. Graphical and mechanical computation . may coincide or make any convenient angle with AX. On these axesconstruct the scales x = ntifi(u), y = ra2/2(z>), z = m3fs(w), t = mif4(q) where the moduli are arbitrary except for the relation nti : m2 = m3 : read the chart, use twoindex lines, one joining uand v, and the other join-ing w and q, and intersect-ing in a point on AB. The following examplesillustrate this type of chart: 35. Prony brake orelectric dynamometer ( . „„ 2TTLNW formula, = . 33,000 for measuring the power of a rotating shaft. Either the prony brake or the electric d
. Graphical and mechanical computation . may coincide or make any convenient angle with AX. On these axesconstruct the scales x = ntifi(u), y = ra2/2(z>), z = m3fs(w), t = mif4(q) where the moduli are arbitrary except for the relation nti : m2 = m3 : read the chart, use twoindex lines, one joining uand v, and the other join-ing w and q, and intersect-ing in a point on AB. The following examplesillustrate this type of chart: 35. Prony brake orelectric dynamometer ( . „„ 2TTLNW formula, = . 33,000 for measuring the power of a rotating shaft. Either the prony brake or the electric dynamometer may be used. With such an arrangement the power is given by the above formula, where L is the length of brake arm in feet, N is the speed of the shaft in revolutions per minute, and W is the load on scale in pounds. If we write the equation as W A7 ? = —??—tt , we have an equa-N 5260/L M tion of the form (IV), and our scales are x = , y = m2N, 5260 Fig. sketch in Fig. 35a gives the method. z = m3W, t = m\ L 0 BO Fig. 356. The following table exhibits the limits of the variables, the choice of moduli, and the equations and approximate lengths of the scales. NW Limits Modulus o to 80 Wi = to 5000 mi = to 400 ms = W2OT3 to 5 w4 = Wl Equation Length x = 12 y = -N ill z = W 12 t - 2-37 a L In Fig. 35&, the x- and z-axes coincide, so that the and W-scalesare laid off on opposite sides of the common axis, and starting from thp ?0 NOMOGRAPHIC OR ALIGNMENT CHARTS Chap. IV same origin; similarly for the N- and L-scales. The index lines, onejoining L and W and the other joining N and intersect on the trans-versal joining the zero points of the scales. The completed chart is given in Fig. 35c, and the index lines show thatwhen L = 2 ft., W = 50 pounds, and N = 2000 , then = 38. O Co *1 SI
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