Fig. 100. Electromagnet with Terminals
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Where economy of space is necessary, a convenient method of terminating the winding of the coil consists in fastening rigid terminals to the spool head. This, in the case of a fiber spool head, may be done by driving heavy metal terminals into the fiber. The connections of the two wires leading from the winding are then made with these heavy rigid terminals by means of solder. A coil having such terminals is shown in its finished condition in Fig. 100.
Winding Data. The two things principally affecting the manufacture of electromagnets for telephone purposes are the number of turns in a winding and the resistance of the wound wire. The latter governs the amount of current which may flow through the coil with a given difference of potential at its end, while the former control the amount of magnetism produced in the core by the current flowing. While a coil is being wound, it is a simple matter to count the turns by any simple form of revolution counter. When the coil has been completed it is a simple matter to measure its resistance. But it is not so simple to determine in advance how many turns of a given size wire may be placed on a given spool, and still less simple to know what the resistance of the wire on that spool will be when the desired turns shall have been wound.
TABLE IV
Winding Data for Insulated Wires—Silk and Cotton Covering
| A.W.G. B & S | 20 | 21 | 22 | 23 | 24 | 25 | 26 |
| DIAMETER Mils | 31.961 | 28.462 | 25.347 | 22.571 | 20.100 | 17.900 | 15.940 |
| AREA Circular Mils | 1021.20 | 810.10 | 642.70 | 509.45 | 404.01 | 320.40 | 254.01 |
| DIAMETER OVER INSULATION | |||||||
| Single Cotton | 37.861 | 34.362 | 31.247 | 28.471 | 26.000 | 23.800 | 21.840 |
| Double Cotton | 42.161 | 38.662 | 35.547 | 32.771 | 30.300 | 28.100 | 26.140 |
| Single Silk | 34.261 | 30.762 | 27.647 | 24.871 | 22.401 | 20.200 | 18.240 |
| Double Silk | 36.161 | 32.662 | 29.547 | 26.771 | 24.300 | 22.100 | 20.140 |
| TURNS PER LINEAR INCH | |||||||
| Single Cotton | 25.7 | 28.3 | 31.0 | 34.4 | 36.9 | 38.0 | 42.0 |
| Double Cotton | 22.5 | 24.5 | 26.7 | 28.97 | 31.35 | 33.92 | 36.29 |
| Single Silk | 27.70 | 30.97 | 34.39 | 38.19 | 42.37 | 47.02 | 52.06 |
| Double Silk | 26.22 | 29.07 | 32.11 | 35.53 | 39.14 | 42.94 | 46.81 |
| TURNS PER SQUARE INCH | |||||||
| Single Cotton | 660.5 | 800.9 | 961.0 | 1183.0 | 1321.6 | 1444.0 | 1764.0 |
| Double Cotton | 506.3 | 600.2 | 712.9 | 839.2 | 982.8 | 1150.8 | 1317.0 |
| Single Silk | 767.3 | 959.1 | 1182.7 | 1458.5 | 1795.2 | 2210.9 | 2710.3 |
| Double Silk | 687.5 | 845.0 | 1031.0 | 1262.4 | 1532.0 | 1843.8 | 2191.2 |
| OHMS PER CUBIC INCH | |||||||
| Single Cotton | .646 | .981 | 1.502 | 2.359 | 3.528 | 5.831 | 6.941 |
| Double Cotton | .533 | .795 | 1.188 | 1.772 | 2.595 | 3.802 | 5.552 |
| Single Silk | .801 | 1.261 | 1.956 | 3.049 | 4.739 | 7.489 | 9.031 |
| A.W.G. B & S | 27 | 28 | 29 | 30 | 31 | 32 | 33 |
