Resistive grid

I Normally the external resistances are connected in star. But for larger motors, calling for high resistance grids, they may also be connected in delta, to reduce their current rating and hence the cost. Insulation is not a limiting factor usually, in case of resistance grids. 

More importantly, such alloys also possess a very low temperature coefficient of electrical resistance (of the order of 220 idQ.IQ.rC, typical), which causes only a marginal change in its resistance value with variation in temperature. They can therefore ensure a near-consistent predefined performance of the motor for which the resistance grid is designed, even after frequent starts and stops. They are also capable of absorbing shocks and vibrations during stringent service conditions and are therefore suitable for heavy-duty drives, such as steel mill applications. 

In this case the regulating resistance grids arc normally continuous duty, unlike those for stail-up, which arc short-time duty. Equations (5.1 a-d) can be used, for determining the total rotor circuit resistance for a particular speed variation, i.e. 

Figure 7.17 Moore s hardware implementation of Land s algorithm (Reproduced by permission of IEEE. Moore A and Allman J and Goodman RM 1991 A real-time neural system for color constancy. IEEE Transactions on Neural Networks, IEEE, 2(2), 237-247, March). The output of the camera is smoothed using three separate resistive grids (a). A single resistive grid is shown in (b). The smoothed image is then subtracted from the original image.

Moore et al. (1991) have also developed an extension to Land s retinex algorithm in order to reduce the effect of color induction. The modified algorithm computes the magnitude of the first spatial derivative. This derivative is also smoothed with a resistive grid. A blurred version of the input image is computed as before. The smoothed version of the derivative is used to modulate the blurred version of the input image before it is... 

Let us now take a look at the function computed by the resistive grid. 

Let us consider the one-dimensional case again. Figure 10.14 shows a linear network of resistors. If we carry out the same derivation as mentioned earlier but now for a onedimensional resistive grid, we arrive at the following equation (Jahne 2002) ... 

In order to compute the output of the two-dimensional resistive grid using a convolution, we have to find the inverse Fourier transform of... 

Figure 10.15 Results for the resistive grid are shown in (a) and (b). Results for an expo-...

Figure 10.18 A comparison between the computed and the actual illuminant along a horizontal line of the image (marked by a white line in Figure 10.17). Local space average color is computed using an exponential kernel, a Gaussian kernel, or a resistive grid.

---