similar manner to a permeation tube. However, diffusion tubes require more operator skill and are suitable for fewer compounds than permeation tubes. Permeation tubes are therefore used far more widely than diffusion tubes in dynamic calibration techniques. 

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