Quadrantes

Fig. 8 Scan showing single quadrant wastage. Fig. 9 Circumference and localised wastage. Highly located...

Historically, the first and most important capacitance method is the vibrating capacitor approach implemented by Lord Kelvin in 1897. In this technique (now called the Kelvin probe), the reference plate moves relative to the sample surface at some constant frequency and tlie capacitance changes as tlie interelectrode separation changes. An AC current thus flows in the external circuit. Upon reduction of the electric field to zero, the AC current is also reduced to zero. Originally, Kelvin detected the zero point manually using his quadrant electrometer. Nowadays, there are many elegant and sensitive versions of this technique. A piezoceramic foil can be used to vibrate the reference plate. To minimize noise and maximize sensitivity, a phase-locked... 

Another way to identify correlations is to plot the values of the parameters in graphical form this can help to identify any correlations and the presence of outliers. A Craig plot is a two-dimerrsional scatterplot of one parameter against another ideally, the molecules should sample from all four quadrants of the plot. 

The vector in Fig. 2-2 happens to fall in the fourth quadrant as drawn. The number pair giving the point that coincides with the tip of the arrow gives its magnitude and direction relative to the coordinate system chosen. Magnitude and direction are all that you can know about a vector hence it is completely defined by the number pair (5,-1). 

A two-sample chart is divided into four quadrants, identified as (-P, -p), (-, -p), (-, -), and (-P, -), depending on whether the points in the quadrant have values for the two samples that are larger or smaller than the mean values for samples X and Y. Thus, the quadrant (-P, -) contains all points for which the result for sample X is larger than the mean for sample X, and for which the result for sample Y is less than the mean for sample Y. If the variation in results is dominated by random errors. 

Fig. 6. Orifice plates (a) concentric, (b) eccentric, (c) segmental, (d) universal, and (e) quadrant-edge.

For perm anen t-m agnet materials where the coercivity is large, the demagaetizatioa curve, which correspoads to the secoad quadrant of the hysteresis loop, sometimes is plotted as the polarization J(= B — vs H(B — H vs H) to show the intrinsic characteristics of the material. The value of... 

H, for which J = 0, is the intrinsic coercivity whereas the usual coercivity, for which S = 0, is denoted by H or H. For permanent magnets, the value (BH), the maximum energy product, is an important measure of quaHty. The value (BH), iadicated ia the secoad quadrant of Figure 1, represents the poiat of maximum efficieacy where a givea amouat of magnetic flux is produced by the smallest amouat of material. 

The trigonometric functions of angles are the ratios between the various sides of the reference triangles shown in Fig. 3-39 for the various quadrants. Clearly r = /x + y > 0. The fundamental functions (see Figs. 3-40, 3-41, 3-42) are... 

Permanent pressure loss across quadrant-edge orifices for turbulent flow is somewhat lower than given by Eq. (10-30). See Alvi, Sridharan, and Lakshmana Rao, loc. cit., for values of discharge coefficient and permanent pressure loss in laminar flow. 

FIG. 21-24 a) Rack-and-pinion gate, (h) Double-quadrant gate. 

Note A hah -wcive rectifier is a single-bridge rectifier ami is suitttble tor only sirigle-qtittdrarit operations 1 or lit.. A fuM-wine rectifier is a dotible-bridge rectifier ttnd suitable for multi-quadrant operations particularly quadrants 11 and IV.. See Table 6.4. 

A cttnirolled rectifier unit is necessary when it has to control a d.c. machine, which w ould call for i variable d.c, voltage. When the d.e. machine has to operate in only one direction (quadrants I or III) a half-wave controlled rectifier w ill be adequate and when the machine has to operate in either direction, a full-wave controlled rectifier will be essential. 

For operations in quadrants II and IV it is essential to have m unrestricted How of reverse power and hence an... 

Depending upon the mode of operation of a motor, the type of converter unit can be decided. For. simplicity, the operation (conduction) of a motor can be represented by four quadrants as illustrated in Table 6.4. 

Quadrant I Both V and / are positive. The machine can be run only in one direction (say. forward). Braking operations are possible. It is a converter mode and cither a half-wave or a full-wave rectifier can be used. 

Quadrant II Now / is in the reverse direction and the machine can be run in the reverse direction. Braking and regeneration are possible. For regeneration an additional bridge will be essential as discussed later. For current to flow in either direction, a full-wave rectifier w ill also be essential. 

Quadrant III Now both the voltage and the torque arc in the reverse direction otherwise it is similar to Quadrant I. The machine can now be run in the reverse direction. 

Table 6.4 Operation of a motor in different modes and the corresponding conducting quadrants of a controlled converter unit...

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