| DIAMETER Mils | 14.195 | 12.641 | 11.257 | 10.025 | 8.928 | 7.950 | 7.080 |
| AREA Circular Mils | 201.50 | 159.79 | 126.72 | 100.50 | 79.71 | 63.20 | 50.13 |
| DIAMETER OVER INSULATION | |||||||
| Single Cotton | 20.095 | 18.541 | 17.157 | 15.925 | 14.828 | 13.850 | 12.980 |
| Double Cotton | 24.395 | 22.841 | 21.457 | 20.225 | 19.128 | 18.150 | 17.280 |
| Single Silk | 16.495 | 14.941 | 13.557 | 12.325 | 11.228 | 10.250 | 9.380 |
| Double Silk | 18.395 | 16.841 | 15.457 | 14.225 | 13.128 | 12.150 | 11.280 |
| TURNS PER LINEAR INCH | |||||||
| Single Cotton | 48.0 | 53.0 | 56.5 | 59.66 | 64.125 | 68.600 | 73.050 |
| Double Cotton | 38.95 | 41.61 | 44.27 | 46.93 | 49.78 | 52.34 | 55.10 |
| Single Silk | 57.67 | 63.36 | 70.11 | 77.14 | 84.64 | 92.72 | 101.65 |
| Double Silk | 51.59 | 56.43 | 61.56 | 66.79 | 72.39 | 78.19 | 84.17 |
| TURNS PER SQUARE INCH | |||||||
| Single Cotton | 2304.0 | 2809.9 | 3192.3 | 3359.2 | 4112.2 | 4692.5 | 5333.5 |
| Double Cotton | 1517.2 | 1731.0 | 1959.9 | 2202.5 | 2478.0 | 2739.5 | 3036.1 |
| Single Silk | 3326.0 | 4014.5 | 4915.5 | 5950.2 | 7164.0 | 8597.5 | 10332.0 |
| Double Silk | 2661.6 | 3184.5 | 3789.8 | 4461.0 | 5240.0 | 6114.0 | 7085.0 |
| OHMS PER CUBIC INCH | |||||||
| Single Cotton | 10.814 | 17.617 | 25.500 | 34.800 | 48.5 | 73.8 | 104.5 |
| Double Cotton | 8.078 | 11.54 | 16.47 | 23.43 | 32.83 | 46.19 | 64.30 |
| Single Silk | 13.92 | 26.86 | 41.29 | 62.98 | 95.70 | 144.70 | 217.8 |
| A.W.G. B & S | 34 | 35 | 36 | 37 | 38 | 39 | 40 |
| DIAMETER Mils | 6.304 | 5.614 | 5.000 | 4.453 | 3.965 | 3.531 | 3.144 |
| AREA Circular Mils | 39.74 | 31.52 | 25.00 | 19.83 | 15.72 | 12.47 | 9.89 |
| DIAMETER OVER INSULATION | |||||||
| Single Cotton | 12.204 | 11.514 | 1090.0 | 10.353 | 9.865 | 9.431 | 9.044 |
| Double Cotton | 16.504 | 15.814 | 15.200 | 14.653 | 14.165 | 13.731 | 13.344 |
| Single Silk | 8.504 | 7.914 | 7.300 | 6.753 | 6.265 | 5.831 | 5.344 |
| Double Silk | 10.504 | 9.814 | 9.200 | 8.653 | 8.165 | 7.731 | 7.344 |
| TURNS PER LINEAR INCH | |||||||
| Single Cotton | 77.900 | 82.600 | 87.100 | 91.870 | 95.000 | 100.700 | 106.000 |
| Double Cotton | 57.57 | 60.04 | 62.51 | 64.70 | 66.80 | 68.80 | 71.20 |
| Single Silk | 112.11 | 119.7 | 130.15 | 140.6 | 151.05 | 163.04 | 177.65 |
| Double Silk | 90.44 | 96.90 | 103.55 | 110.20 | 116.85 | 122.55 | 129.20 |
| TURNS PER SQUARE INCH | |||||||
| Single Cotton | 6068.5 | 6773.3 | 7586.5 | 8440.0 | 9025.0 | 10140.5 | 11236.0 |
| Double Cotton | 3314.2 | 3605.0 | 3907.5 | 4186.1 | 4462.2 | 4733.6 | 5069.8 |
| Single Silk | 8179.5 | 9389.5 | 16940.0 | 19770.0 | 22820.0 | 26700.0 | 31559.0 |
| Double Silk | 8179.5 | 9389.5 | 10772.0 | 12145.0 | 13665.0 | 15018.0 | 16692.0 |
| OHMS PER CUBIC INCH | |||||||
| Single Cotton | 151.4 | 202.0 | 298.8 | 418.0 | 567.0 | 811.0 | 1113.0 |
| Double Cotton | 70.58 | 125.9 | 166.3 | 225.6 | 305.5 | 409.8 | 545.5 |
| Single Silk | 342.1 | 489.0 | 721.1 | 1062.0 | 1557.0 | 2266.0 | 3400.0 |