Torque Method

Fig. 6.6.6. TORQUE method [16] adapted for the measurement of H—> CP rates free of...

In order to reduce further the uncertainties due to spin-orbit interactions between nearly degenerate states close to the Fermi level Wang el al. [162] proposed a torque method. They illustrated the method by considering a uniaxial system where the energy can be well approximated by... 

In another series of experiments, Argyle et al. (1967) have compared the magnetoelastic component of the expansitivity, measured on a single crystal of EuO from 25 to 250 K, with the magnetic heat capacity above and below the Curie temperature, and find them accurately proportional to each other. They point out that this result is compatible with models proposed by Mattis and Schultz (1963), Pytte (1965), and Callen and Callen (1965). The temperature variation of the anisotropy constant Xi, determined by a static torque method by Miyata and Argyle (1967), is found to be in... 

In the case of Tb, the most systematic data for kI T) are those of Feron et al. deduced from measurements of the c-axis magnetization leading to k2(0) = 9.0 1.8 X 10 Jm From the zero-torque method, Rhyne and Clark estimated K2(0) = 8.7 2.2 X idi Jm . In their analysis of the spin wave energy gap in Tb (section 2.1.1) Roeland et al. (1975) derived a value (0.23 meV/ion) for the microscopic parameter Using eq. 6.42, this result is equivalent to k (0) = 7.6xlO Jm, in agreement with the macroscopic values within experimental error. 

The neck orbit was not detected, however, in the above mentioned dHvA measurements done by Ishizawa et al. (1977) and Arko et al. (1976). Later, branches p,- (/= 1,. .., 6) shown in fig. 8 by open circles were detected by the torque method (Ishizawa et al. 1980) and were attributed to the necks because the angular dependence of branches p, are consistent with the topologies of the necks. This Fermi surface of the neck is, however, thin and rather cylindrical, which is inconsistent with the short and thick neck constructed from the unobserved region of the ellipsoidal branches a, and also the results of band calculations. This puzzle was solved later by a combination of the improved ultrasonic dHvA measurements done by Suzuki et al. (1988) and the carefiil band calculations done ty Harima et al. (1988). In fig. 9c twelve pocket Fermi surfaces calculated by Harima et al. are shown as an enlarged scale by a factor of ten. It was shown that branches p, are not due to the necks but due to the small and flat electron Fermi surfaces. The data shown as triangles in fig. 8 were obtained by the ultrasonic dHvA measurements (Suzuki et al. 1988), The complete observation of branches p3 and ps is a clear evidence for existence of the small closed Fermi surfaces. 

Variation in bolt preload is dependent on degree of automation of torquing method and frictional conditions at the component interfaces. Both should be controlled wherever possible. 

Fig. 7 shows the torque necessary to obtain the specified body force under construction conditions and in tbe state when removed from the bridge. It can well be seen that the change of the friction coefficient causes a very big scattering, and the necessary torque is much bigger than specified. The distribution of the results of a measurement performed on 1,127 bolts is presented in Figure 8. An average of 80% of nominal body force was found by the new method. The traditional method found the nuts could be swivelled much further than specified on 42 bolts, these bolts were found to have 40 - 60 % body force by the new method. 

The traditional method for investigating the forces originating in the body of the bolt, which is based on measuring the torque of the nut, can detect only the bolts with a very great lack of body force since tbe friction coefficient worsens with time. 

Power. There are two main ways to measure the power deUvered by the driver to the pump. The first method is to install a torque meter between the pump and the driver. A torque meter is a rotating bat having a strain gauge to measure shear deformation of a torqued shaft. Discussion of the principle of torque meter operation is available (16). The benefit of this method is direct and accurate measurements. The power deUveted to the pump from the driver is calculated from torque, T, and speed (tpm) in units of brake horsepower, ie, BHP (eq. 4a) when Tis in lbs-ft, and kW (eq. 4b) when T is N-m. 

The disadvantages of this method ate the need for a torque meter, longer total length of the pumping unit, and greater susceptibiUty to misalignment and vibrations. This method is used only at a manufacturer s test faciUties or research laboratories. It is not used in the field. 

Various coupling designs are available to transmit torque from the driver, eg, electric motor, to a pump. In order to contain the pumped fluid inside the pump and prevent the pumpage from leaking, several types of sealing methods are used. A few options are described herein. 

The equations and methods for determining viscosity vary greatly with the type of instmment, but in many cases calculations may be greatly simplified by calibration of the viscometer with a standard fluid, the viscosity of which is known for the conditions involved. General procedures for calibration measurement are given in ASTM D2196. The constant thus obtained is used with stress and shear rate terms to determine viscosity by equation 25, where the stress term may be torque, load, or deflection, and the shear rate may be in rpm, revolutions per second (rps), or s F... 

Butterfly Valves These valves (Fig. 10-155) occupy less space in the line than any other valves. Relatively tight sealing without excessive operating torque and seat wear is accomphshed by a variety of methods, such as resilient seats, piston rings on the disk, and inclining the stem to limit contact between the portions of disk closest to the stem and the body seat to a few degrees of curvature. 

Control of wound-rotor motors, as discussed, can be effected by adjusting the external secondaiy (rotor) resistance either in steps or continuously by liquid rheostat (this method is seldom used). Commonly when secondaiy resistance is varied to adjust speed or torque or to control acceleration, multiple resistance steps are used. These steps may be switched manually (typically a drum switch) or electrically by contac tor. 

This expression, except for the mechanical design, is totally independent of the type of start and the electrical design of the motor. Electrically also, this is demonstrated in I he subsequent example. The expression, however, does not hold good for an ON-LOAD start. On load, the accelerating torque diminishes substantially with the type of load and the method of start, as can be seen from Figure 2.14, and so diminishes the denominator of equation (2.5), raising the time of start. 

The simplest method is performing it manually. Once the total external resistance is known, the resistance unit can be built with a hand-operated mechanism to manually cut-off the external resistance. However, this method is suitable only for applications where the magnitude of torque during the pick-up period (torque at different... 

Such a control is good for machines that are required to operate at low speeds with a high accuracy. Now the phasor /, in terms of /, , is varied according to the speed required. Figure 6.2 now changes to Figure 6.8, which is a marked improvement on the earlier characteristics. The torque variation with speed is now almost constant, except at very low speeds. The reason for poor torque at low speeds is the method of speed variation which is. still based on Vlf. Now a motor s mathematical model is used... 

The rotor flux-oriented control is more popular among different manufacturers to achieve high precision of speed control in an induction machine. With this technology (any of the three methods noted above), it is now possible to obtain a high performance of the machine, i.e. torque up to 100% of Tr at speeds down to zero. 

The inverter may be a current source inverter, rather than a voltage source inverter (.Section 6.9.4) since it will be the rotor current that is required to be vtiried (equation (1.7)) to control the speed of a wound rotor motor, and this can be independently varied through the control of the rotor current. The speed and torque of the motor can be smoothly and steplessly controlled by this method, without any power loss. Figures 6.47 and 6.48 illustrate a typical slip recovery system and its control scheme, respectively. 

There are several methods of braking, external or internal, and they are briefly diseussed below. Any of them can be employed, depending upon the torque requirement, i.e. size of motor, its speed, the type of load, etc. 

